03. Very Short Question Answer: Atoms and Molecules

Q1: What is the building block of all matter?
Ans:
 Atom is the building block of all matter.

Q2: Give the derivation source of the symbol of sodium (Na).
Ans: 
The symbol of ‘Na’ for sodium is derived from its Latin name ‘Natrium’.

Q3: What is the measuring unit of atomic radius?
Ans:
 Nanometer (nm) is the measuring unit of atomic radius.

Q4: Who stated the Law of Constant Proportion?
Ans: 
Joseph Louis Proust stated the Law of Constant Proportion.

Q5: What is the full form of IUPAC?
Ans: 
International Union of Pure and Applied Chemistry.

Q6: Name the instrument which produces an image of the surface of an element that shows atoms.
Ans: 
Scanning tunnelling microscope.

Q7: Who was the first scientist to give the concept of the formation of compounds?
Ans: 
Antoine L. Lavoisier gave the concept of the formation of compounds.

Q8: Give the full form of amu?
Ans: 
The full form of amu is atomic mass unit.

Q9: State the law of conservation of mass.
Ans: 
This law states that mass can neither be created nor destroyed in a chemical reaction. That is, the mass of reactants is always equal to the mass of products.

Q10: Who introduced the word ‘Mole’?
Ans: 
‘Wilhelm Ostwald’ introduced the word ‘Mole’.

Q11: What is Avogadro’s Constant?
Ans:
 The number of particles present in one mole of any substance is fixed with a value of 6.022 × 1023.

Q12: Give two examples of triatomic molecules.
Ans: 
Carbon dioxide (CO2) and water (H2O).

Q13: Define valency.
Ans:
 The combining power of an element to attain the noble gas configuration is called valency. Or, it is defined as the number of electrons lost or gained by an atom to acquire noble gas configuration.

Q14: Name any two monatomic atoms.
Ans: 
Sodium, Aluminium.

Q15: What is the latest short form of the atomic mass unit?
Ans: 
The latest short form of the atomic mass unit is u, according to IUPAC.

Q16: What do we get if 3 atoms of oxygen unite into a molecule, instead of the usual 2?
Ans: 
We get (O3) ozone.

Q17: How does an atom exist?
Ans: 
Atom exists in the form of atom, molecule, or ions.

Q18: Give difference between 2H and H2.
Ans: 
2H indicates 2 atoms of hydrogen, and H2 indicates one molecule of hydrogen.

Q19: How did the scientist lay the foundation of chemical sciences? Name the scientist.
Ans:
 Antoine Laurent Lavoisier laid the foundation of chemical science by establishing two important laws of chemical combination.

Q20: Define law of conservation of mass.
Ans: 
Law of conservation of mass states that, ‘Mass is neither created nor destroyed in a chemical reaction.’

Q21: Define law of constant proportion.
Ans:
 Law of constant proportion states that, ‘In a pure chemical substance, the elements are always present in definite proportions by mass.’

Q22: Which organization approves the names of elements all over the world?
Ans: 
International Union of Pure and Applied Chemistry (IUPAC).

Q23: Write the symbols of tungsten and iron.
Ans: 
(i) Tungsten (W) and (ii) Iron (Fe)

Q24: Name two atoms which exist as independent atoms.
Ans:
 Noble gases such as argon (Ar) and helium (He) exist as independent atoms.

Q25: Define atomicity.
Ans:
 The number of atoms present in one molecule of an element or a compound is known as its atomicity.

02. Very Short Question Answer: Is Matter Around Us Pure

Q1: Name the process by which pure copper sulphate can be obtained from its impure sample.
Ans:
 Crystallisation is the process used to obtain pure copper sulphate from an impure sample.

Q2: What is a homogeneous mixture of two or more substances called?
Ans:
 A solution is a homogeneous mixture in which the solute is uniformly distributed in the solvent, so the composition is the same throughout.

Q3: What is the component of a solution that is present in a smaller proportion called?
Ans: 
The solute is the component of a solution that is present in a smaller proportion and is dissolved by the solvent.

Q4: Naphthalene and sand can be separated by the process of
Ans: 
The separation of naphthalene from sand can be achieved through the process of sublimation, because naphthalene changes directly from solid to vapour on heating while sand does not.

Q5: What is an element made up of?
Ans:
 An element is made up of only one type of atom; for example, carbon (C) and iron (Fe) each consist of only one kind of atom.

Q6: What type of mixture is Milk of Magnesia?
Ans:
 Milk of Magnesia is a suspension, not a true solution; it contains fine solid particles dispersed in a liquid which may settle on standing.

Q7: Give two examples of colloids from your daily life.
Ans:
 Examples of colloids are milk (liquid dispersed in liquid) and fog (tiny liquid droplets dispersed in air).

Q8: Name the constituents of German silver.
Ans: 
German silver is an alloy made of copper, zinc, and nickel.

Q9: What is the meaning of the ‘concentration of a solution’?
Ans:  
Concentration of a solution is the amount of solute dissolved in a specified amount of solvent or solution; a greater amount of dissolved solute means a higher concentration.

Q10: Name the process used to separate liquids which have a difference in boiling points of less than 25°C.
Ans:
 Fractional distillation is used to separate such liquids; it employs a fractionating column to separate components with close boiling points.

Q11: Name two categories of pure substances.
Ans: 
The two categories of pure substances are an element and a compound.

Q12: Define the term Solvent.
Ans:
 A solvent is the component of a solution present in larger amount that dissolves the solute to form the solution.

Q13: What are two types of matter on the basis of composition?
Ans: 
Pure substances and mixtures are the two main types of matter based on composition.

Q14: Name the types of mixtures.
Ans: 
The two types of mixtures are homogeneous mixtures (uniform composition) and heterogeneous mixtures (non-uniform composition).

Q15: Give natural examples of a mixture.
Ans: 
Examples of natural mixtures include seawatermineral ores and soil, all of which contain a variety of substances combined together.

Q16: Name a metal that is liquid at room temperature.
Ans: 
Mercury is the only metal that is liquid at ordinary room temperature.

