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baherus [9]
3 years ago
15

A refrigerator is removing heat from a cold medium at 3∘C at a rate of 5400 kJ/h and rejecting the waste heat to a medium at 30∘

C. If the coefficient of performance of the refrigerator is 2, the power consumed by the refrigerator is
(a) 0.5 kW
(b) 0.75 kW
(c) 1.0 kW
(d) 1.5 kW
(e) 3.0 kW
Physics
1 answer:
ipn [44]3 years ago
3 0

Answer:(b) 0.75 kW

Explanation:

Given

temperature of cold region T_L=3^{\circ}C

Heat removal at the rate of Q_1=5400 kJ/h

temperature of hot region T_H=30^{\circ}C

COP of refrigerator =2

COP of a refrigerator is given by ratio of desired effect to the Power input

COP=\frac{Q_1}{Power}

2=\frac{5400}{P}

P=2700 kJ/h

P=0.75 kW

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Answer:

t=14.678\times 10^{-3}s

Explanation:

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C\times 0.9E=CE(1-e^{-\frac{t}{75\times 10^6\ \times\ 85\times 10^{-12}}})

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0.9=1-e^{-\frac{t}{75\times 10^6\ \times\ 85\times 10^{-12}}}

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-\frac{t}{75\times 10^6\ \times\ 85\times 10^{-12}}=-ln(10)

or

t=75\times 10^6\ \times\ 85\times 10^{-12}\times ln{10}

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