Question

What happens if the monochromatic light used in Young’s double slit experiment is replaced by white light?

• A. No fringes are observed.
• B. All bright fringes become while.
• C. All bright fringes have colour between violet and red.
• D. Only the central fringe is white and all other fringes are coloured.

Answer 1

The correct option is D

Only the central fringe is white and all other fringes are coloured.

1. White light consists of waves of innumerable wavelengths ranging from violet to red color.
2. So if monochromatic light in Young’s double-slit experiment is replaced by white light, then the waves of every wavelength form their separate interference patterns.
   
3. The resultant impact of these patterns is obtained on the screen. The path distinction between waves ranging from S1and S2 at the location R of the central fringe is zero that is for the point R of the screen so the path difference will be zero.
   Hence the waves of all colors reach a middle point R in the same phase.
4. So the central fringe is white.
5. As the fringe dimension that is the wavelength will increase so as colors denoted by VIBGYOR so on either aspect of it some colored fringes are obtained in the order of color VIBGYOR.
6. That's the violet fringe seems first and therefore, the red in the last.
7. When this the fringes of many colors overlap at every purpose of the screen then the screen seems uniformly illuminated.
8. Thus, if we tend to use white light in place of monochromatic light the central fringe is white, containing on either aspect several colored fringes in order VIBGYOR and therefore, the remaining screen seems uniformly illuminated.