Keshav visits his friend Jatin’s village in the Western Ghats and is amazed by the forests, streams, and especially the glowing dance of fireflies at night.
He learns from Jatin’s grandparents that fireflies use light to communicate, but their numbers are falling due to light pollution and deforestation.
On the way back to the city, Keshav watches the moonlit hills and wonders — does the Moon produce its own light?
Or is it just reflected sunlight, like he read in his science book? As he thinks, he notices something interesting: light always travels in a straight line.
Sources of Light
Light enables us to see objects and is produced by various sources, both natural and artificial.
Natural Sources of Light
These include the Sun, stars, fire, lightning, and certain animals (like fireflies) that emit their own light.
Artificial Sources of Light
Humans have developed several artificial sources over time, beginning with fire created using fuels like oil and wax.
With technological advancement, electric lights such as bulbs, tube lights, and LED lamps have become common.
Luminous Objects
These are objects that emit their own light.
Examples include the Sun (the primary natural light source), stars, lightning, natural fire, and certain animals like fireflies.
Non-Luminous Objects
These objects do not produce their own light but reflect light from luminous sources. The Moon is a non-luminous object that shines by reflecting sunlight.
Other examples include planets like Mars and Venus, and everyday objects like mirrors.
Science and Society
LED lamps are energy-efficient, brighter, and longer-lasting than traditional bulbs. They help reduce electricity bills and are environmentally friendly. Recognizing these benefits, the Indian government actively promotes their use. However, used LED lamps must be properly recycled and not discarded in regular waste.
Try yourself:
What do fireflies use light for?
A.To communicate
B.To find food
C.To attract predators
D.To navigate
View Solution
Does Light Travel in a Straight Line?
Light travels in a straight line under normal conditions, a property known as rectilinear propagation.
When light passes through aligned holes in a straight line, it creates a bright spot on a screen.
If the holes are misaligned, no spot appears, indicating that light does not bend around obstacles.
Similarly, a candle flame is visible through a straight pipe but not a bent one, confirming that light follows a straight path.
Viewing candle flame through (a) a straight pipe (b) a bent pipe
Dive Deeper
Light generally travels in a straight line. This can be seen clearly when a laser beam passes through a medium like water. However, under special conditions, light can also bend — a fascinating concept you’ll explore in higher grades. Caution: Lasers should always be used under teacher supervision. Only low-power laser pointers are safe for basic use. Never point a laser at anyone’s eyes — it can cause serious injury.
Light Through Transparent, Translucent, and Opaque Materials
When light encounters different materials, its behavior depends on the material’s properties.
Transparent Materials
These allow light to pass through almost completely, enabling clear visibility of objects on the other side.
Examples include glass and clear plastic.
Translucent Materials
These allow light to pass through partially, causing diffused or blurred visibility.
Examples include tracing paper and frosted glass.
Opaque Materials
These block light completely, preventing any light from passing through.
Examples include cardboard and thick cloth.
Shadow Formation
A shadow is a dark region formed when an object blocks light from reaching a surface.
Conditions for Shadow Formation
Shadows require three components:
A light source (e.g., Sun or torch),
An opaque or partially opaque object to block the light,
A screen (e.g., wall, floor, or ground) where the shadow appears.
Types of Shadows
Opaque objects create the darkest, most defined shadows.
Translucent objects produce lighter, less distinct shadows.
Transparent objects may create faint shadows or none at all.
Shadow Characteristics and Observations
From the above observations we can conclude:
Shadows are formed when an opaque object blocks light from reaching a surface, which acts as a screen.
To observe a shadow, we need a light source, an opaque object, and a screen.
The size, shape, and clarity of the shadow depend on the positions of the object, light source, and screen.
Changing the colour of the object does not affect the colour of the shadow.
Shadows help us understand the presence and shape of objects but do not reveal their colour.
Fascinating Facts
Shadow play, or shadow puppetry, is an ancient art where flat cut-out puppets are placed between a light source and a screen to create lifelike movements.
Different Indian regions have unique styles like Charma Bahuli Natya (Maharashtra), Keelu Bomme and Tholu Bommalata (Andhra Pradesh), Togalu Gombeyaata (Karnataka), Ravana Chhaya (Odisha), Tholpavakoothu (Kerala), and Bommalattam (Tamil Nadu).
These performances entertain and convey important community messages.
Try yourself:
What type of materials allows light to pass through almost completely?
A.Opaque materials
B.Transparent materials
C.Translucent materials
D.Reflective materials
View Solution
Reflection of Light
Reflection occurs when light bounces off a surface, changing its direction.
Reflection by Shiny Surface
Shiny surfaces, such as polished steel plates or plane mirrors, reflect light efficiently, creating bright spots on nearby surfaces.
For example, tilting a mirror can direct sunlight onto walls not directly lit.
When a light beam hits a plane mirror, it changes direction as a reflected beam, which is why mirrors are used to redirect light in many applications.
Images Formed in a Plane Mirror
A plane mirror is a flat mirror that forms a virtual image of an object placed in front of it.
Image Characteristics
Same Size: The image is the same size as the object.
Erect: The image is upright, with the top of the object appearing at the top.
Laterally Inverted: The left side of the object appears as the right side in the image, and vice versa For example: raising your left arm makes the image raise its right arm). This is called lateral inversion.) Another example: word “AMBULANCE” is written in reverse letters on the front of ambulances so that drivers in vehicles ahead can see the word correctly in their rear-view mirrors. This helps them quickly recognize an approaching ambulance and give way.
Distance Relationship: The image’s distance from the mirror equals the object’s distance from the mirror. Moving closer to the mirror makes the image appear closer, and moving farther makes it appear farther.
Fascinating Fact
The exact time when mirrors were invented is unknown. Early mirrors were made by polishing stone or metal. With the invention of glass mirrors, the traditional art of making metal mirrors faded but still survives in places like Kerala, where the unique Aranmula Kannadi metal mirror has been crafted for centuries.
Pinhole Camera
A pinhole camera is a simple device that uses a tiny hole to form an image on a screen.
Working Principle
Light rays from an object pass through a small hole (pinhole) and form an inverted (upside-down) image on a screen, such as tracing paper. The image shows the object’s colors but is reversed vertically.
Making a pinhole cameraA sliding pinhole camera
Use two cardboard boxes, one slightly smaller to slide inside the other.Make a small hole in one side of the larger box.
Cut a square on the opposite side of the smaller box and cover it with thin translucent paper (like tracing paper) to act as a screen.
Slide the smaller box inside the larger one so the tracing paper is inside.
Point the pinhole side towards a distant object in bright sunlight.
Look through the open side, cover your head and camera with a dark cloth to see the image clearly.
Adjust the smaller box forward or backward until the image appears on the tracing paper.
Try yourself:
What is a characteristic of the image formed by a plane mirror?
A.It is always larger than the object.
B.It is the same size as the object.
C.It is always smaller than the object.
D.It is always distorted.
View Solution
Characteristics of Image Formed
The image formed on the tracing paper is upside down (inverted).
The images show the colours of the objects on the other side.
Dive Deeper
A pinhole camera forms an upside-down image, while a mirror produces a laterally inverted image that is not upside down. These concepts will be explored further in higher grades.
Making Some Useful Items
The properties of light, such as its straight-line travel and reflection, are used to create practical devices.
Periscope
A simple periscope is made by placing two plane mirrors inside a Z-shaped box.
The reflection from these mirrors allows us to see objects that are not directly visible.
Periscopes are commonly used in submarines, tanks, and by soldiers to see outside their bunkers. You can also use one to see over taller people.
A Periscope
Kaleidoscope
A kaleidoscope is made by joining three rectangular plane mirrors in a triangular shape and placing them inside a circular tube.
Colored pieces like broken bangles or beads are placed on one end, covered with a transparent sheet and tracing paper.
Looking through the open end shows beautiful, ever-changing patterns due to multiple reflections from the three mirrors.
Artists often use kaleidoscopes to find inspiration for new designs.
A kaleidoscope
Difficult Words
Luminous Objects: Objects that emit their own light, such as the Sun, stars, or fireflies.
Non-Luminous Objects: Objects that do not emit light but reflect light from other sources, such as the Moon or a mirror.
Rectilinear Propagation: The property of light traveling in a straight line.
Transparent Materials: Materials that allow light to pass through almost completely, like glass.
Translucent Materials: Materials that allow light to pass through partially, causing diffused visibility, like tracing paper.
Opaque Materials: Materials that block light completely, like cardboard.
Shadow: A dark region formed when an object blocks light from reaching a surface.
Reflection: The change in direction of light when it bounces off a surface, such as a mirror.
Lateral Inversion: The left-right reversal of an image in a plane mirror, where the left side appears as the right side.
Pinhole Camera: A device that uses a tiny hole to form an inverted image of an object on a screen.
Periscope: A device with two plane mirrors that allows viewing of objects not directly visible, used in submarines and bunkers.
Kaleidoscope: A device with three mirrors forming symmetrical patterns from reflected objects, used for design inspiration.
All living beings grow and need food for their growth. While animals eat food to grow, what about plants? Have you ever seen plants eating like animals? As animals grow, their size and weight increase, and their bodies change. What changes do you notice in plants as they grow? Food provides nutrients like carbohydrates, fats, proteins, vitamins, and minerals, along with water, all essential for growth.
Let’s explore how plants obtain these nutrients for their growth.
How Do Plants Grow?
Plant growth involves visible changes such as the emergence of new leaves and branches, increased height, and a thicker stem.
These changes occur as plants obtain essential resources like water, sunlight, and nutrients from their environment.
Role of Sunlight and Water
Sunlight provides energy for food production, while water is crucial for nutrient transport and maintaining plant structure.
Plants grown with both sunlight and water show better growth, with more leaves, greater height, and vibrant green leaves, compared to those lacking either resource.
For instance, a plant without water may wilt or die, and one without sunlight may have pale or yellow leaves due to reduced food production.
Fascinating Fact The ancient Indian text Vrikshayurveda states, “Trees do not produce fruits and flowers merely because they are planted.” This text contains valuable observations about plant growth, soil, and farming methods to improve crop health and yield. Based on practical experience and long-term patterns, it systematically guides agricultural practices. For example, it describes ways to prepare organic manure using water, barley, and seeds like green gram, black gram, and horse gram.
Try yourself:
What do roots absorb from the soil for plant growth?
A.Carbon dioxide and chlorophyll
B.Fruits and flowers
C.Sunlight and air
D.Water and minerals
View Solution
How Do Plants Get Food for Their Growth?
Unlike animals, plants produce their own food through a process called photosynthesis, primarily in their leaves. This food, stored as starch (a carbohydrate), provides energy and building blocks for growth.
Leaves: The ‘Food Factories’ of Plants
Leaves are the primary sites for food production due to their broad, flat structure and the presence of chlorophyll, a green pigment that captures sunlight. Chlorophyll enables leaves to convert sunlight, water, and carbon dioxide into food.
Starch Production
Leaves store food as starch, a carbohydrate.
The presence of starch can be confirmed by an iodine test, where a leaf turns blue-black if starch is present.
This indicates that the leaf has produced food.
Dive Deeper
Decolourisation of a leaf in the beginning of testing enables us to easily observe colour change and, thus, the presence of starch.
Fascinating Facts
Some plant leaves look red, violet, or brown because they have more colored pigments than green chlorophyll, which hides the green color. Some of these pigments also assist in photosynthesis. You can perform an iodine test on such leaves to detect starch, which shows that photosynthesis has occurred.
Chlorophyll
Leaves have green and non-green patches due to the presence or absence of chlorophyll.
Starch is produced only in the green parts of the leaf where chlorophyll is present.
Non-green patches usually lack sufficient chlorophyll and do not produce detectable starch.
The presence of starch can be confirmed by performing an iodine test, where starch turns blue-black.
Leaves exposed to sunlight produce starch, while leaves kept in darkness do not, even if they have green patches.
This shows that chlorophyll, in the presence of sunlight, is essential for the preparation of starch in plants.
Because leaves produce food through this process, they are often called the “food factories” of plants.
Try yourself:
What is the primary function of chlorophyll in plants?
A.Captures sunlight for photosynthesis
B.Stores food as starch
C.Produces oxygen during respiration
D.Absorbs water from the soil
View Solution
Role of Air in Food Preparation
Air, specifically carbon dioxide, is a key component in photosynthesis. Plants take in carbon dioxide from the air to produce food.
Carbon Dioxide Requirement
Carbon dioxide from the air is essential for plants to prepare food (starch).
When a leaf is kept in an environment without carbon dioxide, starch is not produced in that part.
This shows that carbon dioxide is a key ingredient required for photosynthesis.
Oxygen Release During Photosynthesis
During photosynthesis, plants release oxygen gas.
Oxygen production is evident when plants are exposed to sunlight, and bubbles of oxygen can be observed.
The release of oxygen confirms that photosynthesis happens only in the presence of sunlight.
Activity showing the release of oxygen during photosynthesis
Photosynthesis: In a Nutshell
Photosynthesis is the process by which plants use sunlight, chlorophyll, carbon dioxide, and water to produce glucose (a simple carbohydrate) and oxygen.
Glucose serves as an immediate energy source and can be converted into starch for storage.
The word equation for photosynthesis is:
Oxygen is released as a by-product, which is vital for the survival of other living beings.
Photosynthesis occurs mainly in leaves but also in other green parts of the plant containing chlorophyll.
Know A Scientist: Rustom Hormusji Dastur
Many scientists worldwide have contributed to understanding photosynthesis. In India, Rustom Hormusji Dastur (1896–1961) was a notable plant scientist who studied this process. He served as the head of the Botany Department at the Royal Institute of Science, Bombay (now the Institute of Science, Mumbai) from 1921 to 1935. Dastur researched how factors like water availability, temperature, and light color affect photosynthesis, highlighting their importance in the process.
How Do Leaves Exchange Gases During Photosynthesis?
Leaves have tiny pores called stomata on their surface, which facilitate the exchange of gases during photosynthesis and respiration.
These pores allow carbon dioxide to enter the leaf for photosynthesis and oxygen to exit as a by-product.
Stomata also play a role in respiration by allowing oxygen intake and carbon dioxide release.
Stomata
Transport in Plants
Plants have a transport system to move water, minerals, and food to different parts, ensuring growth and survival. Roots absorb water and minerals from the soil, which are transported to other parts of the plant through specialized tissues called Xylem.
All living beings need water to grow, and plants use water for photosynthesis.
Water and minerals from the soil are absorbed by the roots of plants.
Minerals are essential nutrients for plant growth.
Water and minerals travel from the roots to other parts of the plant through a tissue called xylem.
The xylem consists of thin tube-like structures in stems, branches, and leaves that carry water and dissolved minerals upward.
The movement of water and minerals can be demonstrated by placing plant twigs in colored water, where the color travels up the stem and into leaves and flowers.
Water transported through the xylem supports various functions in the plant.
Transport of Food
Food produced in the leaves (glucose or starch) is distributed to non-green parts of the plant, such as roots, stems, and fruits, for growth and storage, through specialized tissue called phloem
Leaves are the primary site of photosynthesis, where food is prepared.
The phloem is vascular tissue that transports food from the leaves to other parts of the plant.
This ensures that areas not involved in photosynthesis, like roots and developing fruits, receive the energy and nutrients they need.
Some of this transported food is stored in other parts of the plant, such as seeds and roots.
Try yourself:
What is the function of stomata in leaves?
A.Produce glucose
B.Exchange gases
C.Transport water
D.Store starch
View Solution
Do Plants Respire?
Plants, like animals, respire to produce energy for growth and other functions. Respiration occurs in all parts of the plant, whether green or non-green.
