We know that the resultant intensity of the interference is I = 4a² cos² 8/2 From the above equation it is clear that the intensity at bright points is 4a² and at dark points it is zero. According to the law of conservation of energy, the energy cannot be destroyed. Here also the energy is not destroyed but only transferred from the points of minimum intensity to the points of maximum intensity.

Intensity varies from 0 to 4a², and the average is still 2a². It is equal to the uniform intensity 2a’ which will be present in the absence of the interference phenomenon due to the two waves. Therefore, the formation of interference fringes is in accordance with the law of conservation of energy.