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The angular width of the central maximum in a single slit diffraction pattern is 60°. The width of the slit is 1 μm. The slit is illuminated by monochromatic plane waves. If another slit of same width is made near it. Young's fringes can be observed on a screen placed at a distance 50 cm from the slits. If the observed fringe width is 1 cm, what is slit separation distance ? (i.e. distance between the centres of each slit.)

1. 25 μm
2. 50 μm
3. 75 μm
4. 100 μm

Correct answer: 25 μm

Solution

The fringe width in Young's double-slit experiment is given by the formula β = (λ D)/(d), where β is the fringe width, λ is the wavelength, D is the distance to the screen, and d is the slit separation. Given the fringe width and the distance to the screen, the slit separation can be calculated, leading to the conclusion that the correct separation distance is 25 μm.

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