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˚? 

Answer 1

For 1^st minimum, sinθ₁ = `λ/"a"`. For θ₁= 45°, `λ/"a"` = sin 45° = `1/sqrt2` 

∴ Ratio of slit width to wavelength, a : λ = `sqrt2` :1