Question

PHYSICS - GEOMETRIC PHYSICS - MICHELSON INTERFEROMETER

From a textbook chapter entitled: "Interference"

QUESTION: If one arm of a Michelson interferometer contains a tube 2.5 cm long that is first evacuated and then slowly filled with air (n=1.0003), how many fringes will cross the center? Assume light of 600 nm wavelength.

Please highlight any relevant equations, and show a step-by-step worked out solution.

Thanks

Answer 1

In the experiment, the mirror is moved through a known distance d and the number N of fringes appearing or disappearing at the centre is counted.

For one fringe to appear or disappear, the mirror must be moved through a distance of λ/2

d = N ( λ / 2 )

Rearrange for N

N =  2 d / λ

Substitute given values

N = 2 ( 0.025 m ) / 600 x 10^-9

= 83333 fringes