Nodal lines are hyperbolas. Think about it, the definition of a hyperbola is the locus of all points whose distance to two fixed points have a constant difference. At distances much greater than the wavelength, the nodal lines appear as straight radial lines.
Path length difference
|nλ = ∆ℓ||(n + ½)λ = ∆ℓ|
|nλ = d sin θ||(n + ½)λ = d sin θ|
Small angle approximation
n = 0, 1, 2, 3, …
is the order
- Fringes are interference in space. (Beats are interference in time.)