NEET Physics Thermodynamics Questions Solved

NEET - 2016

A refrigerator works between 4°C and 30°C. It is required to remove 600 calories of heat every second in order to keep the temperature of the refrigerated space constant. The power required is (Take, 1 cal = 4.2 Joules)

(a)23.65W
(b)236.5W
(c)2365W
(d)2.365W

(b) Given temperature of source T=30°C=30+273 T1=303K
Temperature of sink T2=4°C=4+273 T2=277K

As we know that 
Q1/Q2=T1/T2
=>Q2+W/Q2=T1/T2 ..........(W=Q1-Q2)

where Q2 is the amount of heat drawn from the sink (at T2),W is workdone on working substance,
Q1 is amount of heat rejected to source (at room temperature T1).

=>WT2+T2Q2=T1Q2
=>WT2=T1Q2-T2Q2
=>WT2=Q2(T1-T2)
=>W=Q2(T1/T2-1)
=>W=600X4.2X(303/277-1)
W=600X4.2X(26/277)
W=236.5Joules

Power=Workdone/Time=W/t=236.5/1=236.5W

Difficulty Level:

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