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Q10.6  A beam of light consisting of two wavelengths, 650 nm and 520 nm, is used to obtain interference fringes in a Young’s double-slit experiment.

            (b) What is the least distance from the central maximum where the bright fringes due to both the wavelengths coincide?

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Let the nth bright fringe due to wavelength, \lambda_2 and (n − 1)thbright fringe due to wavelength\lambda_1 coincide on the screen. We can equate the conditions for bright fringes as:

n\lambda_2=(n-1)\lambda _1

520n=650n-650

650=130n

n=5

Hence, the least distance from the central maximum can be obtained by the relation:

X=n\frac{\lambda_2D}{d}=5*\frac{520*10^{-9}*D}{d}

Hence we can find out X if D and d are given.

Posted by

Pankaj Sanodiya

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