# PGRE | Michelson Interferometer Equation

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1. Feb 27, 2012

### CanIExplore

1. The problem statement, all variables and given/known data
I am having trouble understanding how I would apply the Michelson Interferometer equation to a problem on the PGRE. Here is a link to a diagram displaying the interferometer as well as the equation which is very similar to the way the topic is shown in my REA pgre book.

http://hyperphysics.phy-astr.gsu.edu/hbase/phyopt/michel.html
2. Relevant equations
2d=mλ

3. The attempt at a solution
I just don't understand what the variable d is referring to. In the REA book, it says that if the fixed mirror on the right is moved through some distance d, then the number of circular fringes m moves in. And using the aforementioned equation, you can solve for the wavelength of the light. Can anyone explain how this works?

2. Feb 27, 2012

### Delphi51

d is the change in the distance L; it is how far the movable mirror moves.
2d is the change in the path the light takes going to the movable mirror and back.