Pressure exerted by an electromagnetic wave of intensity I (watts/m^2) on a nonreflecting surf

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8.Electromagnetic waves

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The pressure exerted by an electromagnetic wave of intensity $I (watts/m^2)$ on a nonreflecting surface is [$c$ is the velocity of light]

A

$Ic$

B

$I{c^2}$

C

$I/c$

D

$I/{c^2}$

Solution

(c) Momentum of a photon

$=\frac{h}{\lambda}=\frac{h}{c / v}=\frac{h v}{c}=\frac{E}{c}$

Momentum over unit area

$=\frac{E}{A c}=\frac{I}{c}\left[I=\frac{E}{A} \text { for wave }\right]$

since surface is non reflecting, final momentum of photon $= 0,$ change in momentum $=\frac{I}{c}$

So, force per unit area $=\frac{I}{c}$

Pressure of radiation $=\frac{I}{c}$

Standard 12

Physics

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