During respiration, plants break down glucose using oxygen, releasing carbon dioxide, water, and energy. The word equation for respiration is: Glucose + Oxygen → Carbon dioxide + Water + Energy
The energy released supports processes like growth, cell repair, and nutrient transport.
An experiment with soaked moong bean seeds shows that carbon dioxide is released during respiration, which turns lime water milky.
This carbon dioxide comes from the seeds respiring inside the flask.
The energy produced in respiration is used by plants for growth and development.
All parts of the plant, whether green or non-green, carry out respiration.
Plants have distinct processes for synthesizing food (photosynthesis), transporting food, and using it to produce energy (respiration).
Respiration in Plants
Terms to Remember
Photosynthesis: The process by which plants use sunlight, chlorophyll, carbon dioxide, and water to produce glucose and oxygen.
Chlorophyll: A green pigment in leaves that captures sunlight for photosynthesis.
Stomata: Tiny pores on leaf surfaces that allow gas exchange (carbon dioxide in, oxygen out) during photosynthesis and respiration.
Xylem: Vascular tissue that transports water and minerals from roots to other parts of the plant.
Phloem: Vascular tissue that transports food (glucose or starch) from leaves to other parts of the plant.
Respiration: The process by which plants break down glucose using oxygen to release energy, carbon dioxide, and water.
Glucose: A simple carbohydrate produced during photosynthesis, used as an energy source or stored as starch.
Starch: A carbohydrate stored in plants, produced from glucose during photosynthesis.
Life processes like nutrition, respiration, excretion, and reproduction are essential for the survival of all living beings.
Animals eat different types of food based on their needs:
Bees and sunbirds suck nectar from flowers.
Human and animal infants feed on mother’s milk.
Snakes swallow their prey whole.
Some aquatic animals filter tiny food particles from water.
Animals obtain energy from food to carry out life processes.
Food contains complex components like carbohydrates, proteins, and fats, which must be broken down into simpler forms to be used by the body.
This breakdown happens in a long tube called the alimentary canal, which starts at the mouth and ends at the anus.Human Digestive System
Digestive juices secreted at various points in the alimentary canal help break down food.
The simpler food is absorbed and transported to different body parts for various functions.
Nutrition in Animals
Complex food components must be broken down into simpler forms before the body can use them. This breakdown process is called digestion. Digestion occurs in different ways across animals depending on their type and structure.
To understand digestion better, we first study how it happens in humans.
Digestion in Human Beings
Digestion is the process of breaking down complex food into simpler substances. It occurs in the alimentary canal, a long tube from the mouth to the anus.
Beginning with the mouth cavity
Digestion begins in the mouth, where food enters and is broken down into smaller pieces by teeth through crushing and chewing. This is called mechanical digestion.
When you think of your favorite food, your mouth produces more saliva, which moistens the food.
Saliva contains digestive juices that start breaking down starch (a carbohydrate) into sugar, which is why starchy foods like chapati or rice taste sweet when chewed for some time.
Science and Society
A healthy mouth requires good oral hygiene. We should brush our teeth and clean our tongue twice a day, and rinse our mouth with water after each meal to prevent tooth decay and bad smell in the mouth. Find out the ways our elders were maintaing oral hygiene.
Activity to Investigate Saliva’s Role
Aim: To observe the effect of saliva on the breakdown of starch in boiled rice.
Materials Needed: Two test tubes ,Teaspoon, Boiled rice , Water and Iodine solution
Procedure:
Label the test tubes as ‘A’ and ‘B’.
Place one teaspoonful of boiled rice in test tube A and a teaspoonful of chewed boiled rice in test tube B.
Add 3–4 mL of water to both test tubes.
Note the initial colour of the rice-water mixture.
Add 3–4 drops of iodine solution to each test tube and mix the contents.
Observe the colour changes in both test tubes.
Observations:
In test tube A, the boiled rice may turn blue-black, indicating the presence of starch.
In test tube B, the chewed rice may not change colour or show a very light blue-black colour, indicating the breakdown of starch into simpler sugars.
2. Food pipe (Oesophagus): A passage from the mouth to the stomach
After chewing, saliva moistens the food, making it soft and easy to swallow.
The tongue mixes the chewed food with saliva and pushes it into the food pipe or oesophagus.
The oesophagus is a long, flexible tube connecting the mouth to the stomach.
Food moves down the oesophagus by a wave-like motion called peristalsis, where the walls of the food pipe contract and relax gently.Movement of food in the food pipe
This movement continues throughout the alimentary canal, pushing food forward for digestion.
3. Stomach
The walls of the stomach contract and relax to churn the food, mixing it thoroughly.
The stomach lining secretes digestive juice, acid, and mucus.
Digestive juice breaks down proteins into simpler components.
The acid helps in protein digestion and kills harmful bacteria.
Mucus protects the stomach lining from being damaged by the acid.
Food is partially digested in the stomach and turned into a semi-liquid mass, ready for the next stage of digestion.
Fascinating Facts
In 1822, Alexis St. Martin was accidentally shot in the stomach, leaving a small permanent hole after treatment.
Dr. William Beaumont, his doctor, used this opening to directly observe digestion in the stomach.
Beaumont conducted experiments to study how different foods are broken down.
He also explored how emotions can affect the process of digestion.
This accidental discovery significantly advanced our understanding of stomach function.
Try yourself:
What begins the process of digestion in humans?
A.Oesophagus
B.Anus
C.Mouth
D.Stomach
View Solution
4. Small Intestine
After leaving the stomach, partially digested food enters the small intestine, which is about 6 meters long, making it the longest part of the alimentary canal.Alimentary canal if it is stretched out
The small intestine receives digestive secretions from:
Its own inner lining.
The liver, which produces bile.
The pancreas, which produces pancreatic juice.
Bile is mildly basic; it neutralizes stomach acid and breaks fats into tiny droplets, aiding digestion.
Pancreatic juice is also basic and helps neutralize acid, while breaking down carbohydrates, proteins, and fats.
Digestive juices from the small intestine further break down fats, proteins, and carbohydrates into simpler forms.
Nutrients are absorbed into the blood through the inner lining of the small intestine.
The lining has thousands of finger-like projections called villi, which increase the surface area for efficient absorption.
Absorbed nutrients provide energy, help growth and repair, and support body functions.
Science and Society
Celiac disease is a condition where the body reacts to gluten, a protein found in wheat, barley, and rye.
This reaction damages the inner lining of the small intestine, impairing nutrient absorption.
As a result, the small intestine cannot function properly.
The only way to manage celiac disease is to avoid gluten-containing foods.
Millets such as jowar, bajra, and ragi are good alternatives because they are naturally gluten-free.
5. Large Intestine
After nutrient absorption in the small intestine, undigested food moves into the large intestine.
The large intestine is about 1.5 meters long, shorter but wider than the small intestine.
Its main function is to absorb water and some salts from the undigested food.
This process turns the waste into a semi-solid form called stool.
Stool is stored in the rectum until the body is ready to eliminate it.
The waste is expelled through the anus in a process called egestion.
Eating fiber-rich foods like fruits, vegetables, and whole grains helps keep the large intestine healthy and stool easier to pass.
Fascinating Facts
The large intestine contains helpful bacteria that break down undigested fiber.
These bacteria produce nutrients important for health.
Eating fiber-rich and fermented foods like curd and pickles supports a healthy digestion.
Science and Society
The ancient Ayurvedic text Charaka Samhita stresses the importance of easily digestible foods.
Spices like ginger, black pepper, and cumin are used to improve digestion.
Modern nutrition also highlights eating at proper times, mindful eating, and avoiding overeating to maintain good digestive health.
Digestion in Other Animals
Not all animals digest food like humans. Their digestive systems are adapted to their diets and habitats:
Ruminants
These grass-eating animals, partially chew it, and swallow it into their stomachs for partial digestion.
The food is then brought back to the mouth for thorough chewing, a process called rumination.
Ruminants spend about 8 hours a day chewing their food.
After chewing, the food moves down the alimentary canal for further digestion.
Birds
Birds lack teeth but have a special stomach chamber called the gizzard.
The gizzard breaks down food by contracting and relaxing, often with the help of small stones (grit) swallowed by birds.
Animals show variations in their digestive systems to suit different types of food.
Nutrients from digested food help build and repair the body or are broken down to release energy.
The process of converting nutrients into energy is called respiration.
Try yourself:
What is the primary function of bile produced by the liver?
A.To neutralize stomach acids
B.To produce digestive juices
C.To break down carbohydrates
D.To absorb nutrients
View Solution
Respiration in Animals
Respiration is the process by which animals use oxygen to break down nutrients (like glucose) to release energy, producing carbon dioxide and water as by-products.
Breathing, a physical process, brings oxygen into the body and removes carbon dioxide, while respiration is a chemical process occurring in cells.
Respiration in Humans
Breathing is the process of inhaling (breathing in) oxygen and exhaling (breathing out) carbon dioxide.
Breathing is essential for survival; without it, humans cannot live more than a few minutes.
All living beings, including plants and animals, breathe.
The respiratory system is the body system responsible for breathing and gas exchange.
Human Respiratory System
Nostrils: Openings in the nose through which air is inhaled and exhaled.
Nasal Passages: Small passages after the nostrils lined with tiny hairs and mucus that trap dust and dirt. Breathing through the nose is better than through the mouth because of this filtration.
Windpipe (Trachea): Tube that carries air from the nasal passages to the lungs and divides into two branches.
Lungs and Alveoli: The windpipe branches further inside the lungs into finer tubes ending in tiny balloon-like sacs called alveoli, where gas exchange occurs.
Protection: The lungs are protected by the rib cage, a bony structure surrounding them.
Science and Society
Although the respiratory system filters out much dust from inhaled air, small infectious particles can still enter the lungs.
For example, during the COVID-19 pandemic, the SARS-CoV-2 virus affected the respiratory system.
This virus caused breathing difficulties and serious lung problems in many people.
Activity: Understanding Breathing Mechanism through a Simple Model
Materials Needed: Wide transparent plastic bottle with a lid (bottom removed) , Y-shaped hollow tube, Deflated balloons (2), Rubber bands, Clay (for sealing) , Thin rubber sheet ,Large rubber band (for securing rubber sheet).
Procedure
Prepare the Bottle:
Take the wide transparent plastic bottle and remove its bottom.
Make a hole in the lid of the bottle.
Prepare the Tube and Balloons:
Take the Y-shaped hollow tube. Fix the two deflated balloons to the forked end of the tube and secure them with rubber bands to make them airtight.
Assemble the Model:
Insert the straight end of the tube tightly through the lid of the bottle and seal the lid with clay to ensure it is airtight.
Attach a thin rubber sheet to the open base of the bottle tightly using a large rubber band.
Conducting the Experiment:
Pulling the Rubber Sheet Downward: Pull the rubber sheet from the center of the base downwards. Observe the balloons closely.
Releasing the Rubber Sheet: Release the rubber sheet upwards and observe the changes in the balloons. Model of Mechanism of Breathing
Observations:
When you pull the rubber sheet downwards, the balloons inflate.
Conversely, when you release the rubber sheet upwards, the balloons deflate.
Process of Respiration Involves:
(i) Inhalation
When you breathe in (inhale), your chest expands as your ribs move up and outwards.
The diaphragm, which is a dome-shaped muscle located below your lungs, moves downwards during inhalation.
This movement increases the space inside your chest, allowing air to enter your lungs.
(ii) Exhalation
When you breathe out (exhale), your ribs move down and inwards, while the diaphragm moves upwards.
This reduces the space inside your chest and helps to push air out of your lungs.
In the activity we discussed before, the balloons represent the lungs, and the rubber sheet represents the diaphragm.
Science and Society
Breathing exercises like Pranayama and Tummo have been practiced for centuries worldwide to boost lung health and mental calmness. Pranayama from India enhances respiration and concentration, while Tummo breathing in cold Ladakh improves lung function and body warmth. Deep breathing combined with chanting is also used in many traditions to promote relaxation and clarity of mind.
Try yourself:
What is the first part of the respiratory system where air enters the body?
A.Nostrils
B.Windpipe
C.Alveoli
D.Lungs
View Solution
What do we Breathe Out?
When we exhale, the air we breathe out contains more carbon dioxide compared to the air we inhale.
This can be demonstrated through an experiment with lime water.
Lime water is a clear solution that turns milky when it reacts with carbon dioxide.
Two test tubes with equal amounts of fresh lime water are taken.(a) Air is passed into lime water with a pichkari/syringe (b) Air is exhaled into lime water
Air similar to inhaled air is passed through lime water in test tube A using a syringe.
Exhaled air is blown through a straw into lime water in test tube B.
Test tube B (exhaled air) turns milky, showing a reaction with carbon dioxide.
Test tube A (inhaled air) shows no change and remains clear.
This indicates exhaled air contains a higher concentration of carbon dioxide than inhaled air.
(ii) Gas Exchange
Fresh air enters the lungs through breathing and fills tiny sacs called alveoli.
Alveoli have thin walls surrounded by blood vessels.
Carbon dioxide from the blood is released into the alveoli to be exhaled.
Oxygen from the alveoli passes into the blood and is carried to the entire body.
Oxygen is used to break down glucose from food, releasing energy in a process called respiration.
Gas exchange through alveoli
Overall Process of Respiration: In cells, oxygen breaks down glucose to release energy, carbon dioxide, and water. Glucose + Oxygen → Carbon dioxide + Water + Energy
Inhaled air contains about 21% oxygen and 0.04% carbon dioxide.
Exhaled air contains about 16–17% oxygen and 4–5% carbon dioxide.
Breathing is a physical process of air intake and release.
Respiration is a chemical process inside the body that produces energy.
Both breathing and respiration are vital for survival.
The percentage of oxygen and carbon dioxide in inhaled and exhaled air
Difference Between Breathing and Respiration
Role of the Circulatory System
The circulatory system transports nutrients, oxygen, and waste products in the body.
It consists of the heart, blood, and blood vessels.
The heart pumps blood through vessels to deliver oxygen and nutrients and remove wastes.
Science and Society
Smoking damages the lungs and increases the risk of lung cancer and other respiratory diseases.
It causes persistent coughing and makes the body prone to frequent infections.
Smoking releases toxic chemicals into the air, harming others through passive smoking.
Children, pregnant women, and the elderly are especially vulnerable to passive smoking.
Avoiding smoking protects both personal health and the health of those around us.
Respiration in Other Animals
Different animals live in different habitats and have different breathing mechanisms suited to their environments.
Animals have adapted respiratory systems based on their habitats:
Lungs: Animals like birds, elephants, lions, cows, lizards, and snakes breathe through lungs, though lung structures vary.
Gills: Aquatic animals like fish use gills, which extract dissolved oxygen from water and release carbon dioxide.
Breathing body parts in a fish
Skin and Gills: Amphibians like frogs use gills as tadpoles, lungs as adults on land, and moist skin for gas exchange in water.
Moist Skin: Earthworms breathe through their moist skin, allowing oxygen and carbon dioxide exchange.
Try yourself:
What happens to lime water when exhaled air is passed through it?
A.It turns milky
B.It remains clear
C.It changes color
D.It bubbles
View Solution
Terms to Remember
Alimentary Canal: The long tube in the digestive system from the mouth to the anus where food is digested and absorbed.
Mechanical Digestion: The physical breakdown of food into smaller pieces, such as by chewing.
Peristalsis: The wave-like muscle contractions that move food through the digestive system.
Villi: Finger-like projections in the small intestine that increase surface area for nutrient absorption.
Egestion: The process of expelling undigested waste (stool) through the anus.
Ruminants: Animals like cows that partially digest food, regurgitate it, and chew it again.
Gizzard: A muscular chamber in birds that grinds food, often with swallowed stones.
Alveoli: Tiny air sacs in the lungs where oxygen and carbon dioxide are exchanged.
