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Kinetic Theory and First Law of Thermodynamics MCQs — Physics

180 multiple-choice questions on Kinetic Theory and First Law of Thermodynamics from Physics, each with the correct answer and, where available, a teacher's explanation. Read through them to revise the chapter, then practise the same questions one by one to test yourself.

1. Temperature is a measure of the:

  1. total internal energy
  2. potential energy only
  3. heat content
  4. average kinetic energy of the particles

Answer: D) average kinetic energy of the particles

Explanation: Not the total. SLO P-11-C-12 · Understanding

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2. A 0.5 kg body of specific heat capacity 900 J kg^-1 K^-1 is warmed by 40 K (no work done). The increase in its internal energy is:

  1. 9000 J
  2. 450 J
  3. 36,000 J
  4. 18,000 J

Answer: D) 18,000 J

Explanation: Delta U = mcDeltatheta = 0.5 900 40 = 18,000 J. SLO P-11-C-12 · Understanding

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3. The average translational kinetic energy of a gas molecule at 600 K is (k = 1.38 10^-23 J/K):

  1. 1.24 10^-20 J
  2. 2.48 10^-20 J
  3. 3.73 10^-20 J
  4. 8.28 10^-21 J

Answer: A) 1.24 10^-20 J

Explanation: barEk = 32kT = 1.5 1.38 10^-23 600 = 1.24 10^-20 J. SLO P-11-C-02 · Understanding

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4. Heat flows naturally from:

  1. a body with more internal energy to one with less, always
  2. a colder body to a hotter body
  3. a larger body to a smaller body
  4. a hotter body to a colder body

Answer: D) a hotter body to a colder body

Explanation: Temperature difference drives heat flow. SLO P-12-C-01 · Knowledge

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5. If both the pressure and absolute temperature of a fixed mass of gas are doubled, its volume:

  1. doubles
  2. halves
  3. quadruples
  4. stays the same

Answer: D) stays the same

Explanation: V propto T/p. SLO P-11-C-03 · Application

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6. Kinetic theory assumes that collisions between gas molecules are:

  1. sticky
  2. perfectly elastic
  3. perfectly inelastic
  4. impossible

Answer: B) perfectly elastic

Explanation: No KE is lost. SLO P-11-C-05 · Understanding

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7. On a p–V diagram, a process going from right to left (volume decreasing) means:

  1. heat is zero
  2. no work is done
  3. work is done on the gas
  4. work is done by the gas

Answer: C) work is done on the gas

Explanation: Compression. SLO P-11-C-07 · Understanding

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8. Pumping up a bicycle tyre makes the pump warm because:

  1. heat flows in from outside
  2. friction only
  3. work is done on the air, raising its internal energy
  4. air does work on the pump

Answer: C) work is done on the air, raising its internal energy

Explanation: Compression heats the gas. SLO P-11-C-07 · Understanding

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9. A gas at 1 10^5 Pa and 290 K occupies 0.024 m^3. The amount of gas is:

  1. 1.99 mol
  2. 9.96 mol
  3. 0.996 mol
  4. 0.498 mol

Answer: C) 0.996 mol

Explanation: n = PVRT = 0.996 mol. SLO P-11-C-03 · Application

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10. A gas absorbs 800 J of heat and has 100 J of work done on it. The change in its internal energy is: (Use Q = Delta U + W, where Q = heat supplied to the gas and W = work done by the gas.)

  1. 1800 J
  2. 900 J
  3. 450 J
  4. 9000 J

Answer: B) 900 J

Explanation: Delta U = Q - W = 800 - (-100) = 900 J. SLO P-11-C-08 · Application

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11. 27 °C on the kelvin scale is:

  1. 300 K
  2. 27 K
  3. 246 K
  4. 327 K

Answer: A) 300 K

Explanation: T = theta + 273. SLO P-11-C-03 · Application

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12. A gas loses 200 J of heat and has 50 J of work done on it. The change in its internal energy is: (Use Q = Delta U + W, where Q = heat supplied to the gas and W = work done by the gas.)

