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Thermodynamics Class 11 MCQs Questions with Answers
Multiple Choice Type Questions
Question 1.
Internal energy of a perfect gas is
(a) wholly potential energy
(b) wholly kinetic energy
(c) partially K.E. and partially P.E. of the molecules
(d) difference of K.E. and P.E. of the molecules
Answer
Answer: (a) wholly potential energy
Question 2.
In an isothermal process, the internal energy of the system
(a) decreases
(b) increases
(c) does not change
(d) none of the above
Answer
Answer: (c) does not change
Question 3.
Thermodynamics is concerned with the
(a) change of state
(b) measurement of heat
(c) transfer of heat
(d) none of the above
Answer
Answer: (c) transfer of heat
Question 4.
For an adiabatic process
(a) temperature changes are bound to occur.
(b) perfect thermal insulation with surroundings are required.
(c) process should be quick.
(d) all of the above are correct.
Answer
Answer: (d) all of the above are correct.
Question 5.
For an isothermal expansion
(a) process should be performed in very small steps.
(b) perfect conducting communication with the surroudings is required.
(c) process should be slow.
(d) all of the above are correct.
Answer
Answer: (d) all of the above are correct.
Question 6.
The efficiency of a Carnot’s engine is
(a) \(\frac {T_2-T_1}{T_2}\)
(b) \(\frac {T_1-T_2}{T_1}\)
(c) \(\frac {T_2}{T_2-T_1}\)
(d) \(\frac {T_1}{T_1-T_2}\)
Answer
Answer: (b) \(\frac {T_1-T_2}{T_1}\)
Question 7.
In a Carnot’s engine, at the end point of the cycle, the temperature is
(a) less than the initial temperature.
(b) more than the initial temperature.
(c) equal to the initial temperature.
(d) zero.
Answer
Answer: (c) equal to the initial temperature.
Question 8.
The first law of thermodynamics is represented as
(a) dQ = dU + dW
(b) dQ = 2dU + dW
(c) dQ = dU – dW
(d) dQ = dU + 2dW
Answer
Answer: (a) dQ = dU + dW
Question 9.
The efficiency of a Carnot’s engine is
(a) η = 1 – \(\frac {Q_2}{Q_1}\)
(b) η = 1 + \(\frac {Q_2}{Q_1}\)
(a) η = 1 – \(\frac {Q_1}{Q_2}\)
(d) η = 1 – \(\frac {Q_1}{Q_2}\)
Answer
Answer: (a) η = 1 – \(\frac {Q_2}{Q_1}\)
Question 10.
The efficiency of a Carnot engine working between 227°C and 27°C is
(a) 100%
(a) 50%
(c) 40%
(a) 20%
Answer
Answer: (c) 40%
Question 11.
Tell which of the following phenomenon are reversible?
(a) Water fall.
(b) Charging of a battery.
(c) Rusting of iron by chemical change.
(d) Production of heat by rubbing of hands.
Answer
Answer: (b) Charging of a battery.
Question 12.
When steam is converted into water, internal energy of the system
(a) increases
(b) decreases
(e) remains constant
(d) becomes zero
Answer
Answer: (b) decreases
Question 13.
The efficiency of a practical engine is
(a) more than the efficiency of Carnot’s engine.
(b) less than the efficiency of Carnot’s engine.
(c) equal to the efficiency of the Carnot’s engine.
(d) none of the above.
Answer
Answer: (b) less than the efficiency of Carnot’s engine.
Question 14.
Sometimes a cycle with well inflated tyres left in the Sun has its tube burst open. This is because the
(a) pressure of air inside the tube increases.
(b) volume of air inside the tube increases.
(c) both volume and pressure of air increases.
(d) none of the above.
Answer
Answer: (a) pressure of air inside the tube increases.
Question 15.
In a heat reservoir, when a certain amount of heat is withdrawn from it, its temperature :
(a) increases
(b) decreases
(c) remains constant
(d) becomes zero
Answer
Answer: (c) remains constant
Question 16.