Q17: What is the principle of separation?
Ans:
 The principle of separation is based on differences in physical or chemical properties of components, such as boiling pointsolubilityparticle size or magnetic properties, and using these differences to separate them.

Q18: Give an example of a liquid and a liquid-type solution.
Ans: 
Vinegar is a liquid solution made of acetic acid dissolved in water.

Q19: Define dispersion medium.
Ans:
 The dispersion medium is the component present in excess in a colloid that acts as the medium in which the colloidal particles are dispersed.

Q20: Define the term heterogeneous mixture.
Ans:
 A heterogeneous mixture is one in which the components are not uniformly distributed and different parts of the mixture show different properties.

01. Very Short Question Answer: Matter in Our Surroundings

Q1: A rubber band is a solid, but it can change its shape. Why?
Ans:
 A rubber band changes shape under force and regains the shape when the force is removed, this is due to less intermolecular force of attraction between the particles.

Q2: When salt or sugar is poured into different kinds of vessels, why do they take the shape of vessel as they are solid?
Ans: 
Salt or sugar takes the shape of containing vessel, but does not change its individual shape. For example : Sugar crystal is cubical and they remain cubical in any vessel.

Q3: We can easily move our hand in the air but to do the same through a solid block of wood. We need a karate expert. Why?
Ans: 
In air, the inter-particle attractive forces are negligible and hence, it is easy to separate the particles in air and we can easily move our hand in air. The interparticle forces are very strong in solids. So, it is not easy to separate the particles and it is not easy to move our hand through a solid block of wood.

Q4: Express the boiling point of water in Celsius as well as Kelvin scale.
Ans: 
100°C and 373 K.

Q5: What is dry ice?
Ans:
 Solid carbon dioxide obtained by cooling and applying pressure on carbon dioxide gas. It does not melt so it is called dry ice.

Q6: What is normal atmospheric pressure?
Ans: 
The atmospheric pressure at sea level is 1 atmosphere and taken as the normal atmospheric pressure.

Q7: Give the temperature at which water exists in two different phases/states.
Ans: 
(i) At 0°C water can be in solid or in liquid state. (ii) At 100°C water can be in liquid or in gaseous state.

Q8: Define matter.
Ans:
 Anything that occupies space and has mass and is felt by senses is called matter.

Q9: Give state of a matter if this substance has neither a fixed shape nor a fixed volume.
Ans:
 Gas.

Q10: What do you mean by vapour?
Ans:
 A substance that is found in gaseous state only at room temperature is called vapour.

Q11: Name any two substances which sublime.
Ans: 
Camphor and naphthalene.

Q12: Which is the slow process, evaporation or boiling?
Ans: 
Evaporation.

Q12: Write the SI unit of temperature?
Ans:
 Kelvin.

Q13: Convert 10°C into Kelvin scale.
Ans:
 273 + 10 = 283 K

Q14: Name two processes from which it may be concluded that the particles of a gas move continuously.
Ans: 
Compressibility and Brownian movement.

Zig-Zag movement of Particles

Q15: What is common among the three states of matter?
Ans:
 They all contain molecules.

Q16: A substance x is highly compressible and could easily be liquefied. It can also take the shape of the container. Guess the nature of the substance.
Ans:
 Gas.

Q17: Is it possible to turn a liquid into vapour without heating?
Ans:
 Yes, by the process of evaporation as evaporization of water occur below the boiling point under atmospheric pressure.

Q18: When we put CuSO4 in water, after some time we find the solution turns blue. Why? Also, on heating it, what change will occur?
Ans:
 The solution turns blue because of diffusion. On heating the solution, nothing will happen.

Q19: The boiling point of alcohol is 78°C. What is this temperature on Kelvin scale?
Ans: 
K = °C + 273 = 78 + 273 = 351 K

Q20: Why are light and sound not considered as matter?
Ans:
 Light and sound are not considered as matter because they have no mass and do not occupy space.

Q21: We can get the smell of perfume sitting several metres away, why?
Ans: 
This is because perfumes diffuse very fast and can reach to people sitting several metres away.

Q22: Sponge is a solid, yet we are able to compress it. Why?
Ans: 
Sponge has very small holes throughout its structure. These holes are filled with air. When it is compressed, the air in the holes is squeezed out. Thus, we are able to compress it.

Q23: What is plasma?
Ans:
 Plasma is a state of matter consisting of super excited particles of very high energy level.

Q24: Define melting point.
Ans:
 The temperature at which a solid melts to become liquid at the atmospheric pressure is called its melting point.

Q25: What is humidity?
Ans:
 The air holds water vapour, this air with water is called humid air and the amount of water vapour present in the air is called humidity.

12. Worksheet Solutions: Improvement in Food Resources

Multiple Choice Questions

Q1. Which of the following is a Kharif crop?
(a) Wheat
(b) Mustard
(c) Soyabean
(d) Gram

Correct Answer is   Option (c)
Soyabean is a Kharif crop grown during the monsoon season.

Q2. What is the main objective of crop variety improvement?
(a) To increase water availability
(b) To make crops resistant to diseases
(c) To reduce the maturity duration
(d) All of the above

Correct Answer is   Option (d)
Crop variety improvement focuses on increasing yields, resistance to diseases, and reducing maturity duration.

Q3. Which farming practice involves growing two or more crops in definite row patterns?
(a) Mixed farming
(b) Intercropping
(c) Crop rotation
(d) Agroforestry

Correct Answer is   Option (b)
Intercropping is the practice of growing two or more crops in definite row patterns.

Q4. What is a major challenge in composite fish culture?
(a) Increased fish yield
(b) Availability of good-quality fish seed
(c) High water consumption
(d) Overfishing

Correct Answer is   Option (b)
The lack of availability of good-quality fish seed is a challenge in composite fish culture.

Q5. Which nutrient is supplied by air to plants?
(a) Nitrogen
(b) Phosphorus
(c) Carbon
(d) Potassium

Correct Answer is   Option (c)
Air supplies carbon and oxygen to plants.

