# Can you solve this? It got me stumped!?

One of the strange results of quantum physics research is that light consists of innumerable particles called photons. Photons effectively have weight and hence possess momentum. When they strike a surface they transfer momentum to the surface, thus exerting a force on it. Suppose that each of two identical photons (same effective mass) strikes a surface. The surfaces are identical except one is black and absorbs the photon, while the other is white and reflects the photon back in the direction from which it came. (All photons have the same speed). In comparing the momentum transferred to the surfaces, you can say....

a) p(white) > p(black)

b) p(white) = p(black)

c) p(white) < p(black)

d) Need to know the effective mass.

### 1 Answer

- jeffdanielkLv 42 months ago
The momentum given to the white surface is twice the momentum given to the black surface. When a photon, or anything else, bounces off a surface, it delivers more momentum than if it stuck to the surface. This is true even for a rubber ball and a clay ball hitting a surface. If they have the same mass and velocity, the rubber ball transfers twice as much momentum to the surface as the clay ball that sticks.