JEE Main 2026 Apr 6 Shift 1, Physics Q11: Young’s Double Slit Experiment

JEE Main2026Apr 6, Shift 1Physics

In interference experiment the path difference between two interfering waves at a point A on the screen is $λ /3$ , where $λ$ is the wavelength of these waves, and at another point B the path difference is $λ /6$ . The ratio of intensities at points A and B is _____.

A
$3$
B
$4$
C
$\frac{1}{3}$
D
$\frac{1}{4}$

Solution

For two equal-intensity sources, $I = 4 I_{0} cos^{2} (Δ ϕ /2)$ , where $Δ ϕ = \frac{2 π}{λ} \cdot Δ x$ .

At A: $Δ ϕ_{A} = \frac{2 π}{3}$ , so $I_{A} = 4 I_{0} cos^{2} (π /3) = 4 I_{0} (1/2)^{2} = I_{0}$ .

At B: $Δ ϕ_{B} = \frac{π}{3}$ , so $I_{B} = 4 I_{0} cos^{2} (π /6) = 4 I_{0} (3 /2)^{2} = 3 I_{0}$ .

$\frac{I _{A}}{I _{B}} = \frac{1}{3}$ .

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JEE Main 2026 Apr 6 Shift 1, Physics Q11: Young’s Double Slit Experiment

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