Diaphragm: A dome-shaped muscle below the lungs that aids breathing by moving up and down.
Respiration: The chemical process in cells where oxygen breaks down glucose to release energy.
Circulatory System: The system (heart, blood, blood vessels) that transports nutrients, oxygen, and waste.
Prerna and her sister were watching a sports channel. Prerna loved running and was the fastest girl in her district’s 100 metre sprint. She was now training for the state level and dreamed of running for India. Watching old Olympic races, Prerna was amazed at how exact the timing was, even when runners finished together. At school, they used a stopwatch to time races.
Her mother wore a watch, her sister checked time on a phone, and her uncle had a Braille and a talking watch. There was also a big clock at school. Prerna wondered how people in the past told time without these devices.
Let’s explore the history of time and learn more about how people have measured it over the ages.
Measurement of Time
Long ago, humans became interested in keeping track of time. They noticed many natural events happened in regular cycles—like the Sun rising and setting, the phases of the Moon, and changing seasons. These cycles helped people create calendars. A day was defined by the cycle of the Sun rising and setting.
Next, people wanted to know the time during the day. Since there were no clocks or watches, they invented devices to measure smaller parts of the day, such as:
To measure time within a day, they invented devices such as:
Sundials: These used the shadow cast by the Sun’s light on an object to show the time of day. As the Sun moved, the shadow’s position changed.
Water Clocks: These measured time using water flow. One type had water flowing out of a marked vessel, while another used a bowl with a hole that sank when filled with water.
Hourglasses: These used sand flowing from one bulb to another to measure time.
Candle Clocks: These were candles with markings that showed time as they burned down.
Fascinating Facts
The world’s largest stone sundial, called the Samrat Yantra, was built about 300 years ago at the Jantar Mantar in Jaipur, Rajasthan. This site is a UNESCO World Heritage place with many ancient astronomical instruments.
The Samrat Yantra stands 27 metres tall. Its shadow moves very slowly—about 1 millimetre every second—and falls on a scale that can measure time as precisely as every 2 seconds. Like all sundials, it shows local solar time, so a small correction is needed to convert this to Indian Standard Time.
Should we make a simple water clock? Let’s us Construct
A water clock is a device that measures time by the flow of water from one container to another. It works on the principle of constant water flow, where the time taken for a certain amount of water to flow from the upper part to the lower part indicates the passage of time.
Materials Required
Used transparent plastic bottle (1/2 litre or larger) with cap
Drawing pin
Water
Ink or food colour (optional)
Procedure
Prepare the Bottle: Cut the plastic bottle into two halves roughly in the middle.
Make a Hole: Use a drawing pin to make a small hole in the cap of the bottle.
Assemble the Clock: Place the upper part of the bottle (with the hole in the cap) upside down on the lower half.
Fill with Water: Fill the upper part of the bottle with water. You can add a few drops of ink or colour to make the water level more visible.
Start the Clock: The water will start dripping into the lower part of the bottle. Use a watch to mark the water level at one-minute intervals until all the water has dripped down.
How to Use the Water Clock
Resetting: Pour the water from the lower part back into the upper part.
Timing: Watch the water drip into the lower part and mark each time it reaches a level you previously marked. Each mark indicates that one more minute has passed.
Fascinating Facts
In ancient India, time was measured using shadows and water clocks.
The earliest mention of measuring time by shadows comes from the Arthashastra by Kautilya (2nd century BCE to 3rd century CE).
Around 530 CE, Varahamihira gave a precise way to calculate time using the shadow of a vertical stick.
Water clocks, where water flowed out of a vessel, were also described in ancient texts like the Arthashastra and Sardulakarnavadana.
These early water clocks were not very accurate because the flow of water slowed as the water level dropped.
To solve this, the sinking bowl water clock (called Ghatika-yantra) was developed and mentioned by Aryabhata and other astronomical texts.
The Ghatika-yantra was used continuously in Buddhist monasteries, royal palaces, and town squares. When the bowl sank, time was announced by drums, conch shells, or gongs.
Although pendulum clocks replaced the Ghatika-yantra by the late 19th century, it was still used in religious places for rituals.
As human civilization advanced and long-distance travel became common, measuring time precisely became very important. This led to the development of mechanical clocks driven by weights, gears, and springs starting from the 14th century.
The invention of the pendulum clock in the 17th century was a major breakthrough, significantly improving the accuracy of mechanical timekeeping.
Know a Scientist: Galileo Galilei
The pendulum clock was invented in 1656 and patented in 1657 by Christiaan Huygens (1629–1695). He was inspired by the earlier work of Galileo Galilei(1564–1642).Huygens’ Pendulum clock
Galileo noticed a lamp swinging back and forth in a church. Using his own pulse to measure time, he found that the lamp took the same amount of time for each swing. After testing different pendulums, Galileo discovered that the time for one complete swing stayed the same for a pendulum of a fixed length.
This discovery helped Huygens create the accurate pendulum clock.
Try yourself:What device measures time using the flow of water?
A.Candle Clock
B.Hourglass
C.Sundial
D.Water Clock
View Solution
The Simple Pendulum
A simple pendulum consists of a small metal ball, known as the bob, which is suspended from a rigid support by a long thread.A simple pendulum
When the bob is at rest, it is in the mean position. If the bob is moved slightly to one side and released, it begins to swing back and forth in an oscillatory motion.
This motion is periodic because it repeats the same path after a fixed interval of time.
One complete oscillation of the pendulum occurs when the bob, starting from the mean position O, moves to the extreme position A, changes direction, moves to another extreme position B, changes direction again, and returns to O.
Alternatively, the pendulum also completes one oscillation when the bob moves from one extreme position A to another extreme position B and then comes back to A.
The time taken for the pendulum to complete one oscillation is called its time period.
Experiment to Measure the Time Period of a Pendulum
Materials Needed:
A piece of string about 150 cm long
A heavy metal ball or stone (bob)
A stopwatch or watch to measure time
A ruler to measure length
Procedure:
Tie the bob to one end of the string.
Fix the other end of the string to a rigid support so that the length between the support and the bob is about 100 cm.
Let the bob come to rest in its mean position. Your pendulum is now ready.
Gently hold the bob, pull it slightly to one side, and release it without pushing. Make sure the string is taut when you release it.
Observe the pendulum oscillating back and forth.
Using the watch, measure the time taken for the pendulum to complete 10 oscillations.
Record the time in a table. Repeat this measurement 3 to 4 times for accuracy.
Calculate the time period by dividing the total time for 10 oscillations by 10.
Observations
Length of the string = 100 cm
The time period of the pendulum is nearly consistent with each measurement.
This indicates that the time taken for one complete oscillation of the pendulum remains fairly constant.
Conclusion: The pendulum’s time period stays nearly constant because its length and gravity remain unchanged. This makes its swings stable and reliable for measuring time.
Think Like A Scientist
When experimenting with pendulums using a watch, the following questions can be investigated:
How does the length of the pendulum affect its time period?
Do pendulums of different lengths have different time periods?
Does the mass of the bob affect the time period?
To test these questions:
Use the same bob and measure the time period of pendulums with two or three different lengths.
Observe whether the time period changes with length and record the results.
Keep the pendulum length fixed and test with bobs of different masses to check if mass influences the time period.
Conclusion:
The time period of a simple pendulum depends on its length but not on the mass of the bob. At a given location, all pendulums of the same length have the same time period.
All clocks, whether ancient or modern, rely on a process that repeats continuously to mark equal intervals of time.
Dive Deeper
Modern clocks measure time using repeating movements, but instead of pendulums, they use tiny vibrations from quartz crystals or atoms. Early pendulum clocks could lose or gain 10 seconds every day, but today’s atomic clocks are very accurate and lose only one second in millions of years. Scientists keep working to make clocks even better.
SI Unit of Time
The standard unit of time in the International System of Units (SI) is the second, represented by the symbol “s.”
Larger units of time include the minute (symbol: “min”. and the hour (symbol: “h” ).
The conversions between these units are as follows:
Dive Deeper
Units of time like second, minute, and hour start with a lowercase letter, unless they begin a sentence. Their symbols — s, min, and h — are always lowercase and singular. Do not put a full stop after the symbol unless it is at the end of a sentence. Always leave a space between the number and the unit when writing time. Also, using “sec” for second or “hrs” for hour is incorrect.
Fascinating Facts
The hole in the bowl of the Ghatika-yantra was designed so it took 24 minutes to fill and sink. This time unit was called a ghatika or ghati. It became the standard way to measure time and was used until the end of the 19th century. A 24-hour day was divided into 60 equal ghatis.
Science and Society: Precision in Time Measurement
In modern society, measuring very small fractions of a second is crucial in various fields:
Sports: Timekeeping devices can record events to one-hundredth or one-thousandth of a second to determine race winners.
Medicine: Heart monitors like Electrocardiogram (ECG) machines measure heartbeat variations in milliseconds to identify health issues.
Music: Digital recordings capture sound thousands of times per second for smooth playback.
Technology: Smartphones and computers process signals in microseconds, enabling fast operation.
As clocks become faster and more accurate, they contribute to society in ways that may not be immediately noticeable.
Try yourself:
What is the mean position of a simple pendulum?
A.The position when the bob is at its highest point
B.The position when the bob is moving to one side
C.The position when the bob is at rest
D.The position when the pendulum is swinging
View Solution
Slow or Fast
When we say something is moving fast or slow, we compare how far it moves in a certain amount of time.
For example, in a 100-metre race, all runners start together but soon spread out.Boys running a race on a straight track
The runner who is ahead at a given moment has covered more distance in the same time and is running faster.
Therefore, the distance covered in a given time helps decide who is faster or slower.
We say that the faster runner has a higher speed.
Speed
Speed is the measure of how fast an object is moving. It tells us the distance an object covers in a certain amount of time.
By comparing the distances moved by two or more objects in a unit time, it can be determined which object is moving faster.
The unit time can be one second, one minute, or one hour.
The distance covered by an object in a unit time is called its speed.
The SI unit of speed is metre per second (m/s), based on the SI units of distance (metre) and time (second). For larger distances and times, speed is often measured in kilometre per hour (km/h).
Example: Ravi’s school is 5.2 km from his house. It took him 20 minutes to reach his school riding on his bicycle. Calculate the speed of the bicycle in m/s.
Solution: Speed of the bicycle = Distance covered/ Time Taken Speed = 5.2 km/20 min Convert the units = 5.2 x 1000 m / 20 x 60 s = 5200m/1200s = 4.33 m/s Answer: The speed of the bicycle is 4.33 m/s.
Activity: To compare the speeds of different trains based on their timetable information.
Calculate speed for each train
Comparison
Fastest Train: The Superfast Train between Station G and Station H is the fastest, with a speed of 150 km/h.
Slowest Train: The Passenger Train between Station A and Station B has the slowest speed of 48.19 km/h.
Relationship betwen speed, distance and time
We know the formula to calculate speed is:
This formula can be rearranged to find distance if speed and time are known:
Similarly, to find time if distance and speed are known:
Example 2: Question: Priya is traveling to a nearby town in a car moving at a speed of 60 km/h. If it takes her 3 hours to reach the town, how far is the town?
Solution: Distance covered by the car = Speed × Time = 60 km/h × 3 h = 180 km
Answer: The town is 180 km away.
Example 3:
Question: A train is traveling at a speed of 80 km/h. How much time will it take to cover a distance of 240 km?
Solution: Time taken by the train = Distance covered / Speed = 240 km / 80 km/h = 3 h
Answer: The train will take 3 hours to cover 240 km.
Average Speed
The speed calculated by dividing total distance by total time is the average speed.
An object may not move at the same speed throughout; sometimes it may move slower or faster.
In this context, the term speed is used to mean average speed.
Science and Society: Measuring Speed and Distance in Vehicles
Vehicles like scooters, motorbikes, cars, and buses have an instrument called a speedometer.
A speedometer shows the vehicle’s speed in kilometres per hour (km/h).
Another instrument called an odometer measures the total distance travelled by the vehicle in kilometres.
Uniform and Non-uniform Linear Motion
Linear Motion
When an object moves along a straight line, the motion is called linear motion.
Example: A train moving on a straight track between two stations.
This motion can be uniform (at a constant speed) or non-uniform (with changing speed).
Uniform Linear Motion
When an object moves along a straight line with a constant (unchanging) speed.
It covers equal distances in equal intervals of time.
Example: Car moving from one point to another at constant speed.
Non-Uniform Linear Motion
When the speed of an object keeps changing while moving along a straight line.
It covers unequal distances in equal intervals of time.
Example: Car moving from A to B and C to D with changing speeds.
Real-life Note: Uniform motion is an ideal concept. In real life, objects rarely move at a constant speed for long durations — hence, we use average speed.
Case Study : In Table , data are given for the distances travelled by two trains, X and Y, between the time 10:00 AM and 11:00 AM.
Which of the two trains is in uniform linear motion between 10:00 AM and 11:00 AM?
Solution : Train X covers equal distances in equal intervals of time, so it is in uniform linear motion while Train Y is in non-uniform linear motion.
Answer:
Train X is in uniform linear motion between 10:00 AM and 11:00 AM because it covers equal distances (20 km) in equal time intervals (10 minutes).
Train Y, on the other hand, is in non-uniform linear motion because the distances it covers in each 10-minute interval are not equal (e.g., 20 km in the first interval, 15 km in the second, and so on).
Thus, Train X moves uniformly, while Train Y does not.
Terms to Remember
Sundial: A device that uses the Sun’s shadow to show the time of day.
Water Clock: A device that measures time by the flow of water in or out of a vessel.
Hourglass: A device that measures time by the flow of sand between two bulbs.
Candle Clock: A candle with markings that shows time as it burns.
Pendulum: A weight (bob) hanging from a fixed point that swings back and forth to measure time.
Time Period: The time taken for one complete oscillation of a pendulum.
Second: The SI unit of time, symbolized as “s.”
Speed: The distance covered by an object in a unit of time, measured in m/s or km/h.
Speedometer: An instrument in vehicles that shows speed in km/h.
Odometer: An instrument in vehicles that measures distance traveled in km.
Linear Motion: Motion along a straight line.
Uniform Linear Motion: Motion along a straight line at a constant speed, covering equal distances in equal times.
Non-uniform Linear Motion: Motion along a straight line with changing speed, covering unequal distances in equal times.
Average Speed: The total distance covered divided by the total time taken, used when speed varies.
Ghatika-yantra: A sinking bowl water clock used in ancient India to measure time in ghatis.
Ghati: A time unit of 24 minutes, measured by the Ghatika-yantra.
Pema and her brother Palden live in Gangtok. One cold winter evening, they sit near a fireplace. Palden talks about his trip to Kerala during winter. He says Kerala is warmer and more humid than Gangtok.
Their grandfather explains, “Kerala is closer to the equator and has a long coastline, so it is warmer and more humid.” Palden adds, “We learned that the Sun is the main source of heat and light, and places near the equator are usually hot.”
While they talk, Pema watches her grandmother cooking thukpa (a traditional Sikkimese dish) in a big metal pan. She asks, “Why are cooking utensils usually made of metal?” Palden answers, “Because metals are good conductors of heat,” which they studied in their science chapter.
Let’s dive into nature of heat and its transfer in nature!
Conduction of Heat
Conduction is the process by which heat is transferred from the hotter part of an object to its colder part through direct contact. In solids, especially metals, particles vibrate when heated and pass this energy to neighboring particles without moving from their positions. This makes conduction an important process in everyday activities like cooking.
How Conduction Works: When one end of a metal object is heated, the particles at that end gain energy and vibrate more. These vibrations are passed to adjacent particles, transferring heat along the object. For example, when a metal pan is heated, the heat travels from the flame to the entire pan, making it hot.
