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What is the net amount of energy per unit time being received by a body having a temperature of 40 °C in a surrounding of 60°C? (The surface area of body = 2m^2, σ = 5.67*10^-8W/ m^2K^4 & emissivity of 0.4).

(a) 122.4W

(b) 0.47W

(c) 33W

(d) 86W

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Correct option is (a) 122.4W

To explain I would say: The body will receive some energy from the surrounding and also lose some to it.

The net energy received will be

= AeσT^4 – AeσTS^4

= 2*0.4*5.67*10^-8(333^4 – 313^4)

= 122.4 W.

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