Light with an energy flux of `18 W cm^(-2)` falls on a non-reflecting surface at normal incidence. If the surface at normal incidence. If the surface has an area of `20 cm^(2)`, find the average force exerted on the surface during a span of 30 min.

Explanation

Total energy incident on the given surface in the given time interval is
`E=(18xx10^4 W//m^2)(20xx10^-4 m^2)(30xx60s)`
`= 6.48xx10^5 J`
There, the total momentum transferred to the given surface for complete absorption is
`Deltap=E/c =(6.48xx 10^5)/(3.0 xx 10 ^8)`
`= 2.16xx 10^-3 kg-m//s`
`:. F_(av )= (Deltap)/(Deltat)= (2.16xx10^-3)/(30xx60)`
`1.2xx 10^-6 N`.