Heat Pumps

Q. The temperature inside a refrigerator is $t_2^{}°C$ and the room temperature is $t_1^{}°C$. The amount of heat delivered to the room for each joule of electrical energy consumed ideally will be

1. $\frac{t_2+273}{t_1-t_2}$
2. $\frac{t_1+t_2}{t_1+273}$
3. $\frac{t_1}{t_1-t_2}$
4. $\frac{t_1+273}{t_1-t_2}$

Q.

When the door of a refrigerator is kept open, then the room temperature starts

OPTIONS​

a) cool down

b) hot up

[Dear mentor please give the detailed solution]

Q.

What are the applications of the second law of thermodynamics?

Q. The coefficient of performance of a refrigerator is $5$ . If the temperarture inside freezer is $-{20}^0$C, the temperature of the surroundings to which it rejects heat is

1. $21°C$
2. $31°C$
3. $41°C$
4. $11°C$

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. An ideal refrigerator has a freezer at a temperature of $-{13}^{\circ }\text{C}$. The coefficient of performance of the engine used is $5$. The temperature of the air (to which heat is rejected) will be

1. ${325}^{\circ }\text{C}$
2. $325\text{K}$
3. ${39}^{\circ }\text{C}$
4. ${320}^{\circ }\text{C}$

Q.

What is the entropy of the Universe?

Q.

The temperature dropped $15$ degree celsius in the last $30$ days. If the rate of temperature drop remains the same, how many degrees will the temperature drop in the next ten days?

Q.

What are the two laws of thermodynamics?

Q. The efficiency of a Carnot heat engine is $\frac{1}{3}.$ Find the coefficient of performance of Carnot refrigerator when both heat engine and refrigerator are working between similar source and sink.

1. $4$
2. $2$
3. $7.1$
4. $3.25$

Q. A solid body of constant heat capacity
1 $J{/}^{\circ }C$ is being heated by keeping it in contact with reservoirs in two ways.
(i) Sequentially keeping in contact with 2 reservoirs such that each reservoir supplies same amount of heat.
(ii) Sequentially keeping in contact with 8 reservoirs such that each reservoir supplies same amount of heat.
In both cases, the body is brought from initial temperature ${100}^{\circ }C$ to final temperature ${200}^{\circ }C$. Entropy change of the body in two cases respectively is

1. $ln2,2ln2$
2. $ln2$, $ln2$
3. $ln2,4ln2$
4. $ln2,8ln2$

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. $300\text{W}$

Q. Considering an ideal refrigerator, heat from its inside at a temperature of $277\text{K}$ is transferred to a room at temperature of $300\text{K}$. Find the amount of heat extracted for each Joule of electrical energy consumed by refrigerator.

1. $1\text{J}$
2. $12\text{J}$
3. $15\text{J}$
4. $1.3\text{J}$

Q. A Carnot refrigerator $A$ works between $-{10}^{\circ }\text{C}$ and ${27}^{\circ }\text{C}$, while Carnot refrigerator $B$ works between $-{27}^{\circ }\text{C}$ and ${17}^{\circ }\text{C}$, both removing heat equal to $200\text{J}$ from the freezer. Then which of the following is the correct option regarding the coefficient of performance $\left(\beta \right)$ of both the refrigerators?

1. ${\beta }_A<{\beta }_B$
2. ${\beta }_A>{\beta }_B$
3. ${\beta }_A={\beta }_B=0$
4. ${\beta }_A={\beta }_B\ne 0$

Q. A domestic refrigerator is working between the melting ice temperature and the atmosphere at ${17}^{\circ }\text{C}$. The energy which must be supplied to freeze one $\text{kg}$ of water already at $0^{\circ }\text{C}$ is
(Assume the laent heat for freezing be $80\text{kcal}$)

1. $2.092\times {10}^4\text{J}$
2. $3.064\times {10}^4\text{J}$
3. $2.092\times {10}^6\text{J}$
4. $3.064\times {10}^6\text{J}$

Q. Which of the following diagram correctly represents the working of a Carnot's refrigerator?

1. 
2. 
3. 
4. 

Q. A refrigerator absorbs 2000 cals of heat from ice trays. If the coefficient of performance is 4, then work done by the motor is

1. 500 J
2. 2100 J
3. 4200 J
4. 8400 J

Q.

What are the two factors of thermal efficiency?

Q.

Practical unit of power are

1. KW

2. MW

3. GW

4. $hp$

Q.

The second law of thermodynamics can be given as __________.

Q. When the door of a refrigerator is kept open then the room temperature starts

1. cool down
2. hot up
3. first cool down then hot up
4. neither cool down nor hot up

Q. You must have seen that water vapour starts to condense in an air conditioner. Why?

1. The AC is leaking, call a mechanic.
2. The temperature at the AC is lesser than the dew point temperature.
3. It is so hot outside, I don't even wanna be reminded of ACs
4. The temperature at the AC is more than the dew point temperature.

Q.

What is the difference between a heat pump and a central air system?

Q. An ideal refrigerator has a freezer at a temperature of $-{13}^{\circ }\text{C}$. The coefficient of performance of the engine used is $5$. The temperature of the air (to which heat is rejected) will be

1. ${325}^{\circ }\text{C}$
2. $325\text{K}$
3. ${39}^{\circ }\text{C}$
4. ${320}^{\circ }\text{C}$

Q. A refrigerator has to transfer an average of $263J$ of heat per second from temperature $-{10}^{o}C$ to $+{27}^{o}C$. Assuming no other power losses, the average power consumed by the refrigerator in watt is:

1. $300$
2. $263$
3. $187$
4. $35$

Q. Considering an ideal refrigerator, heat from its inside at a temperature of $277\text{K}$ is transferred to a room at temperature of $300\text{K}$. Find the amount of heat extracted for each Joule of electrical energy consumed by refrigerator.

1. $1\text{J}$
2. $1.3\text{J}$
3. $12\text{J}$
4. $15\text{J}$

Q. A carnot cycle is having maximum efficiency because

1. it comprises of two adiabatic process which requires no heat in its execution.
2. its every process is reversible
3. none of the above
4. it comprises of two isothermal process.

Q.

A refrigerator whose coefficient of performance $K=5$, extracts heat from the cooling compartment at the rate of $250J/cycle$. What is the work done per cycle to operate the refrigerator? How much heat is discharged per cycle to the room which acts as the high-temperature reservoir?

Q.

A body cools from 80 °C to 50 °C in 5 minutes. Calculate the time it takes to cool from 60 °C to 30 °C. The temperature of the surroundings is 20 °C.

Q. A refrigerator is a device which works on the principle that evaporation of a liquid gives a cooling effect.

1. True
2. False