Let us perform an activity to learn why certain materials are good conductors of heat.
Materials Needed: Metal strip (aluminium or iron), Four pins, Candle or spirit lamp, Stand (or two bricks for support), Wax to attach the pins, Heat source
Steps:
Take a metal strip (15 cm long) and attach four pins to it using wax, spaced about 2 cm apart.
Secure the strip to a stand or between two bricks.
Heat the end of the strip away from the stand with a candle or spirit lamp.
Observe and predict the behaviour of the pins.
Heat transfer in a metal strip
Prediction: You are asked to predict the order in which the pins will fall as the strip is heated.
Observation: The first pin (Pin I), closest to the candle flame, falls first, followed by the other pins in order (II, III, and IV). The reason for the sequential fall of the pins is the process of heat conduction.
Conclusion
Conduction is the process of heat transfer from the hotter part of a material to the cooler part. As the heat travels along the metal strip, it causes the wax holding each pin to melt, leading to the pin falling.
The heat is transferred from the hot end (near the flame) to the colder end through the metal particles vibrating and passing on the energy to their neighbours.
Metals are good conductors of heat, which is why metal utensils are used for cooking.
Conductors and Insulators of Heat
1. Good Conductors of Heat:
Metals (e.g., aluminium, iron) allow heat to pass through them easily.
This is why metal cooking utensils are commonly used.
2. Poor Conductors of Heat (Insulators):
Materials like wood, glass, clay, and porcelain do not allow heat to pass through easily. For example:
Tea or coffee cups made of clay or porcelain help in retaining heat longer.
Woollen fabrics trap air, which is a poor conductor, and help keep us warm.
The presence of air between layers of clothing (such as woolen clothes or blankets) reduces heat flow and helps keep us warm.
Air trapped between two thin blankets acts as an insulator
How Air Acts as an Insulator and Its Applications in Daily Life
1. Woollen Fabric and Heat Retention
Woollen fabric traps air in its tiny pores or gaps.
Since air is a poor conductor of heat, it reduces the flow of heat from our bodies to the cooler surroundings.
This trapped air acts as insulation, helping to keep us warm in cold weather.
Similarly, when multiple layers of clothing trap air between them, the air acts as an insulator and keeps the body warm.
2. Blankets and Trapped Air
The presence of air between two thin blankets makes them warmer compared to a single thick blanket.
This is because the air layer between blankets slows down heat loss from our body, making us feel warm and cozy.
3. Insulated Houses: Using Heat Transfer Principles
Is it possible to build houses that remain comfortable inside despite very hot or cold outside weather?
Yes, houses in extreme climates use the concept of heat transfer to stay warm in winter and cool in summer.
4. Hollow Bricks and Heat Insulation
Some houses use hollow bricks for their outer walls.
Air trapped inside the hollow parts of these bricks acts as a poor conductor of heat.
This trapped air helps keep the house warm in winters by reducing heat loss and cool in summers by reducing heat gain.
Thus, hollow bricks help maintain a comfortable indoor temperature by slowing heat transfer through the walls.
Fascinating Facts
The upper regions of the Himalayas, such as the Mori block of Uttarkashi in Uttarakhand, experience extremely cold climates and heavy snowfall in winters.
To keep houses warm in such harsh conditions, people build walls with two wooden layers.
The space between these wooden layers is filled with cow dung and mud.
Both wood and mud are poor conductors of heat, meaning they do not allow heat to escape easily.
This natural insulation prevents heat loss, helping keep the houses warm and cozy during winter.
Try yourself:
What is conduction?
A.Heat transfer through liquids
B.Heat transfer through direct contact
C.Heat transfer through air
D.Heat transfer through radiation
View Solution
Convection
Convection is the process of heat transfer in liquids and gases, where heated particles move and carry heat with them. This movement creates currents, such as breezes near the sea or the rising of smoke, making convection a key process in nature.
How Convection Works?
When a liquid or gas is heated, its particles gain energy, become less dense, and rise.
Cooler, denser particles then move to take their place, creating a cycle of movement called a convection current.
For example, when water is heated in a pan, the warmer water rises, and cooler water sinks, distributing heat.
Convection in Gases: In air, heated air expands, becomes lighter, and rises.
For example: Smoke rises because it is made up of hot gases and tiny solid particles that are released when something burns.
When these particles are heated, they become lighter than the surrounding air, causing them to rise.
This is similar to what happens when air is heated; it expands, takes up more space, and becomes less dense, which is why warm air also rises.
Convection in Liquids: In liquids like water, heated particles rise, and cooler ones sink, creating a circular flow.
To understand why smoke rises more clearly, let us perform an activity.
Materials Needed: paper cups, a wooden stick, threads, a burning candle.
Procedure:
Hang the paper cups in an inverted position on the wooden stick using threads.
Place the stick horizontally.
Light a candle and place it under one of the cups.
Observe what happens to the cups.
Observations and Explanation:
The cup with the candle underneath it rises because the air inside the cup heats up.
When air is heated, it expands and takes up more space, making it lighter. This causes the cup to rise.
Hot air rising up
Example of Air Expansion:
When a partially inflated balloon is placed in the Sun, the air inside it heats up and expands, causing the balloon to become larger.
Smoke Rising:
When an incense stick is burnt, the smoke produced is a mixture of hot gases and tiny solid particles.
Since the smoke is warmer than the surrounding air, it rises.
Convection in Liquids:
To understand how heat transfer occurs in liquids, we can perform an activity.
Materials Needed: 500 mL beaker, water, straw, potassium permanganate, candle.
Procedure:
Fill the beaker halfway with water.
Using a straw, place a grain of potassium permanganate at the center of the beaker’s base.
Place a candle under the center of the beaker’s base.
Observe the movement of the colored streak in the water.
Observations:
As heat is supplied, a streak of color starts moving up from the center and coming down from the sides of the beaker.
Demonstration of convection in heated water
Explanation:
The water at the bottom of the beaker gets heated, becomes lighter due to expansion, and rises.
The cooler, heavier water from the sides then comes down to take its place.
This creates a continuous cycle until the entire volume of water is heated.
Conclusion:
The movement of the colored streak in the water demonstrates convection, which is how heat transfer occurs in liquids and gases through the movement of particles.
Just like air, water gets heated through convection, where particles move from one place to another, carrying heat with them.
Land and Sea Breeze
During the day, the land near the beach heats up faster than the water in the sea. This is because different materials absorb heat at different rates.
However, at night, the situation changes: the land cools down faster than the water.
This difference in how quickly land and water heat up and cool down is what causes the land and sea breeze.
Let us check how land and water get heated and cooled by performing an activity.
Materials Required: Two identical bowls, Soil , Water and Two laboratory thermometers
Procedure:
On a clear, sunny day, under the supervision of a teacher or an adult, take two identical bowls.
Fill one bowl halfway with soil and the other bowl halfway with water.
Fix a laboratory thermometer in each bowl, ensuring that the bulbs are immersed in the soil and water, respectively, and do not touch the bottoms or sides of the bowls.
Place the set-up in sunlight.
Observe the rise in temperature of the soil and water over a period of time.
Observations:
After 20 minutes, you will find that the temperature of the soil rises more than that of the water. This indicates that the soil heats up faster than water.
Cooling Experiment:
After letting the soil and water heat up, bring the set-up indoors and allow it to cool for 20 minutes.
Observe the cooling rates of the soil and water.
Conclusion:
Soil heats up faster than water.
Soil also cools faster than water.
Sea Breeze
During the day, when the land heats up quickly, the air above the land also becomes warm and rises.
This creates a low-pressure area over the land.
Meanwhile, the air above the sea is cooler and denser.
To fill the low-pressure area over the land, the cooler air from the sea moves in, creating a sea breeze.
This is why people living in coastal areas feel a refreshing breeze coming from the sea during the day.
Sea Breeze
Land Breeze
At night, the land cools down faster than the sea.
The air above the land becomes cooler and denser, creating a high-pressure area.
Meanwhile, the air above the sea is still relatively warm and rises, creating a low-pressure area.
To balance the pressure, the cooler air from the land moves towards the sea, creating a land breeze.
This is why people living near the shore experience a change in wind direction from day to night.
Land Breeze
Try yourself:
What happens to air when it is heated?
A.It becomes less dense and rises.
B.It becomes denser and sinks.
C.It cools down immediately.
D.It remains the same.
View Solution
Radiation
Radiation is heat transfer do not need any medium. All objects emit heat this way.
Heat transfer happens directly from the a hot object to us through a process called radiation.
For example, the Sun’s heat reaches Earth by radiation. The Sun’s hot surface (about 6000°C) emits energy waves, some of which warm the Earth.
Radiation does not require a medium, which is why we can feel the warmth of the Sun even though space is a vacuum.
Examples of Heat Transfer in Daily Life ( Combining all the three Processes)
Many everyday examples show conduction, convection, and radiation happening at the same time. For example, when water is heated in a pan:
Heat moves from the flame to the pan by conduction.
Water inside the pan heats up by convection.
The warmth we feel around the flame and pan is due to radiation.
Fascinating Facts: The Himalayan Bukhari
In the upper Himalayan region, a traditional room heater called bukhari is used to keep rooms warm in winter. It is an iron stove where wood or charcoal is burned. A long pipe attached at the top acts as a chimney to release smoke. The flat top of the bukhari can also be used for cooking by placing utensils on it.
When the bukhari is used, all three types of heat transfer—conduction, convection, and radiation—work together to warm the room and cook food.
Water Cycle
Water exists in three states in nature
Liquid: in oceans, rivers, lakes
Solid: as snow, glaciers, ice sheets in mountains and polar regions
Gas: as water vapor in the atmosphere
During summer, snow and ice melt due to the Sun’s radiation, forming rivers that flow into oceans. Fresh snow replenishes the ice in winter.
Water in oceans, rivers, and lakes evaporates due to the Sun’s heat. Plants also release water vapor through transpiration.
Water vapor rises, cools, and condenses to form clouds. Clouds cause precipitation (rain, snow, hail).
This continuous movement of water—evaporation, condensation, precipitation, infiltration, and runoff—is called the water cycleWater cycle
Importance of Water Cycle
The water cycle is the process through which water continuously moves upward as water vapor and downward through precipitation, passing through soil, rocks, and plants before returning to water bodies. This cycle helps to redistribute and replenish water in rivers, lakes, and oceans while conserving the total amount of water on Earth.
Know a Scientist: Varahamihira
Varahamihira was a famous astronomer and mathematician of the 6th century CE from Ujjaini (now Ujjain), Madhya Pradesh. In his work Brihatsamhita, he described methods to predict seasonal rainfall. His predictions were based on observations of cloud formation, wind patterns, the positions of stars and the moon, and other natural phenomena.
Seepage of Water Beneath the Earth’s Surface
Let’s Fisrt Perform Activity to understand : How does water seep through the surface of the Earth?
Take three transparent, used plastic bottles of 1 L capacity.
Cut them in the middle and make a small hole in the cap of each bottle.
Keep them inverted and put some clay in one bottle, sand in the second, and gravel in the third.
Place three identical beakers below each bottle.
Add 200 mL of water to each bottle.
Predict the amount of water flowing out of each bottle.
Collect the water that flows through each bottle for 10 minutes.
Compare the amount of water that comes through each bottle.
An activity to compare the flow of water through clay, sand and gravel
You may have observed that water flows fastest through gravel, slower through sand, and slowest through clay. This is due to the differences in the particle sizes and the spaces between them:
Gravel: The spaces between gravel particles are wider, allowing water to pass through quickly.
Sand: The particles are smaller than gravel, so the spaces are narrower, causing slower water flow.
Clay: The smallest particles create very tight spaces, restricting water flow the most.
Now let’s learn the theory and definition
When rainwater or surface water seeps down through the soil and rocks beneath the Earth’s surface, this process is called infiltration.
The ease with which water infiltrates depends on the size and connectivity of the spaces between soil and rock particles. If these spaces (called pores) are wider, open, and well connected, water seeps through more quickly and easily.
Once water infiltrates, it moves down and gets stored in the tiny spaces or pores within sediments (loose soil, sand, gravel) and the cracks or openings in rocks below the surface. This stored water is known as groundwater.
The underground layers of sediments and rocks that hold this water are called aquifers.
We access groundwater by digging wells or drilling bore wells into these aquifers.
The depth of groundwater can vary greatly — it might be just a few meters below the surface or hundreds of meters deep, depending on the region.
Although groundwater is a vital source of water, it is not unlimited.
Increasing population and their growing water needs have caused excessive extraction of groundwater.
Urbanization has reduced the natural areas where water can seep into the ground:
Less vegetation cover means fewer plants and trees to help water infiltrate.
More concrete surfaces (roads, buildings) prevent water from soaking into the soil.
Due to these factors, the rate of groundwater recharge is reduced, leading to groundwater depletion.
To conserve and replenish groundwater, techniques like:
Rainwater harvesting — collecting and storing rainwater for later use.
Recharge pits — specially made pits that help rainwater seep into the ground.
These methods help recharge groundwater, supporting the natural water cycle and ensuring a sustainable supply of groundwater for future needs.
Water scarcity makes life hard, so people find ways to save water.
In Ladakh, they make ice stupas—artificial ice cones built in winter.
These ice stupas melt slowly in warmer months, providing water for farming and daily use.
Science and Society: Ice Stupa
In Ladakh, spring streams often dry up because the sun’s heat is not enough to melt mountain snow quickly.
During winter, water from mountain streams is sent through underground pipes and sprayed into the cold air.
The water freezes layer by layer, forming a tall, cone-shaped ice structure called an ice stupa.
The ice stupa melts slowly in spring, supplying water for farming and other needs throughout summer.Ice Stupa
Try yourself:
What process does the water cycle involve for returning water to the Earth’s surface?
A.Evaporation
B.Infiltration
C.Transpiration
D.Condensation
View Solution
Terms to Remember
Conduction: The process of heat transfer through direct contact, where particles pass heat to neighboring particles without moving.
Convection: The transfer of heat in liquids and gases by the movement of heated, less dense particles.
Radiation: The transfer of heat through waves, without needing a medium, as seen in heat from the Sun or a fire.
Insulator: A material (e.g., wood, glass) that does not allow heat to pass through easily, also called a poor conductor.
Evaporation: The process where water turns into vapor due to heat, especially from the Sun.
Condensation: The cooling of water vapor to form liquid droplets, creating clouds.
Precipitation: The release of water from clouds as rain, snow, or hail.
Transpiration: The release of water vapor by plants into the atmosphere.
Aquifer: Underground layers of rock or soil that store groundwater.
Seepage: The process by which water moves through soil or rock into the ground.
Bukhari: A traditional Himalayan heater that uses wood or charcoal to warm rooms and cook food.
Ice Stupa: A cone-shaped ice structure in Ladakh that stores water in winter and releases it in spring.
Summary
Heat transfer occurs through three processes: conduction, convection, and radiation. Conduction involves heat moving through solids, like metals, by particle vibrations, making metals ideal for cooking utensils. Convection occurs in liquids and gases, where heated particles move, creating currents like sea and land breezes. Radiation transfers heat without a medium, as seen in the Sun’s heat or warmth from a fire. The water cycle, driven by the Sun’s heat, involves evaporation, condensation, precipitation, and seepage, redistributing and conserving Earth’s water. Groundwater is replenished through seepage, but conservation methods like ice stupas and rainwater harvesting are vital to address scarcity.
The life of a plant starts from a tiny seed. With proper care, it grows into a sapling and then a mature plant, which can produce flowers, fruits, and new seeds. But it takes time for a plant to grow before it can make seeds again.
Similarly, animals and humans also grow and change before they can reproduce. Some animals lay eggs, while others give birth to young ones. These young ones grow slowly and develop over time.
