Heat Pumps

Q.

The ratio of quantity of heat removed per cycle from the contents of the refrigerator to the energy spent per cycle to remove this heat is called the

1. coefficient of performance

2. efficiency of refrigerator

3. efficiency of heat engine

4. principle of heat engine

Q. Briefly discuss the limitations of first law of thermodynamics.

Q. The efficiency of a heat engine is maximum when:

1. temperature of sink $>$ temperature of source
2. temperature of source $>$ temperature of sink
3. the difference between temperature of source and sink is very high
4. none of these

Q. A refrigerator whose coefficient of performance is $5$, extracts heat from the cooling compartment at the rate of $250\text{J/cycle}$. Find the amount of heat discharged per cycle to the room.

1. $50\text{J}$
2. $250\text{J}$
3. $300\text{J}$
4. $200\text{J}$

Q. A refrigerator freezes water at $0^{\circ }\text{C}$ into $10\text{kg}$ ice at $0^{\circ }\text{C}$ in a time interval of $30\text{min}$. Assuming the room temperature to be ${22}^{\circ }\text{C}$, calculate the minimum amount of power needed to make $10\text{kg}$ of ice.
(Take latent heat for freezing as $80\text{kcal/kg}$)

1. $250\text{W}$
2. $150\text{W}$
3. $100\text{W}$
4. $300\text{W}$