- Mathematically interference phenomenon can takes place between two waves of same frequency and different amplitudes. But for observable interference, the amplitudes of the waves should be equal. In this case,
From equation (11), the maximum intensity is 4A2 and minimum intensity is zero. In the phenomenon of interference the energy is not destroyed but is only redistributed from the positions of minimum intensity to those of maximum intensity. At the maximum intensity positions the intensity due to the two waves should be 2A2 but it actually 4A2. As shown in figure, the intensity varies from 0 to 4A2 and the average is still 2A2. It is equal to a uniform intensity of 2A2 which will be present in the absence of interference phenomenon between two waves. Hence the formation of maxima and minima is due to interference of waves is in accordance with the law of conservation of energy.
The phase difference between the two waves must remain constant, it will not change with time. If the phase difference between the waves continuously changes,then the positions of the maximum and minimum intensities do not remain fix.
The waves must travel in the same direction because with increase in obliquity between the waves, the resultant intensity decreases.