In humans, life moves through different stages: infancy, childhood, adolescence, adulthood, and old age. Between ages 10 to 19, we go through adolescence, a time of fast physical, emotional, and mental growth. During this stage, the body begins to prepare for adulthood and reproduction.
Let’s explore the changes that happen during adolescence and learn how to handle them responsibly.
Growing with Age: The Teenage Years
What is Adolescence?
Adolescence is the transitional stage between childhood and adulthood, starting around age 10 and lasting until age 19, characterized by rapid physical and other changes.
Changes During Adolescence
As children grow into teenagers, their bodies and minds go through many physical and emotional changes. These changes are natural and happen at different times for different people.
Here are some common changes:
1. Increase in Height and Body Shape
Boys and girls grow taller quickly.
Boys may gain weight, have broader shoulders, and wider chests.
Girls may notice breast development and body shape changes.
2. Change in Voice
Boys’ voices become deeper due to the growing voice box (also called the Adam’s apple).
Girls may also experience slight changes in their voice.
3. Hair Growth
Hair begins to grow in the armpits and pubic area in both boys and girls.
Boys also develop facial hair like a moustache or beard, and sometimes chest or back hair.
The amount and timing of hair growth vary from person to person.
4. Changes in Skin
Many teens get pimples or acne because of oily skin during this time.
Acne is common and happens when oil blocks skin pores.
A Key Point to Remember
Everyone goes through these changes at their own pace.
Some may grow faster or slower, and that’s completely normal.
These changes are part of growing up.
Secondary Sexual Characteristics
Certain changes, like voice deepening in boys, facial and chest hair growth in boys, and breast development in girls, are called secondary sexual characteristics.
These characteristics distinguish males from females but are not directly involved in reproduction.
They signal the onset of puberty, the stage where the body prepares for adulthood and reproductive capability.
What is Puberty?
Puberty is the stage when both external and internal changes prepare the body for reproduction. It marks the beginning of adolescence and the path toward becoming an adult.
Try yourself:
What is the age range for adolescence?
A.10 to 19 years
B.5 to 10 years
C.20 to 25 years
D.1 to 5 years
View Solution
Changes that Indicate Reproductive Capability
Adolescence brings not just visible changes like height or voice, but also important internal changes — especially those related to reproduction.
Menstrual Cycle in Girls:
The menstrual cycle, commonly called “the period,” is a natural process in adolescent girls, marking reproductive maturity.
It usually occurs every 28–30 days, but it can vary between 21–35 days.
The time when blood comes out from the body is called menstruation and it lasts for 3 to 7 days.
Some girls may feel pain or discomfort in the lower belly during this time.
Menstruation is a normal and healthy sign of reproductive growth.
It naturally stops between the ages of 45–55, marking the end of a woman’s ability to reproduce.
Menstrual Cycle
Breaking Myths About Menstruation
In many places, there are wrong beliefs and taboos about periods.
Some believe girls should stay isolated during menstruation — this is not correct.
Menstruation is natural and healthy, and there’s no need for shame or fear.
Understanding it with a scientific outlook helps support women’s health and removes unnecessary taboos.
Emotional and Behavioral Changes in Adolescents
Adolescence is not only a time of physical growth — it’s also a time of strong emotions and changes in behaviour. These changes can feel exciting, confusing, or even overwhelming, but they are a normal part of growing up.
Let’s understand some common emotional changes and how they affect behaviour — along with ways to handle them positively.
Emotional Changes, Behaviour, and Positive Growth
Understanding and Managing Emotions
Adolescents often feel emotions more strongly than children.
These emotions can lead to new interests, such as helping others or exploring creative hobbies.
By understanding your feelings, you can make thoughtful choices and respond to situations in a healthy and balanced way.
Try yourself:
What is the typical duration of menstruation?
A.3–7 days
B.1–2 days
C.10–14 days
D.5–10 days
View Solution
Making Adolescence a Joyful Experience
Adolescence is a special journey filled with curiosity, energy, and new experiences. To make this stage happy and healthy, it’s important to take care of your body and mind. Good habits, smart choices, and staying positive can make a big difference!
Meeting Nutritional Needs
Adolescence requires a nutritious diet to support rapid growth and development.
Nutrients Needed
Proteins and Carbohydrates: Essential for growth, strength, and energy, found in foods like milk, millets, and curd.
Calcium: Supports bone growth, found in milk, cheese, and paneer.
Iron: Aids blood formation, found in spinach, kidney beans, and dried fruits like raisins.
Fats, Vitamins, Minerals: Needed in adequate amounts for overall health.
Health Concerns: Adolescents, especially girls, may face blood-related issues due to iron or vitamin B12 deficiency, which can be managed with a balanced diet.
Science and Society: Iron Deficiency in Adolescents
Many adolescents, especially girls, may suffer from iron deficiency. This can lead to tiredness, weakness, or even anaemia (a blood-related health problem).
To prevent this:
Eat iron-rich foods like spinach, jaggery, lentils, and dried fruits
Include vitamin C (like oranges or amla) with iron-rich foods to help absorb iron better
Government programs like Iron and Folic Acid (IFA) supplementation provide free tablets in many schools
Know a Scientist: Dorothy Hodgkin
Dorothy Hodgkin was a great chemist who studied vitamin B12, which is needed for a healthy body and blood.
She won the Nobel Prize in Chemistry in 1964.
Our body can’t make vitamin B12, so we must get it from food like dairy, eggs, and meat. Talk to your teacher or family to know more about foods rich in B12!
Personal Hygiene
Along with eating healthy food, personal hygiene is essential during adolescence.
During this stage, your body goes through many changes.
Keeping your body clean, especially in the armpits and pubic area, helps prevent infections.
Menstrual Hygiene for Girls
Girls must take extra care of hygiene during menstruation (periods).
Use sanitary pads or reusable cloth pads to stay clean and comfortable.
Dispose of used pads properly: wrap them in newspaper and throw them in a covered dustbin.
Today, biodegradable sanitary pads are also available, which are safe for the environment.
Breaking the Stigma
Menstruation is natural, and there is no need for shame. Society must:
Provide clean toilets and safe spaces in schools and public places.
Help make sanitary products easily available.
Talk openly about menstrual hygiene to support girls and women.
Science and Society: Government Support for Menstrual Hygiene
Physical Activities
Benefits: Regular exercise, games, and sports keep the body and mind fit, build stamina, and boost mood.
Examples: Activities like running, cycling, or team sports promote overall health.
Importance: Physical activity supports growth, reduces stress, and enhances well-being during adolescence.
Balanced Social Life
We all live together in society and interact with many people every day. Being polite and respectful helps create a friendly and safe environment for everyone.
Adolescence and Social Interaction
Adolescence brings new feelings and experiences.
Teens may feel attracted to their friends and often copy their behavior.
Many now interact online through social media and messaging apps.
Using Technology Responsibly
Technology lets us connect, learn, and share information easily.
It’s important to use social media carefully and responsibly.
Sometimes, people may use social media carelessly or hurt others without meaning to.
If you face cyberbullying (mean messages, rumors, sharing private info), don’t be scared — tell your parents or teachers right away.
Dos and don’ts to be followed on social media
Science and Society: Cyberbullying
Cyberbullying means using phones or computers to hurt others by sending mean messages or sharing private info without permission. It is important to stay safe and seek help if you face it.
Avoiding Harmful Substances
During adolescence, some people may try to pressure you to use harmful substances like tobacco, cigarettes, alcohol, or illegal drugs. Because of curiosity and excitement, teens might be tempted to try them.
Why Avoid These Substances?
They are harmful to your body and mind.
They are addictive, meaning once you start, you might want to keep using them again and again.
This addiction is called substance abuse.
Using these substances can cause serious health problems like lung damage, breathing difficulties, and memory loss.
Condition of the lungs before and after prolonged exposure to bidi/cigarette smoke
Be Strong and Say NO!
Say NO the very first time and every time someone offers these substances.
Remember, people who are addicted often started with just one try.
Choose healthy habits instead.
If you or someone you know is struggling, talk to trusted adults like parents or teachers for support.
Counselling and medical help are available and important.
Science and Society: Nasha Mukt Bharat Abhiyaan
This is a government campaign to raise awareness about avoiding substance abuse.
It focuses on preventing addiction, especially among children and youth.
A National De-addiction Helpline (14446) is available for help with drug addiction.
Try yourself:
What is essential for growth, strength, and energy during adolescence?
A.Vitamins
B.Proteins and Carbohydrates
C.Fats
D.Minerals
View Solution
The ‘Why’ Question for Adolescence
Adolescence involves many physical and emotional changes.
These changes occur mainly due to hormones, which are chemical messengers produced in the body.
Hormones regulate growth, development, and various body functions.
They are released at specific times based on signals from the brain.
Some hormones also influence mood and behavior during adolescence.
Understanding these changes, seeking guidance when needed, and making healthy choices help build a strong foundation for life.
Points to Remember
Adolescence is the stage from about 10 to 19 years when a child grows into an adult.
Physical changes include getting taller, gaining weight, and developing features like facial hair in boys and breasts in girls.
Puberty prepares the body for having babies, and girls start their menstrual cycle (period) every 3–4 weeks.
Menstruation is natural, and using sanitary pads helps keep girls healthy. Myths about periods are not true.
Teenagers may have mood swings and feel more sensitive, but these feelings can lead to creativity and kindness.
Eating healthy foods with protein, calcium, and iron helps growth. Lack of iron or vitamin B12 can cause health problems.
Good hygiene, especially during periods, is important to avoid infections. Governments provide help with sanitary pads.
Exercise and sports keep the body strong and the mind happy.
Use social media carefully and ask adults for help if you face problems like cyberbullying.
Avoid harmful substances like tobacco, alcohol, and drugs because they harm health and cause addiction.
Hormones cause many changes in the body and feelings during adolescence.
Learning about these changes and making good choices helps you grow up healthy and strong.
Difficult Words and Their Meanings
Adolescence: The stage of life between childhood and adulthood (ages 10–19), marked by rapid physical, emotional, and behavioral changes.
Puberty: The phase during adolescence when the body develops into an adult capable of reproduction, involving external and internal changes.
Secondary Sexual Characteristics: Physical traits (e.g., facial hair in boys, breast development in girls) that distinguish males from females but are not directly involved in reproduction.
Menstrual Cycle: A natural process in girls where blood is discharged (menstruation) every 28–30 days, signaling reproductive health.
Menstruation: The phase of the menstrual cycle involving blood discharge, lasting 3–7 days, typically starting at puberty and ending by ages 45–55.
Hormones: Chemicals produced in the body that regulate growth, development, mood, and functions like menstruation or puberty.
Mood Swings: Sudden changes in emotions, common in adolescents, like feeling happy one moment and low the next.
Personal Hygiene: Practices like keeping the body clean to prevent infections, especially important during adolescence.
Menstrual Hygiene: Using sanitary pads or cloth pads during menstruation to stay clean and healthy, with proper disposal to protect the environment.
Cyberbullying: Harassing others online through messages, rumors, or sharing private information, which adolescents should handle by seeking help.
Substance Abuse: Regular use of harmful, addictive substances like tobacco, alcohol, or drugs, causing health issues like lung damage or memory loss.
Addiction: A strong urge to repeatedly use harmful substances, making it hard to stop after starting.
We see many changes happening all around us every day. Ice melts into water, flowers bloom from buds, fruits change color and smell, and cold water becomes warm over time. These changes can affect how things look, smell, feel, or taste. Using our five senses — sight, smell, touch, hearing, and taste — we can observe and understand these changes better.
Let’s explore some common changes around us and learn how to notice them carefully.
A Substance May Change in Appearance but Remain the Same
What is a Physical Change?
A physical change is when a substance or object changes in appearance (e.g., shape, size, state) but remains the same substance, with no new material formed.
Physical Changes
Key Features
Only physical properties like shape, size, or state change.
The substance’s chemical composition remains unchanged.
Examples include melting ice, boiling water, or folding clothes.
Examples
Paper Folding: Folding paper into shapes (e.g., a boat or plane) changes its form, but unfolding it returns the original paper.
Balloon Inflation: Inflating a balloon stretches it, but letting the air out returns it to its original shape. However, pricking an inflated balloon causes it to burst, and the original shape cannot be restored, though the rubber material remains the same.
Crushing Chalk: Crushing chalk into powder changes its form, but the material (chalk) stays the same, though the original piece cannot be reformed.
Water’s States: Water changing from solid (ice) to liquid (water) to gas (steam) is a physical change, as it remains water despite changing states.
Try yourself:
What is a physical change?
A.A change that creates a new substance.
B.A change in appearance without new material.
C.A change that cannot be undone.
D.A change that occurs only in nature.
View Solution
A Substance May Change in Appearance and Not Remain the Same
What is a Chemical Change?
When substances react chemically, they form new substances with different properties. This is called a chemical change. Unlike physical changes where only appearance or state changes, chemical changes create entirely new materials.
Chemical Changes
Examples:
1. Blowing Air into Lime Water
A common example is when carbon dioxide (CO₂) gas comes into contact with lime water (a solution of calcium hydroxide). Lime Water Turns Milky
The carbon dioxide reacts with the lime water to form calcium carbonate, which is a white solid that makes the solution look milky or cloudy.
This solid eventually settles at the bottom of the container.
Along with calcium carbonate, water is also formed during this reaction.
This reaction can be written as: Calcium hydroxide + Carbon dioxide → Calcium carbonate + Water
This shows that a new substance, calcium carbonate, is produced, proving that a chemical change has taken place.
2. Vinegar and Baking Soda
Another example is the reaction between vinegar (which contains acetic acid) and baking soda (sodium bicarbonate).
When these two substances mix, they react to produce carbon dioxide gas, which can be seen as bubbling or fizzing.
This gas, when passed through lime water, turns the lime water milky due to the formation of calcium carbonate.
This confirms that carbon dioxide gas was produced by the chemical reaction.
Try yourself:
What happens to lime water when carbon dioxide is blown into it?
A.It evaporates.
B.It turns milky.
C.It remains unchanged.
D.It becomes fizzy.
View Solution
Some Other Processes Involving Chemical Changes
Rusting
Rusting is a chemical change where iron reacts with air and moisture to form a new substance called rust (iron oxide).
This brown-colored substance forms on iron objects like nails and makes them weak and crumbly.
Since a new substance is formed, rusting is a chemical change.
Rusting of Iron
Combustion
Combustion is a chemical reaction where a substance reacts with oxygen, producing heat and/or light. Substances that burn are called combustible substances (e.g., wood, paper, cotton, kerosene).
An example is burning magnesium ribbon. When magnesium burns in air, it forms magnesium oxide, a white powder, and releases heat and light.
This shows that combustion involves forming new substances along with energy release.
The chemical reaction for burning magnesium can be written as: Magnesium + Oxygen → Magnesium oxide + Heat + Light (Ribbon) (Air) (White powder)
Substances that can catch fire and burn are called combustible substances. Examples include wood, paper, cotton, and kerosene.
Oxygen’s Role in Combustion
Oxygen from the air is essential for combustion.
If you cover a burning candle so it cannot get air, the flame goes out because there is no oxygen to support burning.Candle (a) burning (b) covered with a glass tumbler
During combustion, carbon in the fuel reacts with oxygen to form carbon dioxide gas.
Carbon dioxide can be detected by passing it through lime water, which turns milky due to the formation of calcium carbonate.
This confirms that oxygen supports burning and that combustion produces carbon dioxide.
What Else is Needed to Start Combustion?
Besides fuel (the combustible substance) and oxygen, heat is required to start combustion. This heat raises the fuel’s temperature to a point called the ignition temperature, at which it catches fire.
For example, paper will catch fire quickly if touched with a lighted matchstick because the matchstick’s temperature is above paper’s ignition temperature.
