Question

A central fringe of interference pattern produced by light of wavelength `6000 Å` is shifted to the position of 5th bright fringe by introducing thin film of `mu = 1.5`. Calculate thickness of the film.

Answer 1

Correct Answer - 6 micron
Here, `lambda = 6000Å = 6 xx 10^(-7) m`
`n = 5, mu = 1.5, t =?`
The basic relation used is that path difference introduced by film = Path diff. for the shift.
`(mu - 1) t = n lambda`
`t = (n lambda)/((mu - 1)) = 6 xx 10^(-6)m`
`= 6 micron`