For an adiabatic process
(a) T1V1γ-1 = T2V2γ-1
(b) T1V11-γ = T2V21-γ
(c) T1V1 = T2V2
(d) T1V2 = T2V1
Answer
Answer: (a) T1V1γ-1 = T2V2γ-1
Question 17.
The temperature of a gas is due to the
(a) K.E. of the gas molecules.
(b) repulsive force between the molecules.
(c) attractive force between the molecules.
(d) P.E. of the gas molecules.
Answer
Answer: (a) K.E. of the gas molecules.
Question 18.
The freezer in a refrigerator is located in the top section so that:
(a) motor is not heated.
(b) heat gained from the environment is more.
(c) heat gained from the environment is less.
(d) the entire chamber of the refrigerator is cooled quickly.
Answer
Answer: (d) the entire chamber of the refrigerator is cooled quickly.
Question 19.
The process forbidden by the first law of thermodynamics is
(a) conversion of w ork into heat.
(b) conversion of heat into work.
(c) change in internal energy.
(d) none of the above.
Answer
Answer: (d) none of the above.
Question 20.
The specific heat at constant pressure is more than that at constant volume due to the fact that:
(a) molecular oscillations are more violent at constant pressure.
(b) additional work need to be done for allowing expansion of gas at constant pressure.
(c) there is more intermolecular attraction at constant pressure.
(d) there is some reason other than those given above.
Answer
Answer: (b) additional work need to be done for allowing expansion of gas at constant pressure.
Fill in the blanks
Question 1.
Change in internal energy is ……………….. for a cyclic process.
Answer
Answer: zero
Question 2.
Internal energy is a ……………….. variable.
Answer
Answer: state
Question 3.
When a drop of water falls on a very hot iron, it at once forms a thin layer of water vapour between the surface and water drop and acts as an ……………….. so permits the water drop to stay for a ………………..
Answer
Answer: insulating layer, longer period.
Question 4.
Temperature changes during ………………..
Answer
Answer: an adiabatic process
Question 5.
The internal energy does not change during an ………………..
Answer
Answer: isothermal process.
Question 6.
Heat cannot flow itself from a body at a lower temperature to a body at higher temperature is the statement of ………………..
Answer
Answer: second law of thermodynamics.
Question 7.
Zeroth law defines ……………….. and first law of thermodynamics defines ………………..
Answer
Answer: temperature, internal energy.
Question 8.
The process in which no heat exchange takes place is called ………………..
Answer
Answer: adiabatic process.
Question 9.
The whole work can be converted into ……………….. through friction.
Answer
Answer: heat.
Question 10.
……………….. is a process in which pressure remains constant.
Answer
Answer: Isobaric.
Question 11.
At ……………….. water and water vapours are equally dense.
Answer
Answer: critical temperature or critical point.
Question 12.
……………….. is a process in which volume remains constant.
Answer
Answer: Isochoric.
Question 13.
In ……………….. and ……………….. processes heat can be added to a system without increasing its temperature.
Answer
Answer: melting, boiling.
Question 14.
……………….. is a process in which temperature remains constant.
Answer
Answer: Isothermal.
Question 15.
The specific heat of ……………….. is maximum.
Answer
Answer: water.
Question 16.
……………….. is a device which is used to transfer heat from a system at low temperature to the surroundings at higher temperature.
Answer
Answer: Refrigerator.
Question 17.
A refrigerator is an esample of ………………..
Answer
Answer: heat pump.
Question 18.
……………….. is concerned with the transfer of heat.
Answer
Answer: Thermodynamics
Question 19.
The area under the P-V diagram gives the ……………….. by or on the system.
Answer
Answer: work done.
Question 20.
Q is not a state variable, but ∆Q is clearly proportional to the total mass of the system and hence is ………………..
Answer
Answer: extensive.
Question 21.
S.I. units of heat capacity and specific heat are ……………….. and ……………….. respectively.
Answer
Answer: JK-1, JK-1 mol-1.
