# NEET Questions Solved

NEET - 2015

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

(a)31°C

(b)41°C

(c)11°C

(d)21°C

Concept Videos :-

#48 | Introduction to Heat Engine
#49 | Solved Example: 23
#50 | Refrigerator
#52 | Carnot Engine
#53 | Carnot Cycle
#54 | Solved Example: 24
#55 | Solved Example: 25

Concept Questions :-

Heat engine and refrigerator

Key Concept:

Coefficient of performance (β) of a refrigerator is defined as the ratio of quantity of heat removed per cycle  to the work done on the working substance per cycle to remove this heat.

Given, coefficient of performance of a refrigerator β=5

Temperature of surface i.e. inside freezer,

T2=-20°C=-20+273=253K

Temperature of surrounding i.e. heat rejected outsider T1=?

So,β=T2/T1-T2

=>$5=\frac{253}{{T}_{1}-253}$

=>5T1=253/T1-253

=>$5{T}_{1}$
-1265=253 =>

$5{T}_{1}$=$1518{T}_{1}$=$\frac{1518}{5}$=$303.6K$

${T}_{1}=303.6-273=31°C$

Difficulty Level:

• 41%
• 28%
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