Question

Young’s double slit experiment is performed with 589 nm light and a distance of 2 m between the slits and the screen. The tenth interference minimum is observed 7.26 mm from the central maximum. The spacing of the slits is __________ mm . 

Answer 1

The condition far interference minimum is

The first minimum is described by m = 0 and the tenth by m = 9

Now far 10th minimum sin θ =  λ/d (9 + 1/2) ⇒ sin θ = 9.5 λ/d also tan θ  = y/D

but far small angle sinθ ≅ tan θ