Question

Which is the constructive interference formula for diffraction grating problems?

dsin =
dcos =
dcos = n
dsin = n

Answer 1

The formula for the brighter patches resulting from constructive interference and darker patches resulting from destructive interference in a diffraction grating is:

dsin(θ) = nλ

Here, d is the spacing between the grating, θ is the angle of light, n is the fringe order and λ is the wavelength. N has integer values only.

Destructive interference occurs between the fringes, so the formula for destructive interference becomes:

dsin(θ) = (n+1/2)λ, where n is again an integer.