What is the force exerted by a photon beam of intensity `1.4kW//m^(2)`, if it falls on a perfectly absorbing disc of radius 4 metre ?

Options

A. `8.35xx10^(4)N`
B. `10^(8)N`
C. `8.8xx10^(-8)N`
D. `2.35xx10^(-4)`N

Answer

D

Explanation

The pressure exerted by a photon beam when it falls on a perfectly absorbing surface is `P=I/C`
`:.F=PxxA=I/C xx pi r^(2)`
`=(1.4xx10^(3))/(3xx10^(8))xx(3.142)xx16`
`=(16xx1.4xx3.142)/(3)xx10^(-5)`
`=23.46xx10^(-5)=2.35xx10^(-4)N`