Q6. What is the primary purpose of cross-breeding in cattle farming?
(a) To increase milk production
(b) To improve resistance to diseases
(c) To improve meat quality
(d) To improve lactation period

Correct Answer is   Option (a)
Cross-breeding improves milk production in cattle.

Q7. What is the process of composting?
(a) Growing plants to enrich the soil
(b) Decomposition of waste materials in pits
(c) Using fertilizers to improve soil quality
(d) The use of pesticides to protect crops

Correct Answer is   Option (b)
Composting is the process of decomposing waste materials in pits to produce organic matter for enriching soil.

Q8. Which type of manure is prepared by using earthworms?
(a) Green manure
(b) Compost
(c) Vermi-compost
(d) Bio-manure

Correct Answer is   Option (c)
Vermi-compost is made by using earthworms to hasten the decomposition process.

Q9. Which of the following is a method used to increase food production in India?
(a) Green Revolution
(b) White Revolution
(c) Both a and b
(d) None of the above

Correct Answer is   Option (c)
Both the Green and White Revolutions have helped increase food production in India.

Q10. What is the main aim of organic farming?
(a) To increase the use of chemical fertilizers
(b) To use minimal or no chemicals and maximum organic manures
(c) To focus on large-scale production
(d) To use genetically modified crops

Correct Answer is   Option (b)
Organic farming focuses on minimal chemical use and maximum organic manures.

Q11. Which of the following crops is an example of a Rabi crop?
(a) Pigeon pea
(b) Cotton
(c) Wheat
(d) Maize

Correct Answer is   Option (c)
Wheat is a Rabi crop grown during the winter season.

Q12. What is a key feature of composite fish culture?
(a) It involves only one species of fish
(b) It uses multiple species with different food habits
(c) It requires a high salt concentration
(d) It is only done in marine waters

Correct Answer is   Option (b)
Composite fish culture uses multiple species with different food habits to increase the yield.

Q13. What type of irrigation is most commonly used in India?
(a) Canal irrigation
(b) Rain-fed irrigation
(c) River irrigation
(d) Wells

Correct Answer is   Option (b)
Most agriculture in India is rain-fed, meaning dependent on rainfall.

Q14. What is the primary goal of nutrient management in crops?
(a) To increase the water supply
(b) To improve plant growth
(c) To enhance soil fertility
(d) Both b and c

Correct Answer is   Option (d)
Nutrient management focuses on improving both plant growth and soil fertility.

Q15. What is the role of bees in agriculture?
(a) Pollination
(b) Honey production
(c) Pest control
(d) All of the above

Correct Answer is   Option (d)
Bees play an important role in pollination, honey production, and pest control.

Fill in the blanks

1. Matter is made up of small ______.

Correct Answer is   Particles

2. The forces of attraction between the particles are ______ in solids, ______ in liquids, and ______ in gases.

Correct Answer is   Maximum, intermediate, minimum

3. ______ is the change of gaseous state directly to solid state without going through liquid state.

Correct Answer is   Deposition or Desublimation

4. In intercropping, crops are grown in ______ patterns.

Correct Answer is   Definite row

5. The process of composting involves the decomposition of organic waste in ______.

Correct Answer is   Pits

6. ______ is the method of enriching soil by growing certain plants and then ploughing them into the soil.

Correct Answer is   Green manure

7. ______ is a popular marine fish caught off the Indian coastline.

Correct Answer is   Mackerel

8. Organic farming focuses on using minimal or no ______ and maximum organic manures.

Correct Answer is   Chemicals

9. The process of hybridization involves the crossing of ______ plants.

Correct Answer is   Genetically dissimilar

10. Fish farming in freshwater is known as ______.

Correct Answer is   Inland fisheries

11. ______ are essential nutrients required by plants in large quantities.

Correct Answer is   Macronutrients

12. Crop rotation involves the growing of different crops in a pre-planned ______.

Correct Answer is   Succession

13. ______ is the main source of protein from fish.

Correct Answer is   Fish meat

14. In cattle farming, animals used for milk production are called ______.

Correct Answer is   Milch animals

15. ______ is the management of livestock for the purpose of breeding, feeding, and disease control.

Correct Answer is   Animal husbandry

Very Short Answer Question

Q.1. What has green revolution led to?

Ans: Increased food grain production. 

Q.2. What has white revolution led to?

Ans: Increased production and more efficient management of milk.

Q.3. Name the two factors on which food security depends.

Ans: Availability of food and access to it

Q.4. What should we do for a sustained livelihood?

Ans: We should adopt practices like mixed farming, intercropping and integrated farming practices.

Q.5. Which food items primarily supply proteins?

Ans: Pulses like gram, peas, lentils, etc.

Q.6. Name any two fodder crops.

Ans: Berseem and Sudan grass

Q.7. What is the duration of kharif season?

Ans: From the month of June to October

Q.8. What is the duration of Rabi season?

Ans: From the month of November to April

Q.9. What is the name given to crops obtained by introducing a gene that provides the desired characteristic?

Ans: Genetically modified crops

Q.10. What is the main benefit of mixed cropping?

Ans: It reduces production risk and gives insurance against failure of all the crops.

Short Answer Types Questions

Q.1. What are the hazards of using fertilizers?

Effects of using fertilizers:

  • Effect on soil quality: continued use of fertilizers leads to a loss of organic matter, a deterioration of soil structure.
  • Eutrophication: Excessive use of fertilizers build up nitrates on the soil.

Nitrates and phosphates are washed by rain and carried to lakes, ponds and rivers and causes excessive growth of plants of algae. Algae deplete the oxygen content of the water body.


Q.2. What are the main practices involved in keeping of animals or animal husbandry?

Main practices involved in animal husband day:

  • Breeding – It is done to obtain animals with desired characters. Breeding can develop high milk yielding and high meat-yielding animals.
  • Feeding – It deals with the study of proper food (called feed), mode and time of feeding of different animals.
  • Weeding – It is elimination of uneconomical animals.
  • Heeding – It means the proper care and management of animals.


Q.3. How do good animal husbandry practices benefit farmers?