True/False Type Questions
1. Mark True/False statements
(a) The equation for adiabatic process if PVγ = constant.
(b) The equation for isothermal process is PV = constant.
(c) TVγ-1 = constant represents an adiabatic process.
Answer
Answer:
(a) True
(b) True
(c) True
2. Mark True/False statements
(a) Charging of a battery is a reversible process.
(b) Water fall is an irreversible process.
(c) The efficiency of a Carnot engiine working between 227°C and 27°C is 20%.
Answer
Answer:
(a) True
(b) True
(c) False
3. Mark True/False statements
(a) Extensive variables indicate the size of the system while intensive variables do not.
(b) Internal energy, volume, mass are extensive variables while pressure, temperature and density are intensive variables.
(c) The product of an intensive and an extensive variable is equal to an extensive variable [e.g. P∆V + ∆U = ∆Q].
Answer
Answer:
(a) True
(b) True
(c) True
4. Mark True/False statements
(a) ∆U = 0 for a cyclic process.
(b) The system returns to its initial state in a cyclic process.
(c) The total heat absorbed equals the work done by the system.
Answer
Answer:
(a) True
(b) True
(c) True
5. Mark True/False statements
(a) Temperature remains constant for an adiabatic process.
(b) Temperature changes during an isothermal process.
(c) Internal energy of the system decreases during an isothermal process.
Answer
Answer:
(a) False
(b) False
(c) False
6. Mark the True/False statements
(a) The internal energy of a perfect gas is the sum of K.E. and P.E. of the molecules.
(b) The first law of thermodynamics is based on the law of conservation of energy.
(c) Thermodynamics is concerned with the change of state.
Answer
Answer:
(a) False
(b) True
(c) False
7. Select True/False statements
(a) No heat is removed or added to the sy stem in an adiabatic process.
(b) 100% conversion of heat into work is possible.
(c) Absolute zero temperature is also a temperature of zero energy.
Answer
Answer:
(a) True
(b) False
(c) False
8. Select True/False statements
(a) The change in internal energy of the gas and the work done by it are equal in magnitude in an adiabatic process for an ideal gas.
(b) For an ideal gas, the internal energy does not change in an isothermal process.
(c) A gas can be liquified by pressure only when its temperature is lower than its critical temperature.
Answer
Answer:
(a) True
(b) True
(c) True
9. Select True/False statements
(a) β = \(\frac {22}{7}\)
(b) η = \(\frac {Q_1-Q_2}{Q_1}\) = \(\frac {T_1-T_2}{T_1}\)
(c) Mechanical equivalent of heat is defined as the amount of work needed to produce 1 calorie of heat.
Answer
Answer:
(a) True
(b) True
(c) True.
10. Select True/False statements
(a) Volume remains constant in an isochoric process.
(b) Pressure remains constant in an isobaric process.
(c) In S.I. units, the specific heat capacity of water is 4186 J kg-1 K-1 Le. 4.186 J g-1 K-1.
