IGNOU BPHCT 137 2026 - Obtain the expression for shift in fringes when a thin transparent she

Question

Obtain the expression for shift in fringes when a thin transparent sheet is introduced in the path of one of the waves in a double slit interference experiment.

19 Jan 2026

Answer :

Word Count : 520

In a double slit interference experiment, when a thin transparent sheet is introduced in the path of one of the waves, the optical path difference between the two waves changes. This change leads to a shift in the interference fringes observed on the screen. Consider the basic setup of the double slit experiment where two coherent light waves originate from two slits separated by a distance ( d ) and interfere on a screen placed at a distance ( D ) from the slits. The fringe width (distance between two consecutive bright or dark fringes) is given by [ \beta = \frac{\lambda D}{d} ] where (\lambda) is the wavelength of the light used. Initially, the two waves travel equal distances, and the interference pattern forms

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