Animal husbandry is the scientificmanagement of animal livestock. It includesvarious aspects such as feeding, breeding anddisease control.
As the population increases and asliving standards increase, the demand formilk, eggs and meat is also going up. Also,the growing awareness of the need for proper treatment of livestock has broughtin new limitations in livestock farming. Thus,livestock production also needs to beimproved. This improvement can be brought about by good animal husbandry practices like providing good food and preventing diseases in the cattles that will benefit farmers to obtain better quality and quantity products.


Q.4. What is hybridization?

Hybridization refers to the crossing between genetically dissimilar plants. In this method, the two crop verities are selected, each with at least one of desired characteristics such as high-yield or resistance to disease.


Q.5. For increasing production, what is common in poultry, fisheries and bee-keeping?

For increasing production, steps that are common in poultry, fisheriesand bee-keeping are as follows :

  • Good varieties/breeds are used.
  • Good nutritious food is provided.
  • Hygienic conditions/cleanliness is taken care of


Q.6. How do biotic and abiotic factors affect crop production?

The biotic factors include living organisms like honey bees and earthworms who help in better crop production while pests(insects and rodents) and microbes that produce bad effect on crop production.

The abiotic factors are the climatic conditions and non living natural resources like soil, water and air. They also affect crop production since favourable conditions of temperature, humidity and mineral nutrition improve crop production.


Q.7. What factors may be responsiblefor losses of grains duringstorage?

Factors that may be responsiblefor losses of grains duringstorage are :

  • Abiotic factors: Unfavourable conditions of humidity and temperature.
  • Biotic factors: Insects, rodents, bacteria, fungi etc that feed on grains.


Q.8. Why should preventive measures and biological control methods bepreferred for protecting crops?

Prevention is better than cure so is true for plants also. Such preventions involve spraying of herbicides, weedicides, insecticides, pesticides, fungicides etc in the crop field.
Since their excessive use can harm the crop plants and cause pollution so proper seed bed preparation, timelysowing of crops, intercropping and croprotation are additionally applicable. Other than these biological control methods like use of resistant varieties is highly useful.


Q.9. What is pasturage and how is it related to honey production?

Pasturage refers to the flowers availableto the bees for nectar and pollen collection.The value or quality of honey depends upon the pasturage. Along with this the kind of flowers available will determine the taste of the honey.

Q.10. Differentiate between compost and vermicompost.

Compost: It is prepared by the process in which farm waste materials like livestock excreta, vegetable wastes, animal refuse, domestic waste, straw, eradicated weeds are decomposed and used as manure. 
Vermicompost: It is the compost prepared from organic matter using earthworms which hasten the process of decomposition. 

12. Worksheet: Improvement in Food Resources

Multiple Choice Questions

Q1. Which of the following is a Kharif crop?
(a) Wheat
(b) Mustard
(c) Soyabean
(d) Gram

Q2. What is the main objective of crop variety improvement?
(a) To increase water availability
(b) To make crops resistant to diseases
(c) To reduce the maturity duration
(d) All of the above

Q3. Which farming practice involves growing two or more crops in definite row patterns?
(a) Mixed farming
(b) Intercropping
(c) Crop rotation
(d) Agroforestry

Q4. What is a major challenge in composite fish culture?
(a) Increased fish yield
(b) Availability of good-quality fish seed
(c) High water consumption
(d) Overfishing

Q5. Which nutrient is supplied by air to plants?
(a) Nitrogen
(b) Phosphorus
(c) Carbon
(d) Potassium

Q6. What is the primary purpose of cross-breeding in cattle farming?
(a) To increase milk production
(b) To improve resistance to diseases
(c) To improve meat quality
(d) To improve lactation period

Q7. What is the process of composting?
(a) Growing plants to enrich the soil
(b) Decomposition of waste materials in pits
(c) Using fertilizers to improve soil quality
(d) The use of pesticides to protect crops

Q8. Which type of manure is prepared by using earthworms?
(a) Green manure
(b) Compost
(c) Vermi-compost
(d) Bio-manure

Q9. Which of the following is a method used to increase food production in India?
(a) Green Revolution
(b) White Revolution
(c) Both a and b
(d) None of the above

Q10. What is the main aim of organic farming?
(a) To increase the use of chemical fertilizers
(b) To use minimal or no chemicals and maximum organic manures
(c) To focus on large-scale production
(d) To use genetically modified crops

Q11. Which of the following crops is an example of a Rabi crop?
(a) Pigeon pea
(b) Cotton
(c) Wheat
(d) Maize

Q12. What is a key feature of composite fish culture?
(a) It involves only one species of fish
(b) It uses multiple species with different food habits
(c) It requires a high salt concentration
(d) It is only done in marine waters

Q13. What type of irrigation is most commonly used in India?
(a) Canal irrigation
(b) Rain-fed irrigation
(c) River irrigation
(d) Wells

Q14. What is the primary goal of nutrient management in crops?
(a) To increase the water supply
(b) To improve plant growth
(c) To enhance soil fertility
(d) Both b and c

Q15. What is the role of bees in agriculture?
(a) Pollination
(b) Honey production
(c) Pest control
(d) All of the above

Fill in the blanks

1. Matter is made up of small ______.

2. The forces of attraction between the particles are ______ in solids, ______ in liquids, and ______ in gases.

3. ______ is the change of gaseous state directly to solid state without going through liquid state.

4. In intercropping, crops are grown in ______ patterns.

5. The process of composting involves the decomposition of organic waste in ______.

6. ______ is the method of enriching soil by growing certain plants and then ploughing them into the soil.

7. ______ is a popular marine fish caught off the Indian coastline.

8. Organic farming focuses on using minimal or no ______ and maximum organic manures.

9. The process of hybridization involves the crossing of ______ plants.

10. Fish farming in freshwater is known as ______.

11. ______ are essential nutrients required by plants in large quantities.

12. Crop rotation involves the growing of different crops in a pre-planned ______.

13. ______ is the main source of protein from fish.

