50 Physics Objective Questions on Heat Energy, Temperature & Kinetic Theory (With Answers and Explanations)

This set of 50 multiple-choice questions is designed to test and reinforce understanding of fundamental concepts in heat energy, temperature, and the kinetic molecular theory. Based on the senior secondary physics curriculum and suitable for JAMB, WAEC, NABTEB, and other examinations, the questions cover definitions, effects of heat, differences between heat and temperature, molecular behaviour in solids, liquids, and gases, and the explanation of thermal expansion. Detailed solutions and explanations are provided for all questions to aid learning and make this a valuable resource for both students and educators.

50 Physics Objective Questions on Linear, Area and Volume Expansivity (With Answers and Solutions)

Questions

1. Heat energy is best defined as theA. degree of hotness of a bodyB. total internal energy of a body

   C. energy that flows only from cold to hot bodies

   D. measure of average kinetic energy of molecules

2. Heat flows naturally from aA. cold body to a hot bodyB. body at lower temperature to one at higher temperature

   C. body at higher temperature to one at lower temperature

   D. body with less internal energy to one with more internal energy

3. Temperature is defined as theA. total internal energy of a bodyB. degree of hotness or coldness of a body

   C. amount of heat in a body

   D. average kinetic energy of molecules

4. The SI unit of temperature is theA. degree Celsius (°C)B. degree Fahrenheit (°F)

   C. Kelvin (K)

   D. Joule (J)

5. Which of the following instruments is used to measure temperature?A. CalorimeterB. Thermometer

   C. Barometer

   D. Hygrometer

6. When two bodies at different temperatures are placed in contact, heat will flow untilA. both bodies have the same internal energyB. the colder body becomes warmer than the other

   C. both bodies reach the same temperature

   D. all the heat is transferred to the surroundings

7. Which of the following physical quantities determines the direction of flow of heat energy when two bodies are placed in contact?A. MassB. Volume

   C. Temperature

   D. Density

8. Which of the following is NOT an effect of heat on a substance?A. Change in temperatureB. Change of state

   C. Decrease in mass

   D. Thermal expansion

9. When a solid is heated and changes to a liquid, the process is calledA. freezingB. melting

   C. condensation

   D. sublimation

10. The emission of electrons from the surface of a hot metal is known asA. photoelectric emissionB. thermionic emission

    C. field emission

    D. secondary emission

11. When a gas is heated at constant volume, its pressureA. decreasesB. remains constant

    C. increases

    D. becomes zero

12. According to the kinetic molecular theory, matter is made up of tiny particles calledA. atoms onlyB. molecules

    C. electrons

    D. protons

13. Which of the following is an assumption of the kinetic molecular theory?A. Molecules are stationary.B. There are no forces between molecules.

    C. Molecules are in constant random motion.

    D. The volume of gas molecules is large compared to the container.

14. In solids, intermolecular forces areA. negligibleB. very weak

    C. very strong

    D. absent

15. Liquids haveA. definite shape and definite volumeB. definite volume but no definite shape

    C. no definite volume but definite shape

    D. neither definite shape nor definite volume

16. Gases assume the shape and volume of their container becauseA. intermolecular forces are very strongB. molecules are in fixed positions

    C. intermolecular forces are negligible

    D. molecules are larger than in solids

17. According to the kinetic theory, the temperature of a body is a measure of theA. total kinetic energy of its moleculesB. average kinetic energy of its molecules

    C. potential energy of its molecules

    D. number of molecules

18. When heat is added to a substance, the speed of its moleculesA. decreasesB. remains the same

    C. increases

    D. becomes zero

19. Which of the following statements correctly distinguishes heat from temperature?A. Heat is a fundamental quantity while temperature is a derived quantity.B. Heat is measured in Kelvin while temperature is measured in Joules.

    C. Heat is the total internal energy while temperature is the degree of hotness.

    D. Heat determines the direction of flow of thermal energy.

20. The clinical thermometer is an example of aA. gas thermometerB. mercury-in-glass thermometer

    C. thermocouple

    D. resistance thermometer

21. Thermal expansion is theA. decrease in size of an object when cooledB. increase in size of an object when heated

    C. change of state from solid to liquid

    D. increase in pressure of a gas at constant volume

22. When a solid is heated and expands, its moleculesA. move closer togetherB. vibrate with smaller amplitude

    C. gain kinetic energy and move farther apart

    D. lose kinetic energy

23. Thermal expansivity is greatest inA. solidsB. liquids

    C. gases

    D. all states equally

24. Intermolecular forces are strongest inA. gasesB. liquids

    C. solids

    D. plasma

25. Which of the following statements about solids, liquids, and gases is correct?A. Only gases have molecules in constant motion.B. Solids have no intermolecular forces.

    C. Molecules in solids vibrate about fixed mean positions.

    D. Liquids have definite shape.

26. The degree of expansion of a unit size of a material when its temperature is raised by one unit is calledA. heat capacityB. thermal conductivity

    C. thermal expansivity

    D. specific heat capacity

27. Which of the following is an example of a physical property that can change when a body is heated?A. MassB. Density

    C. Number of molecules

    D. Atomic number

28. When heat is removed from a gas, it may change to a liquid. This process is calledA. evaporationB. condensation

    C. freezing

    D. sublimation

29. A kettle of cold water placed on a burning stove becomes hot becauseA. the water generates its own heatB. heat flows from the stove to the water

    C. the stove absorbs cold from the water

    D. the water temperature equalizes with the room

30. The SI unit of heat energy is theA. Kelvin (K)B. Joule (J)

    C. Watt (W)

    D. Calorie (cal)

31. Which of the following statements is NOT correct according to the kinetic molecular theory?A. Molecules of a gas are in constant random motion.B. The volume of gas molecules is negligible compared to the container.

