First slide

Radiation

Question

The rate of dissipation of heat by a black body at temperature T is Q. What will be the rate of dissipation of heat by another body at temperature 2T and emissivity 0.25?

Moderate

A

16Q
B

4Q
C

8Q
D

4.5Q

Solution

By Stefan's law
Q = ${σT}^{4}$
The rate of dissipation of heat by a body emissivity e is given be
$Q^{'} = {eσT}^{'} 4$
There $T^{'} = 2 T, e = 0.25$
$∴ Q = 0.25 \times σ {(2 T)}^{4}$
= $4 {σT}^{4} = 4 Q$

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