A black body at temperature 127 radiates heat at the rate of 5 cal/cm² s. At a temperature 927, its rate of emission in units of cal/cm² s will be (a) 405 (b) 35 (c) 45 (d) 350

Answer: (a). Stefan's law: E ∝ T⁴ (T in kelvin). T₁ = 400 K, T₂ = 1200 K, so (E₂)/(E₁) = 3⁴ = 81. E₂ = 81 × 5 = 405 cal/cm² s So the answer is (a) 405.

A black body at temperature 127 radiates heat at the rate of 5… | MHT CET 2023 (13 May, Shift 1)

Q78MHT CET 2023 · 13 MAY · SHIFT 1Medium

Thermal Radiation: Black Body, Stefan & Wien

A black body at temperature $127^\circ\text{C}$ radiates heat at the rate of $5\text{ cal/cm}^{2}\text{ s}$ . At a temperature $927^\circ\text{C}$ , its rate of emission in units of $\text{cal/cm}^{2}\text{ s}$ will be

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Answer: (a)

Stefan's law: $E \propto T^4$ (T in kelvin).
$T_1 = 400\text{ K}$ , $T_2 = 1200\text{ K}$ , so $\frac{E_2}{E_1} = 3^4 = 81$ .
$E_2 = 81 \times 5 = 405\text{ cal/cm}^2\text{ s}$
So the answer is (a) 405.

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