# Interference from Thin Films

1. Sep 11, 2015

### Jimbob999

1. The problem statement, all variables and given/known data
A thin film with an index of refraction of 1.60 is placed in one of the beams of a Michelson interferometer. If this causes a shift of 8 bright fringes in the pattern produced by light of wavelength 580 nm, what is the thickness of the film?

1.5 µm

2.9 µm

3.9 µm

7.7 µm

16 µm

2. Relevant equations

2L = (m + 1/2) lambda/n2 (maxima - bright film in air)

3. The attempt at a solution

2L = 8.5 (5.7x10^-7 / 1.6)

L = 1.5µm

I am just trying to find out whether I used the right formula here, as it states in the question 'bright fringes', so I am assuming that bright film in air formula applies.
Also how would I know to use the other formula for minima?

Thanks.

2. Sep 11, 2015

### andrevdh

What physics process is at work in this problem?
How do bright fringes come about?

Last edited: Sep 11, 2015
3. Sep 11, 2015

### Jimbob999

Intereference, Interference?

But that doesn't really get me anywhere...

4. Sep 12, 2015

### Jimbob999

Anyone can help?