Question

A plane e.m. wave of wave intensity `6W//m^2` strikes a small mirror of area `30cm^2`, held perpendicular to the approaching wave. The momentum transfered in `kgms^-1` by the wave to the mirror each second will be
A. `1.2xx10^(-10)`
B. `2.4xx10^-9`
C. `3.6xx10^-8`
D. `4.8xx10^-7`

Answer 1

Correct Answer - a
Momentum transferred in one second (i.e., force)
by em wave to the mirror is
`p=(2IA)/c=(2xx6xx(30xx10^-4))/(3xx10^8)`
`=1.2xx10^(-10) kgms^-1`