Question

Interference fringes were produced in Young’s double slit experiment using light of wavelength 5000 Å. When a film of material 2.5 × 10^–3 cm thick was placed over one of the slits, the fringe pattern shifted by a distance equal to 20 fringe widths. The refractive index of the material of the film is 

(a) 1.25 

(b) 1.33 

(c) 1.4 

(d) 1.5

Answer 1

Correct option (c)

Explanation:

Fringe width β = λD/d .....(i)

where D is the distance between the screen and slit and d is the distance between two slits. 

When a film of thickness t and refractive index μ is placed over one of the slit, the fringe pattern is shifted by distance S and is given by