Question

For a sustained interference fringes in double slit experiment, the necessary condition/s is/are
A. The sources should be coherent
B. The intensities of both of the sources is to be equal
Which are the correct options in the above mentioned statements?
A. Both A, B
B. Only A
C. Only B
D. Neither A or B

Answer 1

Hint: The intensity of the light wave will be equivalent to the square of the amplitude of the light wave. Therefore as the amplitudes are the same, the intensity of the wave will also be the same. This is in the case of the light wave not in the case of the source. This will help you in answering this question.

Complete answer:
For a sustained interference fringes to be obtained, there are two major conditions to be mentioned. First of the two sources of the light wave which is being used for the interference process should be coherent in nature and they should be having the similar frequency. The second one is the requirement of the similarity of the amplitudes of the light waves used for the experiment. As we all know, the intensity of the light wave will be equivalent to the square of the amplitude of the light wave. Therefore as the amplitudes are the same, the intensity of the wave will also be the same. However the intensity of the wave is the same but the intensity of the source will not be the same. In short we can say that statement A given is correct.

Therefore the correct answer is option B.

Note:
The two wave sources which are considered to be perfectly coherent will be the waves with their frequency and waveform similar to each other. And their phase difference is also fixed. In short two waves can be said to be coherent when they are having a fixed relative phase.