14. In cattle farming, animals used for milk production are called ______.

15. ______ is the management of livestock for the purpose of breeding, feeding, and disease control.

Very Short Answer Question 

Q.1. What has green revolution led to? 

Q.2. What has white revolution led to?

Q.3. Name the two factors on which food security depends.

Q.4. What should we do for a sustained livelihood?

Q.5. Which food items primarily supply proteins?

Q.6. Name any two fodder crops.

Q.7. What is the duration of Kharif season?

Q.8. What is the duration of Rabi season?

Q.9. What is the name given to crops obtained by introducing a gene that provides the desired characteristic?

Q.10. What is the main benefit of mixed cropping?

Short Answer Types Questions

Q.1. What are the hazards of using fertilizers?

Q.2. What are the main practices involved in keeping of animals or animal husbandry?

Q.3. How do good animal husbandry practices benefit farmers?

Q.4. What is hybridization?

Q.5. For increasing production, what is common in poultry, fisheries and bee-keeping?

Q.6. How do biotic and abiotic factors affect crop production?

Q.7. What factors may be responsiblefor losses of grains duringstorage?

Q.8. Why should preventive measures and biological control methods bepreferred for protecting crops?

Q.9. What is pasturage and how is it related to honey production?

Q.10. Differentiate between compost and vermicompost.

11. Worksheet Solutions: Sound

Q.1. Fill in the blanks

(i) Quality of sound depends on Waveform .
(ii) The speed of sound in a solid is greater than the speed of sound in air.
(iii) Sound is caused by Vibrations .
(iv) Pitch of sound depends on frequency .
(v) Sound cannot travel through Vacuum .


Q.2. If 25 sound waves are produced per second, what is the frequency in hertz?
(a) 25 hertz
(b) 50 hertz
(c) 75 hertz
(d) 1/25 hertz

Ans: (a)

Explanation: Frequency is the number of waves produced per second. If 25 waves are produced each second, the frequency is 25 hertz, written as 25 Hz.


Q.3. Which of the following vibrates when a musical note is produced by the cymbals in an orchestra?
(a) Stretched strings
(b) Stretched membranes
(c) Metal plates
(d) Air columns

Ans: (c)

Explanation: Cymbals are thin metal plates that vibrate when struck. These vibrations of the metal plates set the surrounding air into motion and produce sound. Stretched strings and membranes vibrate in instruments like guitars and drums, and air columns vibrate in wind instruments, so those options are not correct for cymbals.


Q.4. Inner Ear is called as
(a) Cochlea
(b) Pinna
(c) Hammer
(d) Anvil

Ans: (a)

Explanation: The inner ear is called the cochlea; it is the spiral-shaped part that helps convert sound vibrations into nerve signals. The pinna is the outer ear, while the hammer and anvil are small bones in the middle ear.


Q.5. Frequency of ultrasonic sound wave is
(a) Greater than 20 HZ
(b) Greater than 20,000 HZ
(c) Greater than 2 HZ
(d) Greater than 2 MHZ

Ans: (b)

Explanation: Ultrasonic sound waves have frequencies greater than 20,000 Hz (20 kHz). Options (a) and (c) describe much lower frequencies; option (d) (greater than 2 MHz) is far above the ultrasonic threshold but does not define the general ultrasonic range.


Q.6. Why are the ceilings of concert halls curved?

Ans: The ceilings of concert halls are curved so that sound reflections are spread evenly throughout the hall. Curved surfaces help direct and disperse sound waves to reach all corners, improving clarity and loudness for the entire audience.


Q.7. What happens when sound travels in air?

Ans: When sound travels through air it creates alternating regions of compression and rarefaction. In a compression the air particles are closer together and the pressure is higher; in a rarefaction the particles are farther apart and the pressure is lower. These successive compressions and rarefactions move through the air and carry the sound to the listener.


Q.8. What is an echo? Name two areas of its application?

Ans: An echo is the reflected sound heard when sound waves strike a surface and return to the listener. Two applications of echoes are SONAR (used to detect objects under water) and using reflected ultrasound to detect flaws in metal objects (ultrasonic testing).


Q.9. What is SONAR? Write its working?

Ans: SONAR stands for Sound Navigation and Ranging. It uses ultrasonic waves to locate objects under water. A transmitter sends out ultrasonic pulses; these pulses travel through water, strike an object and get reflected back. A detector receives the reflected waves and converts them into electrical signals. By measuring the time between sending the pulse and receiving the echo, the distance to the object is calculated using the relation distance = (speed of sound in water × time taken)/2.


Q.10. How can ultrasound be used to detect the defect in metal block?

Ans: Ultrasound (waves with frequency greater than 20 kHz) is sent into the metal from one end while detectors are placed at the other end or at positions to receive returned echoes. If the metal has no defect, the ultrasound passes through and is detected as expected. If there is a defect, part of the ultrasound is reflected back or attenuated at the defect, so the detector receives a changed signal (weaker, delayed or missing). Such changes indicate the presence and often the location of the defect; this is the basis of ultrasonic non-destructive testing.


Q.11. Suppose you and your friend are on the moon. Will you be able to hear any sound produced by your friend?

Ans: No. There is no air on the Moon, so there is no medium to carry sound waves. Therefore you and your friend would not be able to hear sounds produced by one another; communication on the Moon requires radio or other electronic means.


Q.12. Sound requires a medium to travel? Justify experimentally.

Ans: The following experiment demonstrates that sound requires a medium for propagation:

  • Take a bell jar and suspend an electric bell in it,
  • The bell jar is connected to a vacuum pump. Till the air is in the bell jar, the sound of the electric bell is louder.
  • Now, with the help of vacuum pump, pump out the air gradually
  • Now as air is pumped out, the sound of the bell gets fainter and fainter.
  • Now, when the bell jar is completely vacuumed no sound is heard.
  • This shows that air is required for propagation of sound.

Explanation: As air is removed from the jar the bell becomes fainter and finally silent in a vacuum, showing that air (a medium) is needed to transmit sound.


Q.13. How does the sound produced by a vibrating object in a medium reach your ear?

