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In a Young's double slit experiment the fringe width is beta. If the slit separation is halved while the distance from the slits to the screen is doubled, the new fringe width becomes:

1. 0.25*beta
2. 2*beta
3. 4*beta
4. 8*beta

Correct answer: 4*beta

Solution

beta is proportional to D/d. With d -> d/2 and D -> 2D, beta scales by (2)*(2) = 4.

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