Question

In figure young’s double slit experiment Q is the position of the first bright fringes on the right side of O, p is the 11th fringe on the other side as measured from Q If λ = 6000 Å then S₁B will be ___________ m.

(A) 6.6 × 10^–6

(B) 3.3 × 10^–6

(C) 6 × 10^–6

(D) 6 × 10⁺⁶

Answer 1

The correct option is  (C) 6 × 10^–6.

Explanation:

Q → position of 1st bright fringe 

P → position of 11st bright fringe 

Measured from Q. Hence P is the position of 10th bright fringe from the central bright fringe. 

∴ n = 10

Path different at point P is = S₁P – S₂P and path difference = nλ = 10 × 6000 × 10^–10 m = 6 × 10^–6 m

Path difference = S₁P – S₂P ≈ S₁B (looking at diagram)

∴ S₁B = 6 × 10^–6m.