The coefficient of performance of a refrigerator is 5. If the temperature inside freezer is - 20°C, the temperature of the surroundings to which it rejects heat is:

  • Option 1)

    41°C

  • Option 2)

    11°C

  • Option 3)

    21°C

  • Option 4)

    31°C

 

Answers (1)

As we learnt in

Coefficient of performance (beta) -

eta = frac{Q_{2}}{Q_{1}-Q_{2}}= frac{T_{2}}{T_{1}-T_{2}}T_{2}=-20^{\circ}C=253K
 

- wherein

T_{1}> T_{2}

For a perfect refrigerator eta 
ightarrow infty

 

 Coefficient of performance of a refrigerator is

\beta = \frac{T_{2}}{T_{1}-T_{2}}\ \: \: \: \: \: .........(1)

T_{2}=-20^{\circ}C=253K

B = 5

From equation (1)

 5=\frac{253}{T_{1}-253}

or     5T_{1}-1265=253

or     5T_{1}=1518

T_{1}=303.6K=30.6^{\circ}C

Correct option is 4.

 

 

 


Option 1)

41°C

This option is incorrect.

Option 2)

11°C

This option is incorrect.

Option 3)

21°C

This option is incorrect.

Option 4)

31°C

This option is correct.

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