A black disc has a radius 'R' and wavelength corresponding to the maximum intensity is ' λ '. The emissive power (E) for the different radii and maximum wavelengths is directly proportional to (a) R, λ (b) R², λ⁻⁴ (c) R², λ⁻² (d) R², λ

Answer: (b). Power from the disc: E = σ A T⁴ with A ∝ R². Wien: T = (b)/(λ) ⇒ T⁴ ∝ λ⁻⁴. E ∝ R² λ⁻⁴, so the answer is (b).

A black disc has a radius 'R' and wavelength corresponding to the… | MHT CET 2026 (15 Apr, Shift 1)

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Thermal Radiation: Black Body, Stefan & Wien

A black disc has a radius 'R' and wavelength corresponding to the maximum intensity is ' $\lambda$ '. The emissive power (E) for the different radii and maximum wavelengths is directly proportional to

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Answer: (b)

Power from the disc: $E = \sigma A T^4$ with $A \propto R^2$ .
Wien: $T = \frac{b}{\lambda} \Rightarrow T^4 \propto \lambda^{-4}$ .
$E \propto R^2 \lambda^{-4}$ , so the answer is (b).

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