Thermodynamics : 100 Most Important Questions with Solutions

1. Zeroth law of thermodynamic defines

1. internal energy
2. enthalpy
3. temperature
4. pressure

Ans. C

Sol. Zeroth law of thermodynamics states about thermal equilibrium of bodies.

2.If a heat engine produces work without the consumption of energy, then what kind of machine is this?

1. Perpetual motion machine of first kind (PMM1)
2. Perpetual motion machine of second kind (PMM2)
3. Perpetual motion machine of third kind (PMM3)
4. None of these

Ans. A

Sol.

• This kind of device is impossible.
•  PMM1 is a hypothetical engine which develops work without receiving the heat energy.

3.The quantity of heat required to change the temperature of 1 gm of ice from -6 °C to -5 °C is known as

1. Latent heat of freezing
2. Freezing heat
3. Heat of vaporization
4. Specific heat

Ans. D

Sol. Specific heat capacity (C) is used for calculations that involve a temperature change, but no phase change. For liquid water, C=4.184 J/(g⋅^∘C).
Since there is no phase change only temperature change so it is specific heat.

4.Which of the following is a closed system?

1. Air conditioned railway coach
2. Biogas digester
3. Sun
4. Fountain pen while writing

Ans. C

Sol.

A closed system is defined when a particular quantity of matter is under study. A closed system always contains the same matter. There can be no mass transfers across the boundary. There may be energy transfer across the boundary. Sun transmits only energy but it doesn’t transmit any mass hence it is a closed system.

5.A house refrigerator with its door open is switched on in a closed room. The air in the room is

1. cooled
2. remains at same temperature
3. heated
4. heated or cooled depending on atmospheric pressure

Ans. C

Sol. In any refrigerator a certain amount of heat Q2 is absorbed from the objects you want to cool and a larger amount of heat Q1 is released to the outside through the radiator behind the refrigerator. If you keep your hand on the radiator, it will feel warm. When the door of the refrigerator is kept open, the compressor will work all the time as the heat in the room is too large and the temperature never reaches the cutoff point of the thermostatic switch. So more heat is released into the room than what is absorbed. If the ventilation is insufficient this will cause the room to warm up.

PDF OF 100 MOST IMPORTANT QUESTIONS OF THERMODYNAMICS 

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