The area of the glass of a window of a room is $10 m^{2}$ and thickness 2mm. The outer and inner temperature are $40^{\circ}$ C and $20^{\circ}$ C respectively. Thermal conductivity of glass in MKS system is 0.2. The heat flowing in the room per second will be

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30 joules

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45 joules

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Solution

The correct option is B
$\frac{Q}{t} = \frac{K A (θ_{1} - θ_{2})}{l} = \frac{0.2 \times 10 \times 20}{2 \times 10^{- 3}} = 2 \times 10^{4} J / s e c$

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