Given, λ=6500Å=6500×10−10m,θ=30° According to the diffraction pattern of single slit, a‌sin‌θ=nλ where, n= order of secondary minima =1 ⇒ a‌sin‌30°=1×(6500×10−10) ⇒
a
2
=6500×10−10 or a=13000×10−10 =1.3×10−6m=1.3‌micron