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What is the effect on the interference fringes in a Young's double-slit experiment due to each of the following operations : the monochromatic source is replaced by a source of white light ? (In each operation, take all parameters, other than the one specified, to remain unchanged.) |
| Answer» SOLUTION :The interference patterns due to different COMPONENT colours of white LIGHT overlap (INCOHERENTLY). The central bright fringes for different colours are at the same position. Therefore, the central fringe is white. For a POINT P for which `S_2P-S_1P =lambda_(b)//2`, where `lambda_(b) (approx 4000 Å)` represents the wavelength for the blue colour, the blue component will be absent and the fringe will appear red in colour. Slightly farther vay where `S_2Q- S_1Q = lambda_b= lambda_2//2` where `lambda_r (approx 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. After a few fringes, no clear fringe pattern is seen. | |