Ans: A vibrating object pushes and pulls the particles of the surrounding medium. These particles transfer the disturbance to neighbouring particles as alternating compressions and rarefactions. The chain of particle vibrations travels through the medium until the waves reach the ear, where they make the eardrum vibrate and are perceived as sound.


Q.14. Why are sound waves called as mechanical waves?

Ans: Sound waves are called mechanical waves because they require a material medium (solid, liquid or gas) to travel. Without a medium, sound cannot propagate, which is a defining property of mechanical waves.


Q.15. Explain how sound is produced by your school bell.

Ans: When the peon strikes the school bell with a hammer, the bell metal vibrates. These vibrations disturb the air around the bell, creating compressions and rarefactions that travel as sound waves. The sound waves reach our ears and are heard as the ringing of the bell.

11. Worksheet: Sound

Q.1. Fill in the blanks
(i) Quality of sound depends on ________ .
(ii) The speed of sound in a solid is ________ than the speed of sound in air.
(iii) Sound is caused by _________.
(iv) Pitch of sound depends on ________.
(v) Sound cannot travel through _______.

Q.2. If 25 sound waves are produced per second, what is the frequency in hertz?
(a) 25 hertz
(b) 50 hertz
(c) 75 hertz
(d) 1/25 hertz

Q.3. Which of the following vibrates when a musical note is produced by the cymbals in an orchestra?
(a) Stretched strings
(b) Stretched membranes
(c) Metal plates
(d) Air columns

Q.5. Frequency of ultrasonic sound wave is
(a) Greater than 20 HZ
(b) Greater than 20,000 HZ
(c) Greater than 2 HZ
(d) Greater than 2 MHZ

Q.6. Why are the ceilings of concert halls curved?

Q.7. What happens when sound travels in air?

Q.8. What is an echo? Name two areas of its application?

Q.9. What is SONAR? Write its working?

Q.10. How can ultrasound be used to detect the defect in metal block?

Q.11. Suppose you and your friend are on the moon. Will you be able to hear any sound produced by your friend?

Q.12. Sound requires a medium to travel? Justify experimentally.

Q.13. How does the sound produced by a vibrating object in a medium reach your ear?

Q.14. Why are sound waves called as mechanical waves?

Q.15. Explain how sound is produced by your school bell.

10. Worksheet Solutions: Work and Energy

Q.1. Fill in the blank

(i) When a ball is thrown upwards, kinetic energy is transformed into potential energy.
(ii) The sum of the potential and kinetic energies of a body is called mechanical energy.
(iii) Work is measured as a product of force and distance.
(iv) The electricity meter installed in our home measures electric energy in the units of kWh.
(v) The work done on a body moving in a circular path is zero.

Q.2. How are Joule (J) and ergs (erg) related?
(a) 1J = 107erg
(b) 1erg = 107J
(c) 1J = 107erg
(d) None

Ans: (a)
Explanation: 1 joule is equal to 107 erg. This follows from the definitions: 1 J = 1 N·m and 1 erg = 1 dyne·cm, and the conversion between SI and CGS units gives 1 J = 107 erg.

Q.3. If the force is applied at an angle θ then work done is
(a) W = FS Cos θ  F = Force
(b) W = FS θ S =  Distance
(c) W = FS Sin  θ W = work
(d) None

Ans: (a)
Explanation: Only the component of the force along the direction of displacement does work. If the force F makes an angle θ with the displacement S, the component along S is F cos θ, so work W = (F cos θ) × S = FS cos θ.

Q.4. If a body is stored at a height ‘h’ then it will posses:
(a) Kinetic energy
(b) Potential energy
(c) Both
(d) None

Ans: (b)
Explanation: A body stored at a height h above a reference level has gravitational potential energy. Its potential energy is given by mgh (where m is mass, g is acceleration due to gravity and h is height). If the body is not moving, its kinetic energy is zero.

Q.5. If the body starts from rest, then change in its kinetic energy is
(a) Positive
(b) Negative
(c) Zero
(d) May be Positive or negative depending upon the mass of the body

Ans: (a)
Explanation: If a body starts from rest and later moves, its speed becomes greater than zero. Kinetic energy (½mv2) increases from zero to a positive value, so the change in kinetic energy is positive.

Q.6. When do we say that work is done?

Ans: Work is done when a force acts on an object and the object undergoes a displacement that has a component along the direction of the force.

Q.7. Define 1 J of work.

Ans: One joule is the work done when a force of 1 N moves an object through a distance of 1 m in the direction of the force.

Q.8. What is the kinetic energy of an object?

Ans: Kinetic energy is the mechanical energy possessed by an object because of its motion. For a mass m moving with speed v, its kinetic energy is ½mv2.

Q.9. What is power?

Ans: Power is the rate at which work is done or energy is transferred. It is denoted by P.
Explanation: P = W / t, where W is work done and t is the time taken. The SI unit of power is watt, where 1 watt = 1 J/s.

Q.10. An object thrown at a certain angle to the ground moves in a curved path and falls back to the ground. The initial and the final points of the path of the object lie on the same horizontal line. What is the work done by the force of gravity on the object?

Ans: The work done by the force of gravity on the object over the whole motion is zero.
Explanation: Gravity is a conservative force. The work done by gravity equals the change in gravitational potential energy. If the initial and final heights are the same, the change in potential energy is zero, so the net work done by gravity over the complete path is zero.

Q.11. Illustrate the law of conservation of energy by discussing the energy changes which occur when we draw a pendulum bob to one side and allow it to oscillate. Why does the bob eventually come to rest? What happens to its energy eventually? Is it a violation of the law of conservation of energy?

Ans: When the bob is pulled to one side, it gains maximum gravitational potential energy and negligible kinetic energy. As it is released and passes through the lowest point, potential energy is converted into kinetic energy, giving it maximum speed there. As it climbs to the other side, kinetic energy converts back into potential energy. This interchange of potential and kinetic energy continues during oscillation.
The bob eventually comes to rest because non-conservative forces, such as air resistance and friction at the support, remove mechanical energy from the system. The mechanical energy is transformed into thermal energy (heat) and slight sound, which spread into the surroundings. This is called dissipation of energy.
This is not a violation of the law of conservation of energy, because the total energy (mechanical plus thermal and other forms) remains constant; energy only changes from one form to another.

