Physics · Interference: Young's double-slit experiment and expression for fringe width, coherent sources and sustained interference of light

In Young's experiment with white light, the central fringe is white. If now a tr

In Young's experiment with white light, the central fringe is white. If now a transparent film is introduced in the upper beam coming from the top slit, then the white fringe:

  • A. moves downward
  • B. moves upward
  • C. remains at the same place
  • D. totally disappears

Step-by-step solution

Introducing a transparent film in the upper beam increases its optical path length. To maintain zero path difference at the central bright fringe, the fringe shifts downward where the upper beam's geometrical path is shorter, thereby compensating for the added optical path.
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