Optics Problems - Numerical 19

19.

In Young's double slit experiment what is the intensity at a point on screen where the two waves arrive at a phase difference of (i) 60⁰ (ii) 90⁰ and (iii) 120⁰?

Suggested solution:

Let I₀ be the intensity of either of the interfering sources, the intensity I at a point P is  where d is the phase difference at p between the two disturbances.

(i) d = 60⁰ ; I = I_o cos² (30⁰)

(ii) d = 90⁰ ; I = 4I_o cos²(45⁰)

(iii) d = 120⁰; I = 4 I_o cos²(60⁰)