Key Equations

Constructive interference	$Δ l = m λ,$ for m = 0, ±1, ±2, ±3…
Destructive interference	$Δ l = (m + \frac{1}{2}) λ,$ for m = 0, ±1, ±2, ±3…
Path length difference for waves from two slits to a common point on a screen	$Δ l = d sin θ$
Constructive interference	$d sin θ = m λ, for m = 0, ± 1, ± 2, ± 3,…$
Destructive interference	$d sin θ = (m + \frac{1}{2}) λ, for m = 0, ± 1, ± 2, ± 3, \dots$
Distance from central maximum to the mth bright fringe	$y_{m} = \frac{m λ D}{d}$
Displacement measured by a Michelson interferometer	$Δ d = m \frac{λ_{0}}{2}$