Key idea Angular position of n th minima in single slit diffraction by a monochromatic source is given by α‌sin‌θn=nλ (n=1,2,3...) Where, λ= wavelength and α= slit width As we know, ‌‌sin‌θn=‌
nλ
α
So, for first minima i.e., n=1 So, for first minima i.e., n=1 ⇒sin‌θ=‌