The coefficient of performance of a refrigerator is \(5.\) If the temperature inside the freezer is \(-20^\circ \text{C},\) the temperature of the surroundings to which it rejects heat is:
1. \(31^\circ \text{C}\)
2. \(41^\circ \text{C}\)
3. \(11^\circ \text{C}\)
4. \(21^\circ \text{C}\)

The temperature inside a refrigerator (reversible process) is t₂^oC and the room temperature is t₁^oC. The amount of heat delivered to the room for each joule of electrical energy consumed, ideally, will be:

1.  $\frac{t_1}{t_1-t_2}$

2.  $\frac{t_1+273}{t_1-t_2}$

3.  $\frac{t_2+273}{t_1+t_2}$

4.  $\frac{t_1+t_2}{t_1+273}$

A Carnot engine, having an efficiency of $\mathrm{\eta }$ = $\frac{1}{10}$ as a heat engine, is used as a refrigerator. If the work done on the system is \(10\) J, the amount of energy absorbed from the reservoir at a lower temperature is:
1. \(100\) J
2. \(99\) J
3. \(90\) J
4. \(1\) J

The efficiency of a Carnot engine is 50% and the temperature of the sink is 500K. If the temperature of the source is kept constant and its efficiency raised to 60%, then the required temperature of the sink will be: 

1. 100 K

2. 600 K

3. 400 K

4. 500 K

The ratio (W/Q) for a Carnot engine is $\frac{1}{6}$. Now the temperature of the sink is reduced by 62ºC, then this ratio becomes twice. Therefore, the initial temperature of the sink and source are, respectively:

1. 33ºC, 67ºC

2. 37ºC, 99ºC

3. 67ºC, 33ºC

4. 97 K, 37 K

A carnot engine having an efficiency of $\frac{1}{10}$th of heat engine, is used as a refrigerator. If then work done on the system is 10 J, the amount of energy absorbed from the reservoir at lower temperature is:

1. 1 J

2. 90 J

3. 99 J

4. 100 J 

Consider a heat engine as shown in the figure. ${\mathrm{Q}}_1<mspace\; width="1em"></mspace>\mathrm{and}<mspace\; width="1em"></mspace>{\mathrm{Q}}_2$ are heat added to ${\mathrm{T}}_1$ and heat taken from ${\mathrm{T}}_2$ respectively, in one cycle of the engine. W is the mechanical work done on the engine.

If W > 0, then possibilities are:

$(a)<mspace\; width="1em"></mspace>{\mathrm{Q}}_1>{\mathrm{Q}}_2>0(b)<mspace\; width="1em"></mspace>{\mathrm{Q}}_2>{\mathrm{Q}}_1>0(c)<mspace\; width="1em"></mspace>{\mathrm{Q}}_2<{\mathrm{Q}}_1<0(d)<mspace\; width="1em"></mspace>{\mathrm{Q}}_1<0,<mspace\; width="1em"></mspace>{\mathrm{Q}}_2>0$

Choose the correct alternatives:
1. (b, c)

2. (a, d)

3. (b, d)

4. (a, c)

A steam engine delivers \(5.4\times 10^8\) J of work per minute and extracts \(3.6\times 10^9\) J of heat per minute from its boiler. The efficiency of the engine is:
1. \(15\%\)
2. \(18\%\)
3. \(13\%\)
4. \(11\%\)