Light in certain cases may be considered as a stream of paerticles called photons. Each photon has a linear momentum `h/lamda` where h is the Planck's constant and `lamda` is the wavelength `lamda` is incident on a plane mirror at an angle of incidene `theta`. Calculate the change in the linear momentum of a photon as the beam is reflected by the mirror.

Explanation

`P_((ncidence)(h/lamda)costhetaveci-(h/lamda0sintheta vecj`
`P_(Reflected)=-(h/lamda)costheta veci-(h/lamda)sintheta vecj`
The change in momentum will be only in the x-axis direction i.e.
`|/_\P|=(h/lamda_costheta-(h/lamdacostheta)
`=((2h)/lamda) costheta`