Is the answer to this angle of wedge question correct?

image of question: https://postimg.cc/8FCw5ZcM

using the diffraction grating formula dsinθ nlambda,

I put lambda = 650(10)^-9,
d = 1/(560x10^3),
n =1.5
and substituted these values to get 3.12x10^-5 degrees, which seems suspiciously small so im unsure

Reply 1

Joinedup

Original post by MonoAno555

But this is nothing to do with diffraction gratings.

What's happening is the light reflected from the top surface of the wedge is being interfered with by the light being reflected from the base of the wedge. Every place the thickness of the wedge results in a 2 way trip length for the light bouncing of the base of an integer number of wavelengths the result is constructive interference giving a maxima and every place where the thickness of the wedge results in a two way trip of an integer/2 number of wavelengths it gives destructive interference and a minima.
so the difference in thickness between a maxima and the nearest minima is λ/4, in the horizontal distance between 1 minima and the next the thickness has changed by λ/2

The next thing you need to worry about is the effect of refractive index on wavelength - when the wavelength of a light source is given it refers to the wavelength in a vacuum - light slows down (but does not change frequency) when it goes into a material with a refractive index >1 so the wavelength has to shorten.