Question

In Michelson interferometer sharp circular fringes are observed. A very thin plate with optical thickness equal to twenty wavelengths of the light being used in inserted into one of the interferometer arms. What is the number of bright fringes that cross the field of view?

• A. 10
• B. 20
• C. 30
• D. 35

Answer 1

Optical thickness of plate $=(\mu -1)t=20\lambda$ We know that number of fringes crossing the field of view are given by $n=\frac{2(\mu -1)t}{\lambda }$ $=\frac{2\times 20\lambda }{\lambda }=40$