**3.A] State Wein’s law and Rayleigh-Jeans’s law and mention their drawbacks.**

**Answer:-**

## Wien’s distribution law:-

In the year 1893 Wien using thermodynamics showed that the energy emitted per unit volume in the wavelength range \lambda and \lambda+d\lambda.

Equation: E_{\lambda}d\lambda=\frac{C1}{\lambda^{5}}e^{-\frac{C2}{\lambda T}}d\lambda

Here C_{1}=8\Pi hc and C2=\frac{hc}{k} are empirical constants. A suitable selection for these constants helps to explain the experimental curve in the shorter wavelength region.

The drawback of this law is it fails to explain the curve in the longer wavelength region. Also according to this equation the energy density at high temperatures tends to zero which contradicts experimental observations.

## Rayleigh – Jeans law:-

British Physicists Lord Rayleigh and James Jeans made an attempt to explain the Black Body radiation spectrum Based on the concepts formation of standing electromagnetic waves and the law of equipartition of energy. According to this law the energy density of radiation is given by

Equation : E_{\lambda}d\lambda=\frac{8\Pi kT}{\lambda^{4}}d\lambda

Here k is Boltzmann constant with value 1.38\times 10^{-23}JK^{-1} .

This law successfully explains the energy distribution of black body radiation in the longer wavelength region.

According to this law black body is expected to radiate a large amounts of energy in the shorter wavelength region thus leading to no energy available for emission in the longer wavelength region. Experimental observations show that most of the emissions of the black body radiation occur in the visible and infrared regions. This discrepancy is called Ultraviolet Catastrophe.

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