Answer
Answer:
(a) True
(b) True
(c) True
Match Type Questions
| Column I | Column II |
| (a) If thermodynamic variables of the system change with the | (i) Equation of state |
| (b) A relation between pressure, volume and temperature for a system | (ii) Work done by or on a system |
| (c) Area under P-V diagram | (iii) Thermodynamic process |
Answer
Answer:
| Column I | Column II |
| (a) If thermodynamic variables of the system change with the | (iii) Thermodynamic process |
| (b) A relation between pressure, volume and temperature for a system | (i) Equation of state |
| (c) Area under P-V diagram | (ii) Work done by or on a system |
| Column I | Column II |
| (a) Pressure remains constant | (i) Isothermal |
| (b) Temperature remains constant | (ii) Isochoric |
| (c) Volume remains constant | (iii) Isobaric |
Answer
Answer:
| Column I | Column II |
| (a) Pressure remains constant | (iii) Isobaric |
| (b) Temperature remains constant | (i) Isothermal |
| (c) Volume remains constant | (ii) Isochoric |
| Column I | Column II |
| (a) Work done on the system | (i) positive |
| (b) Work done by the system | (ii) negative |
Answer
Answer:
| Column I | Column II |
| (a) Work done on the system | (ii) negative |
| (b) Work done by the system | (i) positive |
| Column I | Column II |
| (a) The gas will get heated i.e. its internal energy will increase if | (i) it expands adiabatically |
| (b) The gas will cool down i.e. its internal energy will decrease if | (ii) it is compressed adiabatically |
Answer
Answer:
| Column I | Column II |
| (a) The gas will get heated i.e. its internal energy will increase if | (ii) it is compressed adiabatically |
| (b) The gas will cool down i.e. its internal energy will decrease if | (i) it expands adiabatically |
| Column I | Column II |
| (a) Heat is supplied to a system but the system does not perform any external work | (i) increases |
| (b) Work done during hammering gets converted into heat energy, so internal energy | (ii) isochoric change |
Answer
Answer:
| Column I | Column II |
| (a) Heat is supplied to a system but the system does not perform any external work | (i) increases |
| (b) Work done during hammering gets converted into heat energy, so internal energy | (ii) isochoric change |
| Column I | Column II |
| (a) Coefficient of performance of a refrigerator decreases as the temperature inside it | (i) decreases |
| (b) Infinite thermal capacity of source and sink | (ii) efficiency of Carnot’s engine |
| (c) Independent of the nature of the working substance | (iii) An ideal heat engine |
Answer
Answer:
| Column I | Column II |
| (a) Coefficient of performance of a refrigerator decreases as the temperature inside it | (i) decreases |
| (b) Infinite thermal capacity of source and sink | (iii) An ideal heat engine |
| (c) Independent of the nature of the working substance | (ii) efficiency of Carnot’s engine |
| Column I | Column II |
| (a) Internal energy of gas is only kinetic in nature | (i) real gas |
| (b) Internal energy of a gas is the sum of K.E. and P.E. | (ii) ideal gas |
Answer
Answer:
| Column I | Column II |
| (a) Internal energy of gas is only kinetic in nature | (ii) ideal gas |
| (b) Internal energy of a gas is the sum of K.E. and P.E. | (i) real gas |
| Column I | Column II |
| (a) ∆U of a system over one complete cycle of a cyclic process | (i) area of the cyclic process |
| (b) Amount of work done in a cyclic process | (ii) zero |
Answer
Answer:
| Column I | Column II |
| (a) ∆U of a system over one complete cycle of a cyclic process | (ii) zero |
| (b) Amount of work done in a cyclic process | (i) area of the cyclic process |
| Column I | Column II |
| (a) Rusting of iron | (i) reversible process |
| (b) Charging of a battery | (ii) irreversible process |
Answer
Answer:
| Column I | Column II |
| (a) Rusting of iron | (ii) irreversible process |
| (b) Charging of a battery | (i) reversible process |
| Column I | Column II |
| (a) Relation between Cp and Cv for one mole of a gas | (i) Cp – Cv = \(\frac {r}{J}\) |
| (b) Relation between Cp and Cv for 1 gram of a gas | (ii) Cp – Cv = R |
| (c) Work done during iso-thermal process | (iii) RT loge \(\frac {v_2}{v_1}\) |
| (d) Work done during an adiabatic process | (iv) \(\frac {R(T_1-T_2)}{ γ-1}\) |
Answer
Answer:
| Column I | Column II |
| (a) Relation between Cp and Cv for one mole of a gas | (ii) Cp – Cv = R |
| (b) Relation between Cp and Cv for 1 gram of a gas | (i) Cp – Cv = \(\frac {r}{J}\) |
| (c) Work done during iso-thermal process | (iii) RT loge \(\frac {v_2}{v_1}\) |
| (d) Work done during an adiabatic process | (iv) \(\frac {R(T_1-T_2)}{ γ-1}\) |
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