However, paper can also catch fire without a matchstick if focused sunlight heats it enough. Using a magnifying glass to concentrate sunlight on paper can increase its temperature until it starts burning.Paper catching fire
Three Requirements for Combustion
To start and maintain combustion, these three things are necessary:
Fuel (Combustible substance) — Something that can burn.
Oxygen — To support the burning process.
Heat — To raise the fuel to its ignition temperature.
Fire Triangle: Combustion requires fuel, oxygen, and heat (ignition temperature), represented as a triangle.Fire triangle
Fascinating Fact
Have you seen tiny glowing insects in gardens at night?They are called fireflies, and their light comes from a chemical change inside their bodies. This special kind of light, made without heat, is called bioluminescence.
Science and Society
What to do if someone’s clothes catch fire? Wrap them in a blanket or cloth to stop the air supply — this helps put out the fire.
Important: Never use synthetic blankets or clothes, as they can melt and stick to the skin, causing more harm.
Try yourself:
What substance is formed when iron rusts?
A.Water
B.Iron oxide
C.Carbon dioxide
D.Magnesium oxide
View Solution
Can Physical and Chemical Changes Occur in the Same Process?
Burning a Candle Physical Changes
Melting Wax: Heat from the flame melts solid wax into liquid, a physical change as no new substance forms.
Evaporation: Liquid wax moves up the wick and evaporates into vapor, another physical change.
Solidification: Wax dripping and cooling back into solid is also physical.
Burning a Candle Chemical Change:
Burning Wax Vapor: The wax vapor burns in the presence of oxygen, producing carbon dioxide, water, heat, and light, forming new substances, indicating a chemical change.
Conclusion
Burning a candle involves both physical changes (melting, evaporation) and a chemical change (burning), showing that some processes combine both types.
Know A Scientist: Michael Faraday
Scientist Michael Faraday studied candles in the 19th century, using them to explain physical and chemical processes like melting, vaporization, and combustion in his lectures, “Chemical History of a Candle.”
Are Changes Permanent?
Reversible Changes
Definition: Changes where the original substance or object can be restored.
Examples:
Melting Ice: Ice melts into water, but freezing the water reforms ice.
Boiling Water: Water turns to steam, but condensing the steam returns liquid water.
Folding Paper: Folding and unfolding paper restores its original shape.
Irreversible Changes
Definition: Changes where the original substance or object cannot be restored.
Examples:
Chopping Vegetables: Cut pieces cannot be reassembled into the whole vegetable.
Making Popcorn: Corn kernels transform into popcorn, which cannot revert to kernels.
Burning Wood: Wood turns to ash, which cannot become wood again.
Are All Changes Desirable?
Desirable Changes
Changes that are useful or beneficial.
Examples:
Milk to Curd: Curdling produces tasty curd.
Ripening Fruits: Fruits become sweet and edible.
Cooking Food: Raw ingredients become nutritious meals.
Cutting Fruits: Makes them easier to eat.
Undesirable Changes
Changes that are harmful or unwanted.
Examples:
Rusting of Iron: Damages tools and structures.
Food Decay: Spoils stored food, making it inedible.
Some changes can be good or bad depending on the situation
Decomposing food is bad if it rots in the kitchen, but good when it’s used to make compost for plants.
Environmental Impact
Human activities, like burning fuels in vehicles or drying paint, release carbon dioxide and pollutants, increasing atmospheric pollution over time.
These changes have long-term effects on the environment, like climate change.
Try yourself:
What happens to wax when it is melted by a candle flame?
A.It forms a new substance.
B.It evaporates into vapor.
C.It becomes liquid without a new substance.
D.It turns into ash.
View SolutionSome Slow Natural Changes Weathering of Rocks
Weathering is the process where rocks break down into smaller pieces (sediments) through physical and chemical changes, eventually forming soil.
1. Physical Weathering
Caused by temperature changes, tree roots growing into cracks, or water freezing in rock crevices, breaking rocks into smaller pieces.
Example: Sediments like sand, soil, and stones collect at the base of mountains or cliffs.
2. Chemical Weathering:
Occurs when water or chemicals in water react with rock components.
Example: Basalt rock, containing iron, reacts with water or air to form a red layer of iron oxide (similar to rust), changing its composition.
Together, these changes help break down rocks and form soil, which is important for plant growth and life on Earth.
Erosion
Erosion is the physical process where rocks, soil, and sediments are broken down and moved by natural forces like wind or flowing water.
Examples
You may have seen fine sand on riverbeds or lakes—this is created when larger rocks and soil are worn down and moved by rivers or wind.
River rocks become smooth over time because the flowing water keeps rubbing them, slowly wearing them down.
During landslides, erosion happens quickly, as large amounts of soil and rock are displaced. This is an example of a physical change.
When wind or water slows down (like in lakes or oceans), the carried sediments settle at the bottom.
Over thousands of years, these sediments get pressed and hardened to form new rocks.
These changes are slow, natural, and usually irreversible.
Points to Remember
Physical changes: Only shape, size, or state changes. No new substance is formed. Examples: Melting ice, boiling water, folding clothes.
Chemical changes: New substances are formed. Examples: Rusting, burning, lime water turning milky with carbon dioxide.
Rusting: Iron reacts with air and water to form rust — a new substance.
Combustion: Burning with oxygen produces heat and light. Needs fuel, oxygen, and enough heat (ignition temperature).
Fireflies: Glow due to a chemical change called bioluminescence, which gives light without heat.
Burning a candle:
Physical change: Wax melts and evaporates.
Chemical change: Wax vapour burns to form carbon dioxide and water.
Reversible changes: Can go back (e.g., melting ice). Irreversible changes: Cannot go back (e.g., chopping vegetables).
Desirable changes: Helpful (e.g., cooking food, making curd). Undesirable changes: Harmful (e.g., rusting, food spoilage), but some like decomposition can help make compost.
Human activities: Burning fuel and drying paint release gases that pollute the air and increase carbon dioxide.
Weathering: Rocks break into soil slowly due to temperature or water — both physical and chemical changes.
Erosion: Wind or water moves rocks and soil. It shapes the land but is often irreversible.
Michael Faraday: A scientist who used candles to explain physical and chemical changes in simple ways.
Try yourself:
What is weathering?
A.Creating new rocks from sediments.
B.A type of chemical reaction.
C.Breaking down rocks into smaller pieces.
D.The process of moving sediments.
View Solution
Difficult Words and Their Meanings
Physical Change: A change in a substance’s appearance (e.g., shape, size, state) without forming a new substance, like melting ice.
Chemical Change: A change where new substances are formed through a chemical reaction, like rusting or burning.
Chemical Reaction: A process where substances (reactants) transform into new substances (products), e.g., vinegar and baking soda forming carbon dioxide.
Rusting: A chemical change where iron reacts with air and water to form brown rust (iron oxide).
Combustion: A chemical reaction where a substance burns with oxygen, producing heat and/or light, e.g., burning magnesium.
Combustible Substance: A material that can burn, like wood, paper, or kerosene.
Ignition Temperature: The minimum temperature at which a substance catches fire, e.g., paper’s ignition temperature when heated by a matchstick.
Fire Triangle: The three requirements for combustion—fuel, oxygen, and heat (ignition temperature).
Reversible Change: A change where the original substance can be restored, e.g., freezing melted water.
Irreversible Change: A change where the original substance cannot be restored, e.g., burning wood to ash.
Desirable Change: A beneficial change, like cooking food or ripening fruits.
Undesirable Change: A harmful change, like rusting iron or food spoilage.
Weathering: The physical and chemical breakdown of rocks into soil, caused by temperature, water, or chemicals.
Erosion: The physical movement of rocks, soil, or sediments by wind or water, shaping landscapes.
Bioluminescence: Light produced by living organisms, like fireflies, through a chemical change without heat.
Yashwant and Anandi live in a village in Rajasthan. For their school project, they decided to learn about ironsmiths—people who make useful items from metals. With their grandfather’s help, they visit Sudarshan uncle, a local ironsmith, to see how he shapes iron into everyday tools like pans, buckets, and farming equipment.Curious and amazed, they begin exploring the fascinating world of metals and how they can be shaped and used.
Let’s explore the different ways metal can be used.
Properties of Materials
Properties are characteristics that help us identify and classify materials as metals or non-metals, such as their appearance, hardness, or ability to conduct heat.
Malleability
Malleability is the property of materials that allows them to be beaten into thin sheets without breaking. Beating an iron nail with a hammer
Malleability of Metals
1. Most metals, like copper, aluminium, and iron, are malleable. For example, copper and aluminium can be flattened into sheets, and iron is shaped into tools like axes.
2. Malleability is very useful in everyday life. For example:
Silver foil used to decorate sweets is made by hammering silver into extremely thin sheets.
Aluminium foil, which is commonly used for wrapping food, is produced due to aluminium’s malleability.
3. Some metals, like gold and silver, are exceptionally malleable, allowing them to be made into very thin sheets called gold leaf or silver leaf.
Some Exceptions: Soft Metals and Unique States
Not all metals are hard; some metals, like sodium and potassium, are very soft and can be easily cut using a knife. These metals are much softer than copper or iron.
Another special metal is mercury, which is liquid at room temperature, unlike most metals that are solids.
Mercury’s liquid state makes it unique and useful in devices like thermometers and barometers.
Q: How does malleability benefit everyday life? View Answer
Brittleness in Non-Metals
Unlike metals, non-metals such as coal and sulfur do not flatten when struck.
Instead, they tend to break or shatter into pieces.
This characteristic is called brittleness.
Brittle materials cannot be bent or shaped easily; they break under pressure or impact.
Behaviour of Wood
Wood behaves differently from both metals and brittle non-metals:
Wood does not flatten like metals when hit with a hammer.
At the same time, wood does not break easily like brittle non-metals.
Therefore, wood is considered neither malleable nor brittle, possessing some flexibility and toughness.
Some other properties of Metals and Non-Metals:
Metals such as copper, aluminium, and iron have a characteristic shiny appearance known as metallic lustre. This means they reflect light well, giving them a bright, polished look.
These metals are generally hard, meaning they resist scratching or denting under normal conditions.
In contrast, non-metals like coal, sulfur, and wood do not have this shiny appearance. Instead, they look dull or matte because they do not reflect light like metals.
Non-metals are usually softer compared to metals, meaning they can be scratched or broken more easily.
HOLISTIC LENS: The impact of iron on the progress of civilisation of India
In ancient India, early civilizations like the Harappans used metals such as copper and gold to make tools and jewellery. However, the widespread use of iron came much later. Iron became important because of its strength and durability. Iron tools, especially agricultural implements like ploughs, greatly helped improve farming and contributed to the progress of Indian civilization. Why do you think copper was discovered and used before iron?
Copper was discovered before iron because it occurs naturally in a pure form and has a lower melting point, making it easier to find and work with using early technology. Iron, found mostly as ore, requires higher temperatures and more advanced tools to extract and shape.
Ductility
Ductility is the property of materials that allows them to be drawn into thin wires.
Ductility of Metals
Most metals, like copper and aluminium, are ductile, used in electrical wires and ornaments like bangles and necklaces.
Gold is highly ductile, with one gram drawable into a 2-kilometer-long wire.
Everyday Uses of Ductility of Metals
Electrical Fittings: Metal wires like copper and aluminium are commonly used in electrical wiring because they conduct electricity well. You might have seen them in homes, appliances, and other electrical devices.
Jewellery and Ornaments: Many ornaments such as bangles, necklaces, and earrings are made from metal wires. These wires are shaped and twisted to create beautiful designs.
Musical Instruments: Metal wires are also used in many stringed musical instruments like the veena, sitar, violin, and guitar. The wires produce sound when plucked or bowed.
Dive Deeper: Steel Wires and Their Uses:
Steel is an alloy made from iron (metal) and carbon (non-metal). Steel wires are very strong and can support heavy loads. Due to their strength, steel wire ropes are used in important structures like suspension bridges. They are also used in cranes to lift heavy objects safely.
Q: What does ductility refer to in materials science? View Answer
Sonority
This ability of metals to produce ringing sounds is called sonority. Metals are described as sonorous materials because they can create loud and resonant sounds.
Metals: Metals like those in spoons or coins produce a ringing sound, making them sonorous. This is why school bells and ghungroos (dance bells) ring.
Non-metals: Coal and wood produce dull sounds when dropped, so they are not sonorous.
Everyday Examples of Sonority
The ringing sound of ghungroos (the small bells worn by dancers) is because of the sonorous nature of metals.
The school bell produces its loud ringing sound due to the sonority of the metal it is made from.
People can also use the difference in sound between hitting wood or metal to help navigate or identify objects, like using a stick to find their way by the sound it makes when it hits different materials.
Conduction of Heat
Conduction is the transfer of heat through a material from one point to another.
Metals: Metals like those used in cooking vessels (e.g., aluminium, copper, iron) are good conductors of heat, transferring heat quickly to cook food.
Non-metals: Wood is a poor conductor of heat, staying cooler than metal when placed in hot water, which is why vessel handles are made of wood or other poor conductors.
For example, if a metal spoon and a wooden spoon are both left in hot water for the same time, the metal spoon feels much hotter to the touch.
This is because the metal conducts heat faster from the hot water to your hand, while wood does not.
Metal and wooden spoons immersed in hot water
That’s why vessel handles are often made of wood or plastic—so that we can hold them safely without getting burned.
Conductors and Poor Conductors
The process of heat moving through a material from one point to another is called conduction.
Materials that allow heat to pass through them easily are known as conductors. Metals fall in this category.
On the other hand, materials like wood do not transfer heat well and are known as poor conductors or insulators.
Conduction of Electricity
Materials that allow electricity to flow easily are good conductors of electricity, while those that don’t are poor conductors.
Metals: Aluminium, iron, and copper are good conductors, making bulbs glow in a tester circuit, used for electrical wires.
Non-metals: Sulfur, coal, wood, stone, rubber, and nylon are poor conductors, not allowing bulbs to glow, used for insulating materials like screwdriver handles and electrician’s gloves.
Electrical Conductivity and Safety
For example, the handle of a screwdriver used by electricians is often made of plastic or rubber, which are poor conductors of electricity.
Electricians also wear rubber gloves and rubber-soled shoes while working. This is because rubber does not allow electricity to pass through easily, protecting them from electric shocks.
Conductors and Insulators
Materials that allow electricity to flow through them easily are called good conductors of electricity.
Metals such as aluminium, iron, and copper are excellent conductors and are widely used in electrical wiring and devices.
On the other hand, materials like sulfur, coal, wood, stone, rubber, and nylon do not allow electricity to flow freely and are called poor conductors of electricity or insulators.
Try yourself:
What is the property of materials that allows them to be drawn into thin wires?
A.Conductivity
B.Malleability
C.Ductility
D.Sonority
View Solution
Effect of Air and Water on Metals: Iron
Rusting of Iron:
When iron objects are left exposed to the environment, they often develop brown deposits on their surface. This phenomenon is called rusting.Rusting Iron
The brown deposits that form on iron are called rust.
Rusting is a chemical reaction where iron reacts with oxygen and moisture in the air.
This reaction causes the iron to deteriorate and weaken over time.
Conditions for Rusting:
Rusting happens only when iron comes into contact with both air and water (moist air).
Iron does not rust if it is exposed to dry air alone.
Iron also does not rust if it is submerged in water without exposure to air.
Therefore the process of rust formation, called rusting, requires both air and water, making moist air the cause of the brown deposits.
Impact
Rusting causes iron objects and structures to become weak and unsafe.
It leads to damage and decay of iron used in buildings, vehicles, bridges, and tools.
In many countries, including ours, a large amount of money is spent every year on repairing or replacing rusted iron.
