Derive formula for force on a plate of mass m if a light of intensity I is illuminated on it within area A, wavelength is lamda . derive formula of force for 4 following cases

1.when the light is absorbed totally,the momentum of light is totally transfered in elestic collision.

initial momentum associated with light=p=U/c

So change in momentum/time hence force=-U/c

2) When the light is reflected totally,

change in momentum/time=-p-p=-2p=-2U/c, hence force.