Reflection & Refraction
When waves strike a material boundary i.e. go from one medium to another the following may happen:
This occurs when a wave travelling in one medium strikes the surface of a different medium and changes direction so that it returns back into the medium in which it was originally travelling in. Simply put the waves bounce back. Examples of reflection are light waves striking a mirror or echoes in which sound waves are reflected of a solid surface.
When waves undergo reflection the angle the incoming waves make with the surface is equal to the angle of the reflected waves. This is the Law of Reflection and can be written as;
The angle of incidence = the angle of reflection
Reflection in use – The Periscope
A periscope is an optical instrument used predominantly in submarines so that the submarine crew can see what is happening above the surface of water without having to surface. The animation below describes how a periscope works.
The speed at which a wave travels is dependant upon the medium in which it travels along or through. The speed of a wave changes when a wave moves from one medium to another. This change in wave speed is accompanied by a change in wavelength and change in direction. It is this change of direction or bending of the wave as it passes from one medium to another that is called refraction.
Effects of Refraction
Refraction is why water appears shallower than it really is. In the diagram below the rays of light from the fish are refracted away from the normal as the leave the water. This bending of the light is not registered by the eye rather it seems as if the rays come from an imaginary fish higher in the fish bowl. Therefore the apparent position of the fish is higher than the real position.