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Wave Optics — JEE physics STD 12 Science — Question

CBSE BoardEnglish MediumSTD 12 ScienceJEE physicsWave Optics1 Mark
MCQ
In Young's double slit experiment, if monochromatic light is replaced by white light
  • ✓
    (a) All bright fringes become white
  • B
    (b) All bright fringes have colours between violet and red
  • C
    (c) Only the central fringe is white, all other fringes are coloured
  • D
    (d) No fringes are observed
✓

Answer

Correct option: A.
(a) All bright fringes become white
(a) In conventional light source, light comes from a large number of independent atoms, each atom emitting light for about 10 . sec i.e. light emitted by an atom is essentially a pulse lasting for only 10 sec. Light coming out from two slits will have a fixed phase relationship only for $10 sec$. Hence any interference pattern formed on the screen would last only for $10 sec$, and then the pattern will change. The human eye can notice intensity changes which last at least for a tenth of a second and hence we will not be able to see any interference pattern. In stead due to rapid changes in the pattern, we will only observe a uniform intensity over the screen.

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