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  • A refrigerator freezes 1 kg of water at in 3 minutes. The room temperat

A refrigerator freezes 1 kg of water at 0^{\circ} \mathrm{C} in 3 minutes. The room temperature is 27^{\circ} \mathrm{C} The latest heat of fusion of ice is 80 cal/g then choose the incorrect statement

Option: 1

\mathrm{\text { Heat extracted from water is } 3.36 \times 10^5 \mathrm{~J}}


Option: 2

The coefficient of performance is nearly equal to 10


Option: 3

\mathrm{\text { The work done by the motor is nearly } 3.36 \times 10^4 \mathrm{~J}}


Option: 4

The power of the momter is nearly 30 kW


Answers (1)

\mathrm{\text { (a)Heat extracted from water is } Q_2=m L=10^3 \times 80=80,000 \mathrm{~J}=80,000 \times 4.2=3.36 \times 10^5 \mathrm{~J} \text {. So choice (a) is correct }}

\mathrm{\text { (b) } \beta=\frac{T_2}{T_1-T_2}=\frac{273}{300-273} \simeq 10 \text {. Choice (b) is correct }}

\mathrm{\text { (c) } W=\frac{Q_2}{\beta}=\frac{3.36 \times 10^5}{10} \simeq 3.36 \times 10^4 \mathrm{~J} \text {, which is choice (c) }}

\mathrm{\begin{aligned} & \text { (d) } Q_1=Q_2+W=3.36 \times 10^5+3.36 \times 10^4 \\ & \simeq 37 \times 10^4 \mathrm{~J} \end{aligned}}

\mathrm{\text { Power }=\frac{Q_1}{t}=\frac{37 \times 10^4 \mathrm{~J}}{180 \mathrm{~s}} \simeq 20 \mathrm{~kW} \text {. So choice (d) is incorrect }}

Posted by

Sumit Saini

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