If the monochromatic source in Young's double slit experiment is replaced by white light, then
- Interference pattern will disappear
- There will be a central dark fringe surrounded by a few coloured fringes
- There will be a central bright white fringe surrounded by a few coloured fringes
- All bright fringes will be of equal width
Answer
(3) There will be a central bright white fringe surrounded by a few coloured fringes
Solution
At the centre the path difference is zero for every wavelength, so all colours interfere constructively there: the central fringe is bright and white.
Away from the centre the fringe width = Dd is different for different colours, so the next few fringes are coloured (blue nearest, red farthest) and the pattern soon fades out.
Answer: (3)