question_answer

What will be the effect on the interference fringes in Young's double slit experiment when, (i) the monochromatic source is replaced by another monochromatic source of shorter wavelength? (ii) monochromatic source is replaced by a source of white light. Justify your answer in each case?                               

Answer:

                 (i) Fringe width, \[\beta =\frac{D\lambda }{d}.\] With monochromatic source of shorter wavelength \[\lambda ,\]fringe width \[\beta \]decreases.  (ii) At the centre of the screen, the path difference is zero for all the wavelengths. So the central fringe is white. As the violet colour has lowest \[\lambda \] the closest fringe or either side of central white fringe is violet, while the farthest fringe is red. After a few fringes, the fringe pattern becomes indistinct due to large overlapping.