A black rectangular surface of area A emits energy E per unit time at 27° C. If length and breadth is reduced to (1/4)th of initial value and temperature is raised to 327° C, then energy emitted per unit time becomes (a) E (b) 2E (c) E/2 (d) E/4

Answer: (a). E ∝ A T⁴. Length and breadth become 1/4: A → A/16. T: 300 K → 600 K, factor 16. E' = 16/16E = E, so the answer is (a).

A black rectangular surface of area A emits energy E per unit time at… | MHT CET 2026 (13 Apr, Shift 1)

Q30MHT CET 2026 · 13 APR · SHIFT 1Medium

Thermal Radiation: Black Body, Stefan & Wien

A black rectangular surface of area A emits energy E per unit time at $27^\circ$ C. If length and breadth is reduced to $\left(\frac{1}{4}\right)^{th}$ of initial value and temperature is raised to $327^\circ$ C, then energy emitted per unit time becomes

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Answer: (a)

$E \propto A T^4$ .
Length and breadth become $\frac{1}{4}$ : $A \to \frac{A}{16}$ .
$T: 300\text{ K} \to 600\text{ K}$ , factor $16$ .
$E' = \frac{16}{16}E = E$ , so the answer is (a).

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