A plate is kept in front of a beam of photons. The plate reflects 40% of the incident photons and absorbs the remainder. If the plate absorbs energy at a rate `1200J^(-1)s`, find the net force acting on it.

Explanation

Energy incident on the plate `=(1200xx100)/(60)=2000Js^-1`
`nhc=2000` …(i)
Initial momentum of photons `=(nhv)/c`
Final momentum of photons
`=(40)/(100)xx(nhv)/(c)=(0.4njv)/(c)`
Force acting on the plate
=Rate of change of momentum
`=(0.4nhv)/(c)-(-(nhv)/(c))=(1.4nhv)/(3xx10^8)` ... (ii)
Substituting the value of nhv from Eq. (i) in Eq. (ii), we get the force acting on the plate.