    C. Collisions between gas molecules are inelastic.

    D. There are attractive forces between molecules.

32. In which state of matter do molecules have the highest kinetic energy at a given temperature?A. SolidB. Liquid

    C. Gas

    D. All states have the same kinetic energy

33. A solid has a definite shape and volume becauseA. its molecules are far apartB. intermolecular forces are very strong

    C. it has no intermolecular forces

    D. its molecules are in random motion

34. The kinetic molecular theory explains that an increase in temperature leads toA. a decrease in the average kinetic energy of moleculesB. an increase in the average kinetic energy of molecules

    C. no change in molecular motion

    D. a decrease in the number of molecules

35. The difference between the molecules of ice, water, and water vapour is mainly in theirA. chemical structureB. intermolecular distances and forces

    C. atomic composition

    D. mass

36. Which of the following statements is NOT correct?A. Molecules of ice, water, and water vapour have equal intermolecular distances.B. The structure of water molecules does not differ among ice, water, and water vapour.

    C. Water vapour molecules attract each other with forces far less than those between water molecules.

    D. Water is less compressible than water vapour.

37. When a body loses heat, its temperatureA. risesB. falls

    C. remains constant

    D. becomes negative

38. Thermometers are usually graduated inA. Kelvin scale onlyB. Celsius scale

    C. Fahrenheit scale only

    D. Joule scale

39. The commonest type of thermometer in laboratories is theA. thermocouple thermometerB. gas thermometer

    C. mercury-in-glass thermometer

    D. resistance thermometer

40. Which of the following is a correct assumption of the kinetic theory?A. Molecules are at rest at absolute zero.B. The volume of liquid molecules is negligible.

    C. Collisions between gas molecules are perfectly elastic.

    D. There are no forces between molecules.

41. The property of a body that determines the direction of heat flow when in contact with another body is itsA. heat capacityB. internal energy

    C. mass

    D. temperature

42. When a metal rod is heated, it undergoesA. only linear expansionB. only volume expansion

    C. expansion in all dimensions

    D. contraction

43. The increase in length of a solid when heated is described by itsA. cubic expansivityB. superficial expansivity

    C. linear expansivity

    D. absolute expansivity

44. Area expansivity is also known asA. linear expansivityB. superficial expansivity

    C. cubic expansivity

    D. volumetric expansivity

45. The symbol for cubic expansivity isA. α (alpha)B. β (beta)

    C. γ (gamma)

    D. λ (lambda)

46. The S.I unit of linear expansivity isA. KB. K⁻¹

    C. m

    D. mK⁻¹

47. Which of the following is NOT an effect of heat?A. Thermionic emissionB. Change of state

    C. Decrease in volume when cooled

    D. Increase in mass

48. The kinetic theory assumes that in solids, moleculesA. are stationaryB. move freely with high speed

    C. vibrate about fixed mean positions

    D. have no inter-molecular forces

49. A substance that undergoes sublimation changes directly fromA. solid to liquidB. solid to gas

    C. liquid to gas

    D. gas to liquid

50. The strength of inter-molecular forces in a substance determines itsA. colourB. mass

    C. thermal expansivity

    D. atomic number

Answer Key

1. B
2. C
3. B
4. C
5. B
6. C
7. C
8. C
9. B
10. B
11. C
12. B
13. C
14. C
15. B
16. C
17. B
18. C
19. C
20. B
21. B
22. C
23. C
24. C
25. C
26. C
27. B
28. B
29. B
30. B
31. C
32. C
33. B
34. B
35. B
36. A
37. B
38. B
39. C
40. C
41. D
42. C
43. C
44. B
45. C
46. B
47. D
48. C
49. B
50. C

Explanations to Key Questions

Q1: Heat energy is the total internal energy of a body due to the random motion of its molecules. It is not the degree of hotness (that’s temperature) nor a measure of average kinetic energy (that’s temperature). So B is correct.

Q7: Temperature determines the direction of heat flow: heat flows from a region of higher temperature to one of lower temperature. Answer C.

Q8: Effects of heat include change in temperature, change of state, expansion, change in physical properties, thermionic emission, chemical change, and pressure change. Decrease in mass is not an effect of heat; mass remains constant. C is not an effect.

Q9: Solid to liquid is melting. B.

Q15: Liquids have a definite volume (they take the shape of the container but volume is fixed) but no definite shape. B.

Q17: The temperature of a body is a measure of the average kinetic energy of its molecules. Answer B.

Q19: Heat is total internal energy; temperature is degree of hotness. Heat’s SI unit is Joule, temperature’s is Kelvin. So C is correct.

Q22: When a solid is heated, its molecules gain kinetic energy, vibrate with larger amplitude, and move farther apart, causing expansion. C.

Q23: Thermal expansivity is greatest in gases because intermolecular forces are weakest, allowing more expansion per unit temperature rise. C.

Q26: The degree of expansion per unit size per unit temperature rise is thermal expansivity. C.

Q31: Assumption: collisions are perfectly elastic, so ‘inelastic’ is incorrect. C is the wrong statement.

Q36: Statement A says molecules of ice, water, and water vapour have equal intermolecular distances, which is false (distances increase from solid to liquid to gas). So A is not correct. This matches the passage’s example.

Q40: Assumption: collisions between gas molecules are perfectly elastic. C is correct.

Q46: Linear expansivity unit is per Kelvin (K⁻¹). B.

Q47: Increase in mass is not an effect of heat. D.

Q49: Sublimation is the direct change from solid to gas without passing through the liquid state. B.