NTS NAT-ICS (Computer Science Track) Physics Heat & Thermodynamics — Set 2

Heat & Thermodynamics MCQs set 2 for NTS NAT-ICS (Computer Science Track) Physics — 20 solved questions.

NTS NAT-ICS (Computer Science Track) Physics Heat & Thermodynamics — Set 2

  1. Question 1

    Q1. The first law of thermodynamics is based on the law of conservation of

    • A) Energy
    • B) Momentum
    • C) Charge
    • D) Mass

    Answer: Energy

    Explanation: The first law, ΔU = Q - W, represents energy conservation, where ΔU is internal energy change, Q is heat added, and W is work done.

  2. Question 2

    Q2. In an adiabatic expansion, the temperature of an ideal gas

    • A) Increases
    • B) Decreases
    • C) Remains constant
    • D) First increases then decreases

    Answer: Decreases

    Explanation: In adiabatic expansion, Q = 0, and W is positive, so ΔU is negative, causing temperature to decrease, as per ΔU = nCvΔT.

  3. Question 3

    Q3. The efficiency of a Carnot engine is 1 / 2. If the sink temperature is 300 K, the source temperature is

    • A) 300 K
    • B) 400 K
    • C) 500 K
    • D) 600 K

    Answer: 600 K

    Explanation: Efficiency = 1 - (T_sink / T_source). Given efficiency = 1 / 2 and T_sink = 300 K, we get 1 / 2 = 1 - (300 / T_source), so T_source = 600 K.

  4. Question 4

    Q4. The specific heat capacity at constant volume (Cv) for an ideal monatomic gas is

    • A) (3 / 2)R
    • B) (5 / 2)R
    • C) (7 / 2)R
    • D) 2R

    Answer: (3 / 2)R

    Explanation: For a monatomic ideal gas, Cv = (3 / 2)R, where R is the gas constant, derived from the kinetic theory of gases.

  5. Question 5

    Q5. In a thermodynamic process, the pressure of a gas is kept constant. The process is

    • A) Isobaric
    • B) Isochoric
    • C) Isothermal
    • D) Adiabatic

    Answer: Isobaric

    Explanation: An isobaric process is one where the pressure remains constant, as per the definition of isobaric processes.

  6. Question 6

    Q6. The change in internal energy of a system is zero when the process is

    • A) Isothermal
    • B) Adiabatic
    • C) Isobaric
    • D) Isochoric

    Answer: Isothermal

    Explanation: For an ideal gas, internal energy (U) depends only on temperature. In an isothermal process, temperature remains constant, so ΔU = 0.

  7. Question 7

    Q7. The molar specific heat of a gas at constant pressure (Cp) is greater than at constant volume (Cv) because

    • A) At constant pressure, the gas expands and does work
    • B) At constant volume, the gas is compressed
    • C) Cp includes the energy required to do work
    • D) Cv is always less than Cp

    Answer: Cp includes the energy required to do work

    Explanation: Cp > Cv because Cp includes the energy required to do work against external pressure, as per Cp = Cv + R.

  8. Question 8

    Q8. For a given amount of an ideal gas, which of the following is true?

    • A) PV = constant at constant T
    • B) P / T = constant at constant V
    • C) V / T = constant at constant P
    • D) All of the above

    Answer: All of the above

    Explanation: Ideal gas law, PV = nRT, implies that at constant T, PV = constant; at constant V, P / T = constant; and at constant P, V / T = constant.

  9. Question 9

    Q9. The temperature of a body is a measure of its

    • A) Total energy
    • B) Internal energy
    • C) Kinetic energy
    • D) Potential energy

    Answer: Internal energy

    Explanation: Temperature is a measure of the average kinetic energy of particles, related to internal energy, not total, kinetic, or potential energy directly.