Prevention of Iron from Rusting
Rusting can be prevented by several methods, such as:
Painting iron surfaces to keep air and moisture away.
Applying oil or grease to form a protective layer.
Galvanisation: Coating iron with a layer of zinc to protect it.
Q: What role do air and water play in the corrosion of iron? View Answer
Corrosion
Corrosion is the gradual deterioration of metal surfaces due to air, water, or other substances.
Fascinating Fact: The Iron Pillar of Delhi
The Iron Pillar of Delhi was built over 1600 years ago during Chandragupta II’s time. It is 8 metres tall and weighs more than 6000 kilograms. Despite facing rain, wind, and weather for centuries, it has hardly rusted. This shows how skilled ancient Indian metalworkers were in making strong and lasting iron.
Effect of Air and Water on Other Metals
1. Magnesium
Reaction with Air: When a magnesium ribbon is burned, it produces a dazzling white flame and turns into a white powder called magnesium oxide.
Nature of Oxide: Mixing magnesium oxide with warm water and testing with litmus shows it turns red litmus blue, indicating it is basic in nature.
General Rule: Oxides of metals are generally basic.
2. Sodium
Storage: Sodium is stored in kerosene to prevent it from reacting with oxygen and water in the air, as it reacts vigorously, producing a lot of heat.
Oxide Nature: Sodium oxide is basic, like other metal oxides.
Try yourself:
What causes rust to form on iron objects?
A.Exposure to sunlight
B.Exposure to water only
C.Exposure to both air and water
D.Exposure to air only
View Solution
Substances that Behave Differently from Metals in Air and Water
Certain substances, such as sulfur and phosphorus, behave very differently from metals when exposed to air and water.
Sulfur
Reaction with Air: When sulfur is burned, it produces sulfur dioxide gas, which, when dissolved in water, forms sulfurous acid.
Nature of Oxide: Testing the solution with litmus shows it is acidic, turning blue litmus red.
Reaction with Water: Sulfur does not react with water when mixed, unlike some metals.
Phosphorus
Storage: Phosphorus is stored in water because it catches fire when exposed to air.
Properties of Non-metals:
Usually soft and dull (non-lustrous) in appearance.
Not malleable or ductile, so they cannot be shaped into sheets or wires.
Not sonorous, producing dull sounds when struck.
Poor conductors of heat and electricity.
Oxides are acidic, unlike the basic oxides of metals.
Materials like plastic, glass, wood, rubber, and paper are not classified as metals or non-metals because they are not elements.
Dive Deeper: Elements (The Building Blocks of Matter)
Elements are pure substances that cannot be broken down into simpler substances by ordinary chemical methods.
Everything around us is made up of these elements.
There are currently 118 known elements.
Some elements occur naturally in the environment, such as oxygen, iron, and gold.
Others are artificially created in laboratories and do not exist naturally.
Metals and non-metals are two important sub-categories of elements.
You will learn more about elements and their properties in higher classes.
Are Non-metals Essential in Everyday Life?
While metals are very visible in daily life due to their shiny appearance, strength, and ability to conduct heat and electricity, non-metals play equally vital roles in our lives.
Importance of Non-metals
1. Oxygen is a non-metal that we breathe every day. Without oxygen, life on Earth would not survive. Other uses of oxygen include:
Used in hospitals to assist patients who have difficulty breathing.
Used in welding and combustion processes.
2. Carbon is essential because it is the building block of all life forms.
It is a key part of proteins, fats, and carbohydrates which provide energy and help in growth.
3. Nitrogen is a non-metal widely used in the manufacture of fertilizers and chemicals.
It is a vital nutrient that helps plants grow healthy and strong.
4. Chlorine is commonly used in water purification to make drinking water safe.
5. Iodine solution is applied on wounds as an antiseptic to prevent infections.
Science and Society
1. Many metals and alloys (mixtures of two or more metals or metals with non-metals) are used daily in utensils, tools, and machines.
2. Metals are essential in modern technology and almost every industry, including special fields like:
Atomic energy (e.g., zirconium)
Aerospace (e.g., titanium)
3. In India, recycling metals like iron and aluminium is common and helps to reduce waste and promote sustainability.
Try yourself:
What happens when sulfur is burned in air?
A.It becomes a metal.
B.It turns blue litmus red.
C.It produces sulfur dioxide gas.
D.It reacts with water.
View Solution
Points to Remember
Metals are shiny, hard, bendable (malleable), stretchable (ductile), make ringing sounds (sonorous), and conduct heat and electricity well.
Non-metals are usually dull, soft or brittle, and do not conduct heat or electricity well.
Malleability lets metals like copper and gold be made into thin sheets (foils, tools).
Ductility lets metals be drawn into wires for electrical use and jewelry.
Metals produce clear ringing sounds used in bells, while non-metals produce dull sounds.
Metals conduct heat, so they are used for cooking pots; non-metals like wood are used for handles because they don’t conduct heat.
Metals like copper and aluminium conduct electricity, while non-metals like rubber and plastic act as insulators for safety.
Iron rusts when exposed to both air and water, forming reddish-brown rust.
Copper and silver also get coated when exposed to air and moisture (green and black coatings).
The Iron Pillar of Delhi (1600+ years old) shows how ancient Indians made iron that doesn’t rust easily.
Magnesium burns in air forming a basic oxide; sodium is stored in kerosene to prevent reaction with air.
Sulfur burns to form sulfur dioxide, which forms acidic sulfurous acid when dissolved in water, but sulfur alone doesn’t react with water.
Non-metals like phosphorus are stored in water to stop them catching fire in air; their oxides are acidic.
Non-metals are important: oxygen for breathing, carbon for life, nitrogen for fertilizers, chlorine to clean water, iodine as medicine.
There are 118 elements, divided into metals and non-metals, some natural and some made in labs.
Metals and alloys are used in tools, machines, and industries; recycling metals like iron and aluminium helps protect the environment.
Q: What properties of metals allow them to be used in making electrical wires and tools? View Answer
Difficult Words and Their Meanings
Malleability: The ability of a material, like metal, to be beaten into thin sheets without breaking.
Ductility: The ability of a material, like metal, to be drawn into thin wires.
Sonority: The property of a material, like metal, to produce a ringing sound when struck.
Conduction: The transfer of heat or electricity through a material, like heat through a metal spoon.Metal Characteristics
Conductor: A material, like copper, that allows heat or electricity to flow easily.
Insulator: A material, like rubber, that does not allow heat or electricity to flow.
Rusting: The process where iron forms brown deposits (rust) when exposed to both air and water.
Corrosion: The gradual damage to a metal’s surface by air, water, or other substances, like rusting or green coating on copper.
Oxide: A substance formed when a metal or non-metal reacts with oxygen, like magnesium oxide or sulfur dioxide.
Element: A basic substance, like iron or oxygen, that cannot be broken into simpler substances, with 118 known types.
IntroductionIn this chapter, Nihal and his classmates are excited about their upcoming school trip to the Bhakra Nangal Dam, where they will learn how falling water is used to generate electricity at the hydroelectric power house. During the trip, they will also enjoy a scenic 13-kilometer train ride along the Sutlej river and through the Shivalik hills. Before the trip, their teacher assigns them a task to prepare a presentation on the uses of electricity. The students explore electricity’s applications in various settings—home, school, neighborhood, and city—and learn that electricity is generated from different sources, including wind, solar power, and falling water. They also realize that while electricity is essential in daily life, it must be handled carefully to avoid dangers. The chapter introduces the concept of portable sources of electricity, like batteries used in devices such as torchlights, wall clocks, and remotes.
Caution — The warning signs on electric poles and appliances remind us that electricity can be dangerous if not handled carefully. Never conduct experiments with the power supply at home or school. Even electricity from portable generators can pose a risk. For safe experimentation, use only batteries or cells, like those found in torchlights, wall clocks, radios, or remotes.
A Torchlight
What is a Torchlight?
A torchlight (also called a torch or flashlight) is a portable device that produces light, commonly used to see in the dark.
Components of a Torchlight:
Lamp: The part that produces light when the torch is turned on.
Switch: A control that turns the lamp “on” or “off”. Sliding the switch to one position makes the lamp glow, and sliding it back turns it off.
Electric Cells: Inside the torch, there are usually two or more electric cells that provide the energy to make the lamp glow.
How It Works
When the switch is in the “on” position, it connects the cells to the lamp, allowing electricity to flow and make the lamp glow. In the “off” position, the connection is broken, and the lamp stays off.
A Simple Electrical Circuit
What is an Electrical Circuit?
An electrical circuit is a complete path that allows electric current to flow from a power source (like a cell) through a device (like a lamp) and back, making the device work.
1. Electric Cell
An electric cell is a small, portable source of electrical energy, like those used in torchlights, clocks, or remotes.
1. Terminals: Every cell has two terminals:
Positive Terminal (+): Marked with a “+” sign, usually a metal cap.
Negative Terminal (-): Marked with a “-” sign, usually a flat metal disc.
2. Function: The cell provides the energy needed to make devices work by allowing current to flow from the positive to the negative terminal.
2. Battery
A battery is a combination of two or more electric cells connected together to provide more energy or last longer.
Connection: In a battery, the positive terminal of one cell is connected to the negative terminal of the next cell, forming a chain. This forms battery. Battery made up of (a) two cells (b) four cells
Example: In a torch, two cells are placed so the positive terminal of one touches the negative terminal of the other, making the lamp glow when connected properly.
Fascinating Fact
The term “battery” is often used for a single cell, like the one in a mobile phone, even though it’s technically one cell.
Electric Lamp
1. Incandescent Lamp:
Structure: An incandescent lamp has a glass bulb with a thin wire called a filament inside, supported by two thicker wires.
Terminals: The filament connects to two terminals—one at the metal case of the lamp’s base and one at the metal tip in the center.
How It Works: When electric current flows through the filament, it gets hot and glows, producing light.
Usage: Found in older torchlights, these lamps glow regardless of which terminal connects to the cell’s positive or negative terminal.
Fascinating Fact
If the filament breaks, the lamp “fuses,” stopping the current flow and preventing the lamp from glowing.
2. LED Lamp
Structure: A Light Emitting Diode (LED) lamp has no filament. It has two wires—one longer (positive terminal) and one shorter (negative terminal).An LED lamp for torch
How It Works: LEDs glow only when connected correctly, with the positive terminal (longer wire) to the battery’s positive terminal and the negative terminal (shorter wire) to the negative terminal. Current flows in one direction only.LEDs of different colours
Usage: Many modern torchlights use LEDs because they are efficient and long-lasting.
Making an Electric Lamp Glow Using an Electric Cell or Battery:
To make an electric lamp glow, we can use a simple circuit with an electric cell (or battery), an incandescent lamp, a cell holder, and some electric wires. Here’s how it works:
Electric Cell: This provides the electrical energy required to make the lamp glow. The energy comes from the chemical reaction inside the cell.
Incandescent Lamp: The lamp is a device that uses electricity to produce light. It has a filament that glows when electricity passes through it.
Cell Holder: A holder is used to securely place the electric cell in the circuit. It ensures the proper connection of the battery’s terminals to the wires.
Electric Wires: Wires are used to connect the components in the circuit. The wires allow the flow of electric current from the cell to the lamp.
How the Circuit Works:
Connection: The two terminals of the electric cell are connected to the lamp through the electric wires.
Current Flow: When the circuit is complete, the electric current flows from the negative terminal of the cell, through the wires, and into the lamp. This causes the filament inside the lamp to heat up and produce light.
Prediction of Lamp Glow: Depending on how the circuit is set up, the lamp may or may not glow. If the circuit is properly connected (with all components in place), the lamp will glow. Otherwise, it will not light up.
Electrical Circuit
A circuit is a closed loop that allows current to flow from the positive terminal of a cell, through a device (like a lamp), and back to the negative terminal.
Current Flow: Electric current is considered to flow from the positive to the negative terminal of the cell.
Incandescent Lamp: Glows when the circuit is complete, regardless of terminal connections.
LED: Glows only when terminals are correctly aligned with the battery’s terminals.
Electric Switch
A switch is a device that controls the flow of current by completing (closing) or breaking (opening) a circuit.
How It Works:
1. ON Position: The switch closes the circuit, allowing current to flow, making the lamp glow.
2. OFF Position: The switch opens the circuit, stopping the current, so the lamp doesn’t glow.
Placement: A switch can be placed anywhere in the circuit and still control the current flow.
Example: In a torch, sliding the switch to “on” completes the circuit, and sliding it to “off” breaks it.
Real-Life Switches: Home switches for lights work similarly but are designed differently for safety and convenience.
Circuit Diagrams
What is a Circuit Diagram?
A circuit diagram is a drawing that uses standard symbols to represent the components of an electrical circuit, making it easy to understand how the circuit is built.
Symbols for Components:
Electrical components and their symbols
Purpose Circuit diagrams simplify complex circuits, making them easier to draw and understand.
Dive Deeper – Standardization
International organizations like the International Electrotechnical Commission (IEC), American National Standards Institute (ANSI), and the Institute of Electrical and Electronics Engineers (IEEE) create standard symbols used worldwide, ensuring everyone understands the same diagrams.
Electrical Conductors and Insulators
Materials are classified based on whether they allow electric current to flow through them.
Conductors
Materials that allow electric current to flow easily are called conductors or good conductors of electricity.
Examples: Metals like copper, silver, gold, aluminum, and objects like keys, coins, and sewing needles.
Use in Circuits: Conductors, especially copper, are used for wires because they allow current to flow efficiently.
Dive Deeper – Best Conductors:
Silver, copper, and gold are the best conductors, but copper is used most often due to its lower cost and availability.
Insulators
Materials that do not allow electric current to flow are called insulators or poor conductors of electricity.
Examples: Plastic, rubber, glass, wood, cork, paper, wax, ceramics, and objects like plastic scales, erasers, and candles.
Use in Circuits: Insulators are used to cover wires, make plug tops, and switches to prevent electric shocks and ensure safety.
(a) Conduction tester (b) Using the conduction tester for testing a materialHere are the results of testing materials for electrical conductivity:
Importance of Both:
Conductors: Used in wires, switches, plugs, and sockets to carry current.
Insulators: Protect users from electric shocks by covering conductive parts.
Caution: The human body is a conductor, so electric current passing through it can cause severe injury or death. Never touch switches or plugs with wet hands, use devices in wet areas, or handle damaged electrical equipment.
Dive Deeper – Types of Electricity:
Direct Current (DC): Produced by batteries, used in small devices like torchlights and phones.
Alternating Current (AC): Supplied from power plants to wall sockets, used for larger appliances.
Points to Remember
An electric cell provides portable electrical energy and has a positive terminal (metal cap, +) and a negative terminal (metal disc, -).
A battery is formed by connecting two or more cells, with the positive terminal of one cell touching the negative terminal of the next, to supply more energy or last longer.
The term “battery” is sometimes used for a single cell, like in mobile phones.
An incandescent lamp has a filament that glows when heated by current, connected to two terminals (metal case and tip), and glows regardless of terminal connections.
A “fused” incandescent lamp doesn’t glow because its filament is broken, stopping current flow.
An LED has no filament, only glows when its positive terminal (longer wire) connects to the battery’s positive terminal and negative terminal (shorter wire) to the negative terminal, as current flows in one direction.
A switch completes (ON) or breaks (OFF) a circuit, controlling current flow, and can be placed anywhere in the circuit.
An electrical circuit is a closed path for current, flowing from the positive to the negative terminal of a cell, making devices like lamps glow.
Circuit diagrams use standard symbols (e.g., long/short lines for cell terminals, triangle for LED) set by organizations like IEC, ANSI, and IEEE, making circuits easy to understand globally.
Conductors (e.g., copper, silver) allow current to flow and are used for wires, while insulators (e.g., plastic, rubber) block current and are used for safety coverings.
