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. \(11\%\)

A refrigerator is to maintain eatables kept inside at \(9^\circ \text{C}.\) If room temperature is \(36^\circ \text{C},\) the coefficient of performance is:
1. \(9.3\)
2. \(12.4\)
3. \(11.2\)
4. \(10.4\)

Consider a heat engine as shown in the figure. ${\mathrm{Q}}_1 \mathrm{and} {\mathrm{Q}}_2$ 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:

$(a) {\mathrm{Q}}_1>{\mathrm{Q}}_2>0(b) {\mathrm{Q}}_2>{\mathrm{Q}}_1>0(c) {\mathrm{Q}}_2<{\mathrm{Q}}_1<0(d) {\mathrm{Q}}_1<0, {\mathrm{Q}}_2>0$

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

2. (a, d)

3. (b, d)

4. (a, c)

The efficiency of a Carnot engine depends upon:

1. the temperature of the sink only.

2. the temperatures of the source and the sink.

3. the volume of the cylinder of the engine.

4. the temperature of the source only.

A refrigerator whose coefficient of performance is 5 extracts heat from the cooling chamber at a rate of 250 J per cycle. For refrigeration, the work done per cycle is:

1. 150 J

2. 200 J

3. 100 J

4. 50 J

If a refrigerator extracts heat 'a' from the cold reservoir and 'b' is the heat released from the hot reservoir, then the work done on the refrigerant (system) is:

1. a + b

2. $\mathrm{a}-\mathrm{b}$

3. a

4. $\mathrm{b}-\mathrm{a}$

The coefficient of performance of an ideal refrigerator is 3 which extracts heat from the sink at the rate of 399 J per cycle. The amount of heat it gives to the room per cycle will be:

1 532 J

2 250 J

3 300 J

4 496 J

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

An ideal refrigerator has a freezer at a temperature of –13°C . The coefficient of performance of the engine is 5. The temperature of the air (at which heat is rejected) will be 
1. 325°C
2. 325K
3. 39°C
4. 320°C