Why does a metal ball contacted with lamp black appear shining when dipped in water?
A metal ball contacted with lamp black appears shining when dipped in water. This is due to a phenomenon known as total internal reflection. When a beam of light passes from denser to rarer medium, and when the angle of incidence crosses a certain limit, entire light beam returns back, as if being reflected from the junction of the two mediums. The metal ball covered with lamp black has enough air pockets surrounding it. When light rays enter from the atmosphere into the water, refraction takes place. But when the beam of light passes from water into the air surrounding the ball, total internal reflection of the light beam take place. That is the reason; the ball appears shining when viewed from above.