Calculating Thin Film Thickness Using Interference Patterns

[Jimbob999]

Homework Statement

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

Homework Equations

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

The Attempt at a Solution

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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.

 

[andrevdh]

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

 

[Jimbob999]

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

Intereference, Interference?

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

 

[Jimbob999]

Anyone can help?