Question

In Fresnel’s biprism experiment, coherent sources are obtained from an incoherent source using division of
(A) Amplitude
(B) Wavefront
(C) Phase
(D) None

Answer 1

Hint: You need to apply the basics of the Fresnel biprism in order to solve this question. So you should firstly know about Fresnel biprism and its applications. You should also know about the coherent and incoherent sources, which will help you to answer this question.

Complete step by step answer:
A Fresnel biprism is a type of prism having a double thin prism that is placed over each other having a very low refracting angle. In the experiment, a light generated from a single source is made to pass through two virtual sources. It is due to the refraction in a prism, and thus the two sources act as coherent sources.

As we see the figure, it can be seen that the light falls on the prism, emerging from the slit when the light rays fall on the prism and get divided into two. One goes to the lower half of the prism, which appears to originate from the virtual source $S_1$ . On the other hand, the second goes to the upper half, which appears to come from the virtual source $S_2$ . The interference fringes can be observed in the region XY, which will be visible from the eyes. Interference will only take place when the source is coherent in nature. The incoherent source can be converted into a coherent source only by the division of the wavefront.

Thus, the interference in this prism is obtained by the division of the wavefront.

Note:
You can be confused between the amplitude and wavefront, but the answer cannot be amplitude. It is so because the wavefront of the incident wave is divided to get two virtual sources.