  10. Question 10

    Q10. The second law of thermodynamics implies that

    • A) Heat always flows from a colder body to a hotter body
    • B) The total entropy of an isolated system always increases
    • C) The efficiency of a heat engine can be 100%
    • D) The internal energy of an ideal gas is a function of pressure

    Answer: The total entropy of an isolated system always increases

    Explanation: The second law states that the total entropy of an isolated system always increases or remains constant, never decreases.

  11. Question 11

    Q11. A thermodynamic system undergoes a cyclic process. The change in internal energy is

    • A) Positive
    • B) Negative
    • C) Zero
    • D) Undefined

    Answer: Zero

    Explanation: In a cyclic process, the system returns to its initial state, so ΔU = 0, as internal energy is a state function.

  12. Question 12

    Q12. The heat capacity of a body is defined as

    • A) The amount of heat required to raise its temperature by 1 K
    • B) The amount of heat required to raise the temperature of 1 kg by 1 K
    • C) The amount of heat required to change its state
    • D) The amount of work done on the body

    Answer: The amount of heat required to raise its temperature by 1 K

    Explanation: Heat capacity is the amount of heat (Q) required to change the temperature (T) of a body by 1 K, given by C = Q / ΔT.

  13. Question 13

    Q13. The ratio of the specific heat capacities (Cp / Cv) for a monatomic ideal gas is

    • A) 5 / 3
    • B) 7 / 5
    • C) 3 / 2
    • D) 4 / 3

    Answer: 5 / 3

    Explanation: For a monatomic ideal gas, Cp = (5 / 2)R and Cv = (3 / 2)R, so Cp / Cv = 5 / 3.

  14. Question 14

    Q14. In an isothermal expansion of an ideal gas, the internal energy

    • A) Increases
    • B) Decreases
    • C) Remains constant
    • D) First increases then decreases

    Answer: Remains constant

    Explanation: For an ideal gas, internal energy (U) depends only on temperature. In an isothermal process, T remains constant, so U remains constant.

  15. Question 15

    Q15. For an ideal gas, the work done in an isothermal expansion from V1 to V2 is given by

    • A) nRT ln(V2/V1)
    • B) nRT ln(V1/V2)
    • C) P(V2 - V1)
    • D) nR(T2 - T1)

    Answer: nRT ln(V2/V1)

    Explanation: Work done in isothermal expansion is given by nRT ln(V2/V1), derived from the ideal gas law and the definition of work.

  16. Question 16

    Q16. A gas is compressed adiabatically. The change in internal energy is

    • A) Zero
    • B) Positive
    • C) Negative
    • D) Depends on the gas

    Answer: Positive

    Explanation: In adiabatic compression, work is done on the gas, increasing its internal energy, so ΔU is positive.

  17. Question 17

    Q17. For a given process, the heat absorbed is 100 J and the work done is 50 J. The change in internal energy is

    • A) 50 J
    • B) 150 J
    • C) 200 J
    • D) -50 J

    Answer: 50 J

    Explanation: ΔU = Q - W = 100 J - 50 J = 50 J, applying the first law of thermodynamics.

  18. Question 18

    Q18. The root mean square speed of the molecules of an ideal gas is proportional to

    • A) √T
    • B) T
    • C) 1/√T
    • D) 1/T

    Answer: √T

    Explanation: v_rms = √(3RT/M), so v_rms ∝ √T, derived from the kinetic theory of gases.

  19. Question 19

    Q19. The specific heat capacity at constant pressure (Cp) for an ideal gas is

    • A) Cv + R
    • B) Cv - R
    • C) R/Cv
    • D) Cv

    Answer: Cv + R

    Explanation: For an ideal gas, Cp - Cv = R, so Cp = Cv + R, a fundamental thermodynamic relation.

  20. Question 20

    Q20. A thermodynamic system undergoes a cycle. The change in internal energy is

    • A) Positive
    • B) Negative
    • C) Zero
    • D) Depends on the cycle

    Answer: Zero

    Explanation: In a cyclic process, the initial and final states are the same, so ΔU = 0.