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In Young's double slit experiment the distance between the two slits is equal to the wavelength of the light used. The maximum number of bright fringes that can be obtained on the screen is ________.

Asked in GUJCET 2017 · Fringe width and fringe position

Answer: (2) 3

Step-by-step solution

Given: d = λ in a two-slit experiment.

Idea: a bright fringe needs d sin θ = nλ, and sin θ can only lie between -1 and +1, which caps the order.

With d = λ the condition becomes sin θ = n, so the only allowed orders are n = -1, 0, +1.

That is the central maximum together with one first-order maximum on each side, those two lying at θ = 90°, along the plane of the slits.

The maximum number of bright fringes is 3.

Why the other options are wrong

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