Question

3.c Compare and contrast the interference fringe patterns of a Fabry-Perot interferometer and aMichelson interferometer, with each interferometer illuminated in the same way by a divergent laser light beam and with equal path differences contributing to the interference. Be sure to note both how the patterns are similar and why the patterns are different.

Answer 1

First let's look at there construction:

both interferometer gives circular fringes at the screen.

Michelson Interferometer:

Fabry-perot interferometer

As both interfermoeter produce circular interference but the difference is in construction:

Michelson one has Beam splitter, whic splits incident beam into two perpendicular directions toward M1 and M2 mirrors, by reflection 180 degrees phase change would occur at mirrors and when they come back after reflection the beam splitter reflect it to the screen. Therefore due to phase difference between the rays of M1 and M2 a circular interference is produced.

While in Fabry-perot interferometer, two partially reflection mirrors are used, those mirror are designed to pass the light ray from side and reflect from other such that between two mirrors light will trap and several reflection occurs and due to reflection phase difference pops in incidents rays which then reaches screen and produce circular interference.
So, patterns are similar but difference is in the interference of incident waves.