A double slit experiment is performed with light of wavelength 500nm. A thin film of thickness 2μm and refractive index 1.5 is introduced in the path of the upper beam. The location of the central maximum will:
A
remain unshifted
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B
shift downward by nearly two fringes
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C
shift upward by nearly two fringes
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D
shift downward by ten fringes
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Solution
The correct option is C shift upward by nearly two fringes When we introduce a thin film of some thickness in the path of the upper beam, actually we are increasing the optical path of the upper beam.
Now, for the same path difference, the lower beam will shift upwards so that it is elongated such that the path difference remains unchanged.