5.5 Wave Behavior - Interference

We will consider the phenomenon of interference in one dimension only, though of course it is possible to extend the idea for more dimensions.

There are two basic rules for determining interference:

1. When two waves, moving in different direction, meet, their displacements at a given point in time, are added. However, whether this displacement is positive or negative must also be taken into account. The resulting displacement is that of the new wave.

2. After the interference has occurred, the original (in all aspects) waveforms continue moving in the same direction, unchanged.

Let us consider two special cases of interference, when both waves have the same amplitude, a. If the displacement of both waves is positive, for instance, the resulting wave when they meet will have a resulting amplitude of 2a.

When two waves meet to create a wave of larger amplitude, the condition is described as constructive interference

However, if the amplitudes (still a) are in opposite directions, they cancel out when the waves meet, to form a ‘wave’ of amplitude 0.

When two waves meet so that their combined amplitudes (in any direction) is less than either of their starting ones, the phenomenon is known as destructive interference. This of course happens with waves that are out of phase, or have amplitudes in opposite directions.