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Chapter 21: Q. 20 (page 595)

What are (a) the heat extracted from the cold reservoir and (b) the coefficient of performance for the refrigerator shown in Figure Ex-21.20?

Short Answer

Expert verified

(a)The heat extracted from the cold reservoir, 64J,

(b)The coefficient of performance for the refridgerator1.56

Step by step solution

01

Step: 1 Finding the value of workdone: (part a)

Net work done by the gas can be calculated as follows. This is the energy which is required to be served by external electrical power .

Electrical power used up = 119 J - 78 J = 41 J .

105 J is the total heat given out to the environment . This heat will be the sum of heat extracted and electrical energy used.

We can calculate the heat extracted as follows.

Qc=Qh鈭�W

Qc=105鈭�41=64J

02

Step: 2 Finding the value of K: (part b)

The thermal efficiency is the ratio of the amount of heat extracted from a cold reservoir to the electrical energy required to extract it.. That is,

K=QcW

K=6441=1.56

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