Light with an enargy flux of `25xx10^(4) Wm^(-2)` falls on a perfectly reflecting surface at normal incidence. If the surface area is `15 cm^(2)`, the average force exerted on the surface is

Options

A. `1.25 xx 10^(-6) N`
B. `2.50 xx 10^(-6) N`
C. `1.20 xx 10^(-6) N`
D. `3.0 xx 10^(-6) N`

Answer

C

Explanation

Given S is the rate o f energy transferred per unit time and per unit area . Average force exerted on surface after absorption :
` F_(av ) =(S xx A )/( c ) = ( 25xx10^4 xx 15 xx 10^(-4) )/( 3xx 10^8 ) = 1.25 xx 10^(-6) N`