  1. -75 J
  2. -300 J
  3. -150 J
  4. -1500 J

Answer: C) -150 J

Explanation: Delta U = Q - W = -200 - (-50) = -150 J. SLO P-11-C-08 · Application

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13. Work done by a gas is positive when:

  1. the gas is cooled at constant volume
  2. the volume stays constant
  3. the gas expands
  4. the gas is compressed

Answer: C) the gas expands

Explanation: Wby = pDelta V, Delta V 0. SLO P-11-C-07 · Understanding

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14. In pV = nRT, the temperature must be in:

  1. degrees Celsius
  2. any unit
  3. degrees Fahrenheit
  4. kelvin

Answer: D) kelvin

Explanation: The ideal gas law uses absolute temperature. SLO P-11-C-03 · Application

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15. The gradient of a p against 1V line equals:

  1. 1nRT
  2. nRT
  3. nRT
  4. RT/n

Answer: C) nRT

Explanation: p = nRT 1V. SLO P-11-C-10 · Application

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16. If the work done by a gas is +300 J, the work done on the gas is:

  1. 0 J
  2. +300 J
  3. -300 J
  4. 600 J

Answer: C) -300 J

Explanation: They are equal and opposite. SLO P-11-C-07 · Understanding

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17. Regions at equal temperature:

  1. always have equal internal energy
  2. have no net transfer of thermal energy between them
  3. always have equal heat capacity
  4. are always at 0 °C

Answer: B) have no net transfer of thermal energy between them

Explanation: Definition of thermal equilibrium. SLO P-12-C-01 · Knowledge

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18. A gas at constant pressure 1.5 10^5 Pa changes volume from 0.004 m^3 to 0.001 m^3. The work done by the gas is:

  1. -45 J
  2. -450 J
  3. 450 J
  4. -4500 J

Answer: B) -450 J

Explanation: W = pDelta V = 1.5 10^5 (0.001 - 0.004) = -450 J. (Negative: the gas is compressed, so work is done on it.) SLO P-11-C-06 · Application

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19. The internal energy of a solid is made up of:

  1. only nuclear energy
  2. the kinetic energy of vibrating atoms and the potential energy of their bonds
  3. only gravitational energy
  4. only the solid's motion as a whole

Answer: B) the kinetic energy of vibrating atoms and the potential energy of their bonds

Explanation: Two components. SLO P-11-C-12 · Understanding

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20. One assumption of the kinetic theory of an ideal gas is that the molecules:

  1. are at rest
  2. attract each other strongly
  3. have negligible volume compared with the container
  4. occupy most of the container

Answer: C) have negligible volume compared with the container

Explanation: They are treated as points. SLO P-11-C-05 · Understanding

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21. A gas does 250 J of work in a cycle. The net heat it absorbs in the cycle is:

  1. 0 J
  2. 250 J
  3. 500 J
  4. -250 J

Answer: B) 250 J

Explanation: Delta U = 0 for a cycle. SLO P-11-C-11 · Application

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22. For a change at constant volume (isochoric):

  1. Q = 0
  2. Delta U = 0
  3. W = 0, Q = Delta U
  4. Q = -W

Answer: C) W = 0, Q = Delta U

Explanation: No volume change, so no work. SLO P-11-C-08 · Application

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23. A gas is compressed by 300 J of work and gives out 300 J of heat. Its internal energy:

  1. does not change
  2. falls by 300 J
  3. rises by 600 J
  4. rises by 300 J

Answer: A) does not change

Explanation: Delta U = Q - W = -300 - (-300) = 0. SLO P-11-C-11 · Application

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24. At constant temperature, the average speed of gas molecules:

  1. stays the same
  2. is zero
  3. decreases with pressure
  4. increases with pressure

Answer: A) stays the same

Explanation: Speed depends on T only. SLO P-11-C-09 · Understanding

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25. When a gas expands against a piston, work is done:

  1. by nobody
  2. by the gas on the surroundings
  3. on the gas by the surroundings
  4. only on the container walls

Answer: B) by the gas on the surroundings

Explanation: The gas pushes the piston out. SLO P-11-C-07 · Understanding

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