Question

What must be the ratio of the slit width to the wavelength for a single slit to have the first diffraction minimum at 45.0°?

Answer 1

Data : θ = 45°, m = 1 

a sin θ = mλ for (m = 1, 2, 3… minima) 

Here, m = 1 (First minimum)

∴ a sin 45° = (1) λ

This is the required ratio.