Q.12. Define average power.

Ans: Average power is the total work done or total energy consumed divided by the total time taken. Average power is defined as average amount of work done by a body per unit time. Mathematically, average power = total work / total time.

Q.13.  In each of the following a force, F is acting on an object of mass, m. The direction of displacement is from west to east shown by the longer arrow. Observe the diagrams carefully and state whether the work done by the force is negative, positive or zero.

Ans:

  • In the first diagram the force is perpendicular to the displacement, so the work done is zero.
  • In the second diagram the force acts in the same direction as the displacement, so the work done is positive.
  • In the third diagram the force acts opposite to the displacement, so the work done is negative.

Q.14. Define 1 watt of power.

Ans: One watt is the power when work is done at the rate of 1 J/s. In other words, 1 W = 1 J/s.

Q.15. A battery lights a bulb. Describe the energy changes involved in the process.

Ans: Chemical energy stored in the battery is converted into electrical energy in the circuit. When the current passes through the bulb, electrical energy is transformed into light energy and heat energy (thermal energy) in the bulb’s filament.

10. Worksheet: Work and Energy

Q.1. Fill in the blank
(i) When a ball is thrown upwards, ________ energy is transformed into ________ energy.
(ii) The sum of the potential and kinetic energies of a body is called ________ energy.
(iii) Work is measured as a product of ________ and _________.
(iv) The electricity meter installed in our home measures electric energy in the units of ______.
(v) The work done on a body moving in a circular path is ___________.

Q.2. How are Joule (J) and ergs (erg) related?
(a) 1J = 107erg
(b) 1erg = 107J
(c) 1J = 107erg
(d) None

Q.3.  If the force is applied at an angle θ then work done is
(a) W = FS Cos θ  F = Force
(b) W = FS θ S =  Distance
(c) W = FS Sin  θ W = work
(d) None

Q.4. If a body is stored at a height ‘h’ then it will posses:
(a) Kinetic energy
(b) Potential energy
(c) Both
(d) None

Q.5. If the body starts from rest, then change in its kinetic energy is
(a) Positive
(b) Negative
(c) Zero
(d) May be Positive or negative depending upon the mass of the body

Q.6. When do we say that work is done?

Q.7. Define 1 J of work.

Q.8. What is the kinetic energy of an object?

Q.9. What is power?

Q.10. An object thrown at a certain angle to the ground moves in a curved path and falls back to the ground. The initial and the final points of the path of the object lie on the same horizontal line. What is the work done by the force of gravity on the object?

Q.11. Illustrate the law of conservation of energy by discussing the energy changes which occur when we draw a pendulum bob to one side and allow it to oscillate. Why does the bob eventually come to rest? What happens to its energy eventually? Is it a violation of the law of conservation of energy?

Q.12. Define average power.

Q.13.  In each of the following a force, F is acting on an object of mass, m. The direction of displacement is from west to east shown by the longer arrow. Observe the diagrams carefully and state whether the work done by the force is negative, positive or zero.

Q.14. Define 1 watt of power.

Q.15. A battery lights a bulb. Describe the energy changes involved in the process.

09. Worksheet Solutions: Gravitation

Multiple Choice Questions

Q1: If the area of an object is less than the pressure acting on that object will be
(a) Less
(b) More
(c) Independent of area
(d) None of the above
Ans: (b)
Explanation: Pressure is defined as force divided by area (P = F / A). For a given force, if the area decreases the value of P increases. Therefore, when the area is smaller, the pressure on the object is greater.

Q2: Even though stone also attracts earth towards itself, earth does not move
(a) Because of greater mass of earth
(b) Because of lesser mass of stone
(c) Force exerted by stone is less
(d) Force exerted earth is large
Ans: (a)
Explanation: The stone and Earth attract each other with equal forces (Newton’s third law). However, acceleration = force/mass. Because the Earth has a very large mass, the acceleration produced in Earth by the stone’s pull is extremely small and thus not noticeable.

Q3: Which of the statements is correct?
(a) Mass is constant and weight is variable
(b) Mass is variable and weight is constant.
(c) Both Mass and weight are variable
(d) Both Mass and weight are constant.
Ans: (a)
Explanation: Mass is an intrinsic property of matter and does not change with location. Weight is the force due to gravity on that mass (W = mg) and depends on the local gravitational acceleration g, so weight can change with place (for example, on the Moon or at different heights).

Q4: Weight of the object is:
(a) More at the equator and less at poles
(b) More at poles and less at equator
(c) Same at poles and equator
(d) Depend on Mass of the object
Ans: (b)
Explanation: Effective weight depends on local gravitational acceleration. Two factors make weight slightly greater at the poles than at the equator: (i) centrifugal effect of Earth’s rotation reduces apparent gravity at the equator, and (ii) Earth is slightly flattened at the poles which affects g. Hence weight is more at the poles and less at the equator for the same mass.

Q5: An object is put one by one in three liquids having different densities. The object floats with 1/9, 2/11 and 3/7 parts of their volumes outside the liquid surface in liquids of densities d1, d2 and d3respectively. Which of the following statement is correct?
(a) d1 > d2 > d3
(b) d1 > d2 < d3
(c) d1 < d2 > d3
(d) d1 < d2 < d3
Ans: (a)
Explanation: If a fraction fout of volume is outside, the submerged fraction is 1 – fout. The submerged fraction is proportional to the liquid’s density (for the same object). Submerged fractions here are 8/9 (≈0.889), 9/11 (≈0.818), and 4/7 (≈0.571). These numbers show d1 > d2 > d3, so option (a) is correct.

Q6: In the relation F = GM mld2, the quantity G
(a) depends on the value ofg at the place of observation
(b) is used only when the Earth is one of the two masses
(c) is greatest at the surface of the Earth
(d) is universal constant of nature
Ans: (d)
Explanation: G is the universal gravitational constant. Its value does not depend on location, nor on the masses involved. It is the same for all pairs of masses anywhere in the universe.

