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
Medium
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(c) $Q = A\varepsilon \sigma {T^4}$
==> $Q \propto A \propto {r^2}$ ( $\because T =$ constant)
$ \Rightarrow \frac{{{Q_1}}}{{{Q_2}}} = \frac{{r_1^2}}{{r_2^2}} = {\left( {\frac{1}{2}} \right)^2} = \frac{1}{4}$
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