Q. 3. A plate of thickness t made of material of refractive index μ is placed in front of one of the slits in a double slit experiment. What should be the minimum thickness t which will make the intensity at the centre of the fringe pattern zero?

(a) λ( μ -1)/2

(b) λ( μ -1)

(c) λ/(2( μ -1))

(d) λ /( μ -1)

Ans: C

Sol: Path difference Δx = (2n−1)λ/2

(μ−1)t = (2n−1)λ/2

=> t = (2n−1)λ/(2(μ−1))

Put n=1 , t= λ/2(μ−1)