Key Equations

Constructive interference	$\text{Δ}l=m\lambda ,$ for m = 0, ±1, ±2, ±3…
Destructive interference	$\text{Δ}l=(m+\frac{1}{2})\lambda ,$ for m = 0, ±1, ±2, ±3…
Path length difference for waves from two slits to a common point on a screen	$\text{Δ}l=d\text{sin}\theta$
Constructive interference	$d\text{sin}\theta =m\lambda ,\text{for}m=0,\text{±}1,\text{±}2,\text{±}3\text{,…}$
Destructive interference	$d\text{sin}\theta =(m+\frac{1}{2})\lambda ,\text{for}m=\mathrm{0,}\text{±}1\text{,}\text{±}2\text{,}\text{±}3\text{,}\dots$
Distance from central maximum to the mth bright fringe	$y_m=\frac{m\lambda D}{d}$
Displacement measured by a Michelson interferometer	$\text{Δ}d=m\frac{{\lambda }_0}{2}$