Wave Behavior

Wave Behavior When waves encounter new mediums, barriers, or other waves they can behave in different ways. In physics these behaviors are described using some of the following terms.

Reflection  The word "reflection" is used in everyday life to describe what we see in a mirror or on the surface of the water. In physics, a reflection is when a wave encounters a new medium that acts as a barrier, causing the wave to return to the original medium. The wave "reflects" off the barrier at an angle that is incident to the angle of the wave hitting the barrier.

Refraction Refraction of a wave occurs when a wave changes direction upon moving from one medium to another. Along with the change of direction, refraction also causes a change in the wavelength and the speed of the wave. The amount of change in the wave due to refraction is dependent on the refractive index of the mediums.

Diffraction  Diffraction occurs when a wave stays in the same medium, but bends around an obstacle. This can occur when the wave encounters a small object in its path or when the wave is forced through a small opening. An example of diffraction is when a water wave hits a boat and bends around the boat. The waves after the boat are changed or diffracted.

An example of a diffracted wave passing through a small opening.

Interference  When one wave comes into contact with another wave this is called interference. When the waves meet the resulting wave will have the amplitude of the sum of the two interfering waves. 

Constructive Interference When crests overlap with crests and troughs overlap with troughs. Destructive Interference When crests overlap with troughs and troughs overlap with crests.

Depending on the phase of the waves the interference can be constructive or destructive. If the resulting wave has a higher amplitude than the interfering waves, this is constructive interference. If it has a lower amplitude, this is called destructive interference.

Constructive Interference We say these waves are “in phase” meaning that the crests line up (or are “in phase”) with the crests and the troughs line up with the troughs.

The result of constructive interference is a bigger wave, a louder sound, (greater amplitude) etc.

Destructive Interference We say these waves are “out of phase” because they are 180 degrees off from eachother. In other words, crests line up with troughs and vice versa.

The result of destructive interference is a flat line or no wave, sound, etc.