Question

If the monochromatic source in Young's double slit experiment is white light, then ____________.

Options

• fringe pattern in not observed

• central fringe is white and the fringe closest on either side of the central white fringe is red

• central fringe is white and the fringe closest on either side of the white fringe is blue

• central fringe is white and the fringe closest on either side of the white fringe is dark

Answer 1

If the monochromatic source in Young's double slit experiment is white light, then central fringe is white and the fringe closest on either side of the central white fringe is red.

Explanation:

The interference patterns due to different component colours of white light overlap. The central bright fringes for different colours are at the same position. Hence, the central fringe is white.

For a point P for which `S_2P - S_1P = lambda_b/2 where lambda_b (= 4000 Å)` represents wavelength of blue light, the blue component will be absent and the fringe will appear red in colour.

Slightly farther away where `S_2Q - S_1Q = lambda_b = (lambda_r)/ 2` where

`lambda_r (= 8000  Å)`is the wavelength for the red colour, the fringe will be predominantly blue. Thus, the fringe closest on either side of the central white fringe is red and the farthest will appear blue.