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At two points P and Q on screen in Young's double slit experiment, waves from slits S1 and S2 have a path difference of 0 and λ/4, respectively. The ratio of intensities at P and Q will be:

1. 2: 1
2. √2: 1
3. 4: 1
4. 3: 2

Correct answer: 2: 1

Solution

At P path difference 0 so I_P = Imax. At Q path difference lambda/4 gives phase pi/2, so I_Q = Imax cos^2(pi/4) = Imax/2. Ratio I_P:I_Q = 2:1.

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