A beam of white light is incident normally on a plane surface absorbing 70% of the light and reflecting the rest. If the incident beam carries 10 W of power, find the force exerted by it on the surface.
If the surface is fully reflecting surface, then force exerted will be
As 30% is reflecting surface then 3 W of power is used in force exerted by the reflecting surface.
Hence force by reflecting part is 
.
If the is fully absorbing then force exerted is
=
As 70% is absorbing surface then 7 W of power is used in force exerted by the absorbing surface.
Hence force by absorbing part is 
=
.
Hence total force is F=
=2
F=
F =
1