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NEET 2018 · Thermal Radiation: Black Body, Stefan & Wien

Thermal Radiation: Black Body, Stefan & Wien question from NEET 2018

Q100NEET 2018Medium

Thermal Radiation: Black Body, Stefan & Wien

The power radiated by a black body is P and it radiates maximum energy at wavelength, $\lambda$ 0. If the temperature of the black body is now changed so that it radiates maximum energy at wavelength $\frac{3}{4}\lambda_0$ , the power radiated by it becomes nP. The value of n is

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Answer: (c)

Wien's law: $T \propto \frac{1}{\lambda_m}$ , so $\lambda_m' = \frac{3}{4}\lambda_0 \Rightarrow T' = \frac{4}{3}T$ .
Power $P \propto T^4 \Rightarrow nP = \left(\frac{4}{3}\right)^4 P$
$n = \frac{256}{81}$
So the answer is (c) $\frac{256}{81}$ .

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