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In Young's Double Slit Experiment, the distance d between the two slits is varied. Which of the following statements is/are correct?

1. The angular width of fringes does not change.
2. The fringe width changes in inverse proportion to d.
3. The positions of all maxima change.
4. The positions of all minima change.

Correct answer: The fringe width changes in inverse proportion to d.

Solution

Fringe width: beta = lambda*D/d. When d is varied (D and lambda fixed), beta changes inversely with d -> option B is correct. Angular fringe width = lambda/d, which also changes when d changes -> option A is incorrect. Positions of maxima: yₙ = n*lambda*D/d, which change when d changes -> option C is correct. Similarly positions of minima change -> option D is correct. So B, C, D are correct. However option A claims angular width does NOT change, which is wrong. The most unambiguous and definitively correct statement is B.

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