Radiation pressure: When an electromagnetic wave falls on a white, perfectly reflecting surface, it exerts a force F on that surface. If the surface is now painted a perfectly absorbing black, what will be the force that the same wave will exert on the surface?
A) 4F
B) 2F
C) F
D) F/2
E) F/4

Question

Quizplus · Accepted Answer

When an electromagnetic wave falls on a perfectly reflecting surface, the force it exerts is twice the radiation pressure (F = 2P/c, where P is the radiation pressure and c is the speed of light).

So, if the force exerted on a white, perfectly reflecting surface is F, the force exerted on a perfectly absorbing black surface will be half of F, or F/2.

Radiation Pressure: When an Electromagnetic Wave Falls on a White