In a bi-prism experiment, the interference pattern is observed at the distance of 12 cm from the source and the wavelength of light is 500 nm. The distance between two virtual sources is 0.1 mm. Find the total number of fringes observed on the screen of length 30 cm.

Question

Question

Answer 1

CONCEPT:

Fresnel Bi-prism:

It is an optical device producing interference of light by joining two bases of thin prisms at a very small angle.
When a monochromatic light source is kept in front of bi-prism two coherent virtual sources are produced.
The Interference fringes are produced behind the bi-prism in a limited area and can see with the help of eyepiece.
Fringe width will be calculated with simple calculations.

F2 J.K 19.5.20 Pallavi D8

Width = (λ D)/d

Where,

λ = wavelength of source light,

D = distance between source and screen,

d = distance between two virtual coherent sources

Calculation:

Given, D = 12 cm = 12 × 10^-2 m, d = 0.1 mm = 1 × 10^-4 m, λ = 500 × 10^-9 m, Length of the screen = 30 cm = 300 mm

Width = (λ D)/d

\(width = \frac{{500 \times {{10}^{ - 9}} \times 12 \times {{10}^{ - 2}}}}{{1 \times {{10}^{ - 4}}}}\; = 6 \times {10^{ - 4}}m = 0.6\;mm\;\)

Each fringe width = 6 mm

Total number of fringes = Total fringe length/ each fringe width = 300 / 0.6 = 500 fringes.