JEE Main · 2022 · 29 Jul 2022 · Shift 1 · Wave Optics

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Two light beams of intensities 4I and 9I interfere on a screen. The phase difference between these beams on the screen at point A is zero and at point B is

π

. The difference of resultant intensities, at the point A and B, will be ______ I.

Answer: 24

Solution

For interference, the resultant intensity is

I_{net} = I_{1} + I_{2} + 2 I_{1} I_{2} cos ϕ

. At point A (

ϕ = 0

I_{max} = (I_{1} + I_{2})^{2} = (9 I + 4 I)^{2} = (3 I + 2 I)^{2} = 25 I

. At point B (

ϕ = π

I_{min} = (I_{1} - I_{2})^{2} = (9 I - 4 I)^{2} = (3 I - 2 I)^{2} = I

. The difference is

I_{max} - I_{min} = 25 I - I = 24 I

JEE Main · 2022 · 29 Jul 2022 · Shift 1 · Integer answer

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