First slide

Quantum Theory of Light

Question

The pressure exerted by an electromagnetic wave of intensity I(W $m^{2}$ ) on a non-reflecting surface is [c is the velocity of light]

Moderate

A

$I / c$
B

${Ic}^{2}$
C

$Ic$
D

$I / c^{2}$

Solution

When a surface intercepts electromagnetic radiation, a force and a pressure are exerted on the surface. As the surface is non-reflecting, so, it is completely absorbed and in such case the force is $F = \frac{IA}{c}$
where 1 is intensity of light' A is area of surface and c is velocity of electromagnetic wave.
The radiation pressure is the force per unit area i.e., $P = \frac{F}{A} = \frac{I}{c}$ .

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