<em><u>Interference of a wave</u></em> is the property a wave that occurs when two waves travelling in the same medium meet at a point or superpose at a point in the medium.
<em><u>Interference may be constructive or destructive. Constructive occurs when two identical waves travelling in the same medium in phase meet at a point.</u></em> The resulting wave has twice the amplitude of the individual waves.
<em><u>Destructive interference occurs when two waves travelling in the same medium meet and out of phase.</u></em> The resulting amplitude will be zero if the initial waves are identical, or the difference between the amplitude of the original waves if they are not identical.
Therefore; <em><u> If the two waves one with an amplitude 75 units and the other 74 units, are out of phase with each other, the resultant amplitude of the resulting wave will be 1 unit, the difference between the amplitude of the original waves.</u></em>
If the two waves have the SAME FREQUENCY and are exactly out of phase (180° apart), then the resultant wave will have the same frequency and an amplitude of 1 unit.
If the two waves do not have the SAME FREQUENCY, then their relative phase is meaningless.