Q7: Law of gravitation gives the gravitational force between
(a) the Earth and a point mass only
(b) the Earth and Sun only
(c) any two bodies having some mass
(d) two charged bodies only
Ans: (c) 
Explanation: Newton’s law of universal gravitation applies to any two masses anywhere: it gives the mutual gravitational force between any pair of masses, not only Earth-related pairs.

Q8: The value of quantity G in the law of gravitation
(a) depends on mass of Earth only
(b) depends on radius of Earth only
(c) depends on both mass and radius of Earth
(d) is independent of mass and radius of the Earth
Ans: (d) 
Explanation: The universal constant G is independent of the properties of Earth or any other body. It is a fundamental constant of nature and has the same value everywhere.

Q9: Two particles are placed at some distance. If the mass of each of the two particles is doubled, keeping the distance between them unchanged, the value of gravitational force between them will be
(a) 1/4 times
(b) 4 times
(c) 1/2 times
(d) unchanged
Ans: (b)
Explanation: Gravitational force  If both masses are doubled, the product m1 × m2 becomes 4 times larger, so the force becomes 4 times the original.

Q10: The atmosphere is held to the Earth by
(a) gravity
(b) wind
(c) clouds
(d) Earth’s magnetic field
Ans: (a)
Explanation: The atmosphere is retained around the Earth because of Earth’s gravitational attraction on air molecules. Wind or clouds do not hold the atmosphere; Earth’s magnetic field affects charged particles but not the neutral gases of the atmosphere.

Fill in the blank

(i) The value of g on the earth is about Six times of that on the moon.
(ii) In fluids (liquids and gases), pressure acts in All directions, and pressure increases as the depth increases.
(iii) If the area of a snow shoe is five times Bigger than the area of an ordinary shoe, then the pressure of a snow shoe on the snow is five times smaller.
(iv) Force acting on a unit area is called Pressure.
(v) The weight of an object on the earth is about Six times of its weight on the moon.

Crossword

Across

3. Quantity of matter contained in a body
4. The property due to which a body immersed in fluid experiences upward force.
5. Acceleration due to gravity of moon is how much time that of Earth
7. Whenever objects fall towards the Earth under gravitational force alone, we say that objects are in
8. The force with which a body is attracted towards the Earth
10. Force of gravitation due to Earth is called
11. Nature of gravitational force is always

Down

1. Force between two bodies due to their masses
2. Thrust on unit area
6. Mass per unit volume
9. SI unit of pressure

Ans:

Across:
3. Mass
4. Buoyancy
5. One sixth
7. Free fall
8. Weight
10. Gravity
11. Attractive

Down:
1. Gravitational force
2. Pressure
6. Density
9. Pascal

Very Short Answer Questions

Q1: A man of mass 60 Kg is standing on the floor holding a stone weighing 40 N. What is the force with which the floor is pushing him up?
Ans: The gravitational pull on the man = Mg
= 60 × 10 = 600 N
The weight he is carrying (stone) = 40 N
Total downward force on the floor = 600 N + 40 N = 640 N
By Newton’s third law and equilibrium, the floor pushes the man upward with a force of 640 N.

Q2: State Archimedes Principle?
Ans: According to Archimedes’ principle, when a body is partially or completely immersed in a fluid, it experiences an upthrust (buoyant force) equal to the weight of the fluid displaced by the body.

Q3: Why does a block of plastic released under water come up to the surface of water?
Ans: The density of the plastic is less than the density of water. Therefore the buoyant force on the plastic (which depends on the fluid displaced) is greater than the weight of the plastic, and the net upward force makes the block rise to the surface and float.

Q4: Why will a sheet of paper fall slower than one that is crumpled into a ball?
Ans: A flat sheet of paper has a much larger surface area facing the air, so it experiences greater air resistance (drag). This larger opposing force slows its fall. A crumpled ball has a smaller area and encounters less air resistance, so it falls faster.

Q5: Why is it difficult to hold a schoolbag having a strap made of a thin and strong string?
Ans: A thin strap concentrates the bag’s weight on a small area of the shoulder. Pressure = force / area, so a smaller contact area gives a larger pressure on the shoulder, which feels painful and makes it difficult to hold.

Q6: What makes a body to float or sink in a liquid?
Ans:

  • When an object is immersed in a liquid, it experiences its weight acting downward and an upthrust (buoyant force) from the liquid acting upward.
  • If the weight of the body is greater than the upthrust, the object sinks.
  • If the weight of the body is less than the upthrust, the object floats.
  • If the weight equals the upthrust, the object remains neutrally buoyant (suspends at that depth).

Q7: What is the importance of universal law of gravitation?
The universal law of gravitation is important due to the following:
Ans:

  • This law explains why objects stay on Earth – the force that binds us to Earth.
  • It describes the motion of planets around the Sun and satellites around planets.
  • It accounts for the tides on Earth caused by the gravitational pull of the Moon and Sun.
  • It explains why the Moon moves around the Earth under gravitational attraction.

Q8: What happens to the force between two objects, if
(i) The mass of one object is doubled?
(ii) The distance between the objects is doubled and tripled?
(iii) The masses of both objects are doubled?
Ans:

(i) The force between two objects will be doubled (force ∝ product of masses).
(ii) If distance is doubled, force becomes 1/4 of the original (since force ∝ 1 / r2). If distance is tripled, force becomes 1/9 of the original.
(iii) If both masses are doubled, the force becomes 4 times the original (product of masses increases by 4).

Q9: State the universal law of gravitation.
According to Newton’s universal law of gravitation:
Ans: Every mass in the universe attracts every other mass with a force that is directly proportional to the product of their masses and inversely proportional to the square of the distance between their centres.

Q10: What do you mean by buoyancy?
Ans: Buoyancy (or upthrust) is the upward force experienced by an object when it is wholly or partially immersed in a fluid. It equals the weight of the fluid displaced by the object.