(3 waves) / ( 2seconds) =
(3/2) / (wave/second) = 1.5 per second = <em>1.5 Hz</em>.
<span>200 Hz is just another way of saying 200 vibrations/s .</span>
<span>In this case, the angle of incidence equals the angle of reflection at the point that the light ray strikes the surface. Light is also reflected when it is incident on a surface or interface between two different materials such as the surface between air and water, or glass and water.</span>