Question

Two spheres made of same material have radii in the ratio 1 : 2. Both are at same temperature. Ratio of heat radiation energy emitted per second by them is

• A. 1 : 2
• B. 1 : 8
• C. 1 : 4
• D. 1 : 16

Answer 1

Answer: (C)

1 : 4

Answer 2

$P = \frac{Q}{t} = A\sigma T^{4}$ ∴ $\frac{P_{1}}{P_{2}} = \frac{A_{1}}{A_{2}} = \frac{r_{1}^{2}}{r_{2}^{2}} = \left( \frac{1}{2} \right)^{2} = \frac{1}{4}$

[If T = constant]