Copper is widely used for wires due to its good conductivity, lower cost, and abundant supply compared to silver or gold.
The human body conducts electricity, so handling electrical devices unsafely (e.g., with wet hands) can cause injury or death.
Battery-powered devices use Direct Current (DC), while wall sockets supply Alternating Current (AC) for larger appliances.
Difficult Words and Their Meanings
Electricity: A form of energy that powers devices, like lights or fans, by flowing through wires or circuits.
Circuit: A complete path that allows electric current to flow from a power source (like a cell) through a device and back.
Electric Cell: A small, portable device that produces electrical energy, with positive and negative terminals, used in torchlights or remotes.
Battery: Two or more electric cells connected together to provide more energy or last longer.
Terminal: The ends of a cell or device (positive or negative) where current enters or leaves.
Incandescent Lamp: A light bulb with a filament that glows when heated by electric current, used in older torchlights.
Filament: A thin wire inside an incandescent lamp that glows to produce light when current passes through it.
LED (Light Emitting Diode): A modern lamp that glows when current flows in one direction, with no filament, used in many torchlights.
Switch: A device that controls current by opening (stopping) or closing (allowing) a circuit.
Conductor: A material, like metal, that allows electric current to flow easily, used for wires.
Insulator: A material, like plastic or rubber, that blocks electric current, used to cover wires for safety.
Circuit Diagram: A drawing using standard symbols to show how electrical components are connected in a circuit.
On 28 February, the school celebrated National Science Day with a science fair. At the entrance, Ashwin and Keerthi were given plain white sheets of paper. They were puzzled—why a blank sheet?
Soon, a volunteer sprayed a liquid on their sheets, and like magic, the words “Welcome to the Wonderful World of Science” appeared! This amazing trick made them very curious.
At the Colourful World of Substances stall, they saw many experiments where mixing things changed their colour. Excited to learn more, they decided to explore the science behind it.
Let’s join them on this fun journey!
Nature – Our Science Laboratory
We can determine if a substance is acidic, basic, or neutral by using special tools called indicators, which change color or smell when mixed with different substances.
1. Litmus as an Indicator
What is Litmus? Litmus is a natural material obtained from lichens, which are organisms formed by a fungus and an alga living together, often found on rocks and trees in rainy, clean areas.
Forms of Litmus: It is available as blue and red litmus paper strips, used to test substances.
How Litmus Works:
If a substance turns blue litmus paper red, it is acidic.
If a substance turns red litmus paper blue, it is basic.
If there’s no color change in either litmus paper, the substance is neutral.
Here are the test results showing the nature of samples using blue and red litmus papers.
Try yourself:
What does blue litmus paper turning red indicate?
A.The substance is acidic.
B.The substance is basic.
C.The substance is neutral.
D.The substance is colorful.
View Solution
Properties of Acids and Bases
Acids:
Taste sour, like lemon juice, tamarind, or vinegar.
Contain specific acids, e.g., citric acid in lemon, lactic acid in curd, tartaric acid in tamarind, acetic acid in vinegar.
Turn blue litmus red and red rose extract red.
Bases:
Feel slippery or soapy when rubbed, like baking soda solution or soap.
Often taste bitter, but not all bitter things are bases (e.g., bitter gourd is not basic).
Turn red litmus blue, red rose extract green, and turmeric paper red.
Neutral Substances:
Do not have a strong taste or slippery feel.
Do not change the color of indicators like litmus, red rose extract, or turmeric.
2. Red Rose as an Indicator
Preparation of Red Rose Extract Red rose extract is prepared by collecting fresh rose petals and washing them properly. The petals are then crushed and soaked in hot water. After some time, the mixture is filtered to get a red-colored liquid known as red rose extract.
How It Works:
In acidic substances, the extract changes to a shade of red.
In basic substances, it changes to a shade of green.The changes in colour of the red rose extract on adding lemon juice (A) and soap solution (B)
In neutral substances, the extract’s color remains unchanged.
Red rose extract is an acid-base indicator because it shows different colors for acidic and basic substances, similar to litmus.
Some examples:
Lemon juice (acidic) turns the extract red.
Soap solution (basic) turns it green.
Neutral substances like sugar solution don’t affect the color.
Try yourself:
What color does red rose extract turn in basic substances?
A.Red
B.Green
C.Yellow
D.Blue
View Solution
3. Turmeric as an Indicator
Preparation
Turmeric powder is mixed with water to make a paste, spread on filter paper, and dried to create yellow turmeric paper strips.
How It Works:
Basic substances turn turmeric paper red.
Acidic and neutral substances do not change the yellow color of turmeric paper.
A turmeric stain on a shirt changes color when soap (basic) is applied, showing its indicator property.
Turmeric paper can only identify basic substances, not distinguish between acidic and neutral ones.
Here are the test results showing the nature of samples using turmeric paper:
Fascinating Facts: Why is Turmeric Called the ‘Golden’ Spice?
Turmeric, also known as Haldi, is a bright yellow spice that belongs to the ginger family. Grown widely in India and other countries, it’s a common ingredient in everyday cooking. But turmeric is much more than just a flavouring agent!
In the Ayurvedic system of medicine, turmeric is believed to offer several health benefits. That’s why it plays a key role in many traditional home remedies. Its rich golden color and healing properties have earned it the name ‘Golden Spice’.
Researchers today are also studying turmeric for its potential benefits beyond taste and color—making this age-old spice even more special!
4. Olfactory Indicators
Olfactory indicators are special substances whose smell changes when they come in contact with acidic or basic substances.
For example, a cloth soaked in onion juice loses its smell when mixed with tamarind water (which is acidic) or baking soda solution (which is basic).
These indicators are useful because they help us identify whether a substance is acidic or basic just by observing changes in smell.
5. Other Natural Indicators
Substances like beetroot, purple cabbage, red hibiscus (gudhal), and Indian blackberry (jamun) can also act as acid-base indicators, changing colors in acidic or basic solutions.
Did You Know ?
Hydrangea plants in the Himalayas or North-eastern states produce blue flowers in acidic soil and pink or red flowers in basic soil, showing how soil nature affects plants.
Know a Scientist: Acharya Prafulla Chandra Ray
Acharya Prafulla Chandra Ray is known as the Father of Modern Indian Chemistry. He earned his chemistry doctorate in the UK and later returned to India. In 1901, he started India’s first pharmaceutical company.
He wrote about the history of Indian science to show the world the achievements of ancient Indian scientists. A true reformer, he also supported teaching in the mother tongue to make education easier and more meaningful.
Let’s Revise
Q: How does turmeric act as a natural indicator? View Answer
Q: What are olfactory indicators and how do they work? View Answer
What Happens When Acidic Substances Mix with Basic Substances?
1. Neutralization Process
When an acid (e.g., lemon juice) is mixed with a base (e.g., lime water) in the right amount, they react to form a solution that is neither acidic nor basic.
This reaction is called neutralization.
Neutralization shows how acids and bases balance each other, creating a neutral substance that doesn’t affect indicators.
This process is key to understanding how substances interact chemically.
Activity
Let’s see how acids and bases react using litmus solution:
First, add lemon juice (which is acidic) to a blue litmus solution. It turns red, showing the presence of an acid.
Now, slowly add lime water (a base) to the same solution. As more base is added, the red color starts changing back to blue, showing the solution is becoming neutral or basic.
This happens because the base cancels the effect of the acid, resulting in a neutral solution.
2. Products of Neutralization
The reaction produces salt, water, and releases heat.
Acid + Base → Salt + Water + Heat.
Neutralization in Daily Life
Situation 1: Ant Bite
When a red ant bites, it injects formic acid into the skin, causing redness and a stinging pain.
Applying moist baking soda, which is a base, neutralizes the formic acid, relieving the pain and reducing swelling.
Different regions may use other basic remedies, like lime water, for ant bites.
Situation 2: Soil Treatment
Farmers may notice poor plant growth if the soil becomes too acidic due to excessive use of chemical fertilizers.
Adding lime (a base, like calcium oxide) neutralizes the acidic soil, making it suitable for plant growth.
If the soil is too basic, organic matter like manure or composted leaves is added, which releases acids to neutralize the basic soil.
Neutral soil may still need nutrients if plants are unhealthy, showing that soil health involves more than just acidity or basicity.
Situation 3: Factory Waste
Acidic waste from factories can pollute lakes, harming fish and other aquatic life.
Before releasing waste into lakes, basic substances are added to neutralize the acidity, making the water safe for fish.
Q: What is a neutralization reaction and what are its products? View Answer
Q: How does baking soda help relieve pain from an ant bite? View Answer
Points to Remember
Substances are grouped into acidic, basic, or neutral based on how they interact with indicators.
Litmus, from lichens, comes as blue and red paper: acids turn blue litmus red, bases turn red litmus blue, and neutral substances cause no change.
Red rose extract, made from crushed petals, turns red in acidic solutions and green in basic solutions, acting as an acid-base indicator.
Turmeric paper, prepared from turmeric paste, turns red in basic solutions but remains yellow in acidic or neutral solutions, making it useful only for detecting bases.
Olfactory indicators, like onion-soaked cloth, change smell when mixed with acidic or basic substances, helping identify their nature.
Other natural indicators, such as beetroot, purple cabbage, red hibiscus, and Indian blackberry, also show color changes in acidic or basic solutions.
Acids taste sour (e.g., lemon juice contains citric acid, vinegar contains acetic acid) and turn blue litmus red.
Bases feel slippery, often taste bitter, and turn red litmus blue, red rose extract green, and turmeric paper red.
Neutral substances, like tap water or sugar solution, don’t change the color or smell of indicators.
Neutralization is the reaction between an acid and a base, forming salt, water, and releasing heat, resulting in a neutral solution.
Neutralization is used in daily life to:
Relieve ant bites by applying baking soda to neutralize formic acid.
Treat acidic soil with lime or basic soil with organic matter to help plants grow.
Neutralize acidic factory waste to protect aquatic life in lakes.
Hydrangea flowers change color based on soil: blue in acidic soil, pink or red in basic soil, showing nature’s use of acid-base properties.
Creative uses, like writing messages with basic solutions on turmeric paper, show how indicators can be applied in art or communication.
Difficult Words and Their Meanings
Acidic: A substance that tastes sour, turns blue litmus paper red, and red rose extract red, like lemon juice or vinegar.
Basic: A substance that feels slippery, turns red litmus paper blue, red rose extract green, and turmeric paper red, like soap or baking soda.
Neutral: A substance that doesn’t affect indicators’ color or smell and is neither acidic nor basic, like sugar solution or tap water.
Indicator: A tool that changes color or smell to show if a substance is acidic, basic, or neutral, such as litmus, red rose extract, or turmeric.
Litmus: A natural substance from lichens, used as blue or red paper strips to test if a substance is acidic (turns blue litmus red) or basic (turns red litmus blue).
Lichens: Organisms made of a fungus and an alga living together, found on rocks and trees, used to make litmus.
Neutralization: A chemical reaction where an acid and base mix to form salt, water, and heat, creating a neutral solution.
Olfactory: Related to the sense of smell, used for indicators like onion that change odor in acidic or basic substances.
Extract: A liquid obtained by crushing and soaking a substance (like red rose petals) in water and filtering it, used as an indicator.
Formic Acid: An acidic substance injected by ants during a bite, causing pain and redness, which can be neutralized by a base like baking soda.
When light passes through aligned holes in a straight line, it creates a bright spot on a screen.
If the holes are misaligned, no spot appears, indicating that light does not bend around obstacles.
The movement of water and minerals can be demonstrated by placing plant twigs in colored water, where the color travels up the stem and into leaves and flowers.
An experiment with soaked moong bean seeds shows that carbon dioxide is released during respiration, which turns lime water milky.
This breakdown happens in a long tube called the alimentary canal, which starts at the mouth and ends at the anus.Human Digestive System
Food moves down the oesophagus by a wave-like motion called peristalsis, where the walls of the food pipe contract and relax gently.Movement of food in the food pipe
In 1822, Alexis St. Martin was accidentally shot in the stomach, leaving a small permanent hole after treatment.
After leaving the stomach, partially digested food enters the small intestine, which is about 6 meters long, making it the longest part of the alimentary canal.Alimentary canal if it is stretched out
The lining has thousands of finger-like projections called villi, which increase the surface area for efficient absorption.
Millets such as jowar, bajra, and ragi are good alternatives because they are naturally gluten-free.
The large intestine is about 1.5 meters long, shorter but wider than the small intestine.
Birds lack teeth but have a special stomach chamber called the gizzard.
For example, during the COVID-19 pandemic, the SARS-CoV-2 virus affected the respiratory system.
Model of Mechanism of Breathing
Two test tubes with equal amounts of fresh lime water are taken.(a) Air is passed into lime water with a pichkari/syringe (b) Air is exhaled into lime water
To solve this, the sinking bowl water clock (called Ghatika-yantra) was developed and mentioned by Aryabhata and other astronomical texts.
A simple pendulum
Gently hold the bob, pull it slightly to one side, and release it without pushing. Make sure the string is taut when you release it.
Does the mass of the bob affect the time period?
For example, in a 100-metre race, all runners start together but soon spread out.Boys running a race on a straight track
The distance covered by an object in a unit time is called its speed.
Another instrument called an odometer measures the total distance travelled by the vehicle in kilometres.
Example: Car moving from one point to another at constant speed.
Example: Car moving from A to B and C to D with changing speeds.
This is because the air layer between blankets slows down heat loss from our body, making us feel warm and cozy.
To keep houses warm in such harsh conditions, people build walls with two wooden layers.
The warmth we feel around the flame and pan is due to radiation.
This continuous movement of water—evaporation, condensation, precipitation, infiltration, and runoff—is called the water cycleWater cycle
The ice stupa melts slowly in spring, supplying water for farming and other needs throughout summer.Ice Stupa
Girls may also experience slight changes in their voice.
Acne is common and happens when oil blocks skin pores.
These changes are part of growing up.
Use sanitary pads or reusable cloth pads to stay clean and comfortable.
Today, biodegradable sanitary pads are also available, which are safe for the environment.
Lime Water Turns Milky
Candle (a) burning (b) covered with a glass tumbler
Paper catching fire
View Answer
Metals such as copper, aluminium, and iron have a characteristic shiny appearance known as metallic lustre. This means they reflect light well, giving them a bright, polished look.
In contrast, non-metals like coal, sulfur, and wood do not have this shiny appearance. Instead, they look dull or matte because they do not reflect light like metals.
Electrical Fittings:
Jewellery and Ornaments:
Musical Instruments:
The ringing sound of ghungroos (the small bells worn by dancers) is because of the sonorous nature of metals.
The school bell produces its loud ringing sound due to the sonority of the metal it is made from.
People can also use the difference in sound between hitting wood or metal to help navigate or identify objects, like using a stick to find their way by the sound it makes when it hits different materials.
On the other hand, materials like sulfur, coal, wood, stone, rubber, and nylon do not allow electricity to flow freely and are called poor conductors of electricity or insulators.
Metal Characteristics
Battery made up of (a) two cells (b) four cells 
An LED lamp for torch
LEDs of different colours
Electric Cell: This provides the electrical energy required to make the lamp glow. The energy comes from the chemical reaction inside the cell.
Incandescent Lamp: The lamp is a device that uses electricity to produce light. It has a filament that glows when electricity passes through it.
Cell Holder: A holder is used to securely place the electric cell in the circuit. It ensures the proper connection of the battery’s terminals to the wires.
Prediction of Lamp Glow: Depending on how the circuit is set up, the lamp may or may not glow. If the circuit is properly connected (with all components in place), the lamp will glow. Otherwise, it will not light up.
The changes in colour of the red rose extract on adding lemon juice (A) and soap solution (B)
