Question

Which out of the following will not produce two coherent sources?
A. Lloyd’s mirror
B. Fresnel bi prism
C. Young’s double slit
D. prism

Answer 1

Lloyd's mirror is used to create two coherent sources out of phase with each other, which are from a single source and it gets reflected by a mirror.
Fresnel bi prism refracts the light from a single source in order to develop two in-phase virtual coherent sources. Young's double slit creates two coherent sources by the diffraction from the two slits. In this experiment, the phase is depending upon the position of the source with respect to the positions of the slits. These all may help you in answering this question.

Complete answer:
Lloyd’s Mirror is an optical instrument used to create two-source interference patterns. This is identical to the pattern created by laser light passing through two slits. A Fresnel Bi prism is a thin double prism which has been fixed base to base and has a very small refracting angle. This is identical to a single prism with one of its angles nearly $180{}^\circ$. The double-slit is also helpful in producing the two coherent sources. In this experiment, the phase is depending upon the position of the source with respect to the positions of the slits. A single prism cannot produce two coherent sources. Hence the answer from the option will be the single prism itself.

That is option D is the correct answer.

Note:
In Lloyd’s mirror, at a low angle, a diverging laser beam hits a front surface mirror. As a result, some of the beam reflects off the mirror to a screen, and some falls directly on the screen. This reflected beam becomes a virtual second source which will interfere with the direct beam. Making the separation between the laser and the mirror differed, the interference pattern on the screen will be changed.