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In Young's experiment the distance between the two slits is halved and the distance between the screen and the slits is made three times. The width of the fringe then ________.

Asked in GUJCET 2008 · Fringe width and fringe position

• (1) becomes 6 times
• (2) becomes 4 times
• (3) becomes half
• (4) remains the same

Step-by-step solution

Why the other options are wrong

• (2) 4 times is the answer to the version of this question in which the screen distance is only doubled: 2 × 2 = 4. Here it is tripled, so the factor is 3 × 2 = 6.
• (3) This treats the fringe width as proportional to d, so that halving d halves the width. In β = (λ D)/d the slit separation sits in the denominator.
• (4) The two changes do not cancel; both of them widen the fringes. They would cancel only if d were made three times larger along with D.

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