In Young's double slit experiment, the fringe width of the interference pattern produced on the screen is $2.4\,\mu$m. If the experiment is carried out in another medium having refractive index 1.2, the fringe width will be ______ $\mu$m.

JEE Main · 2026 · 05 Apr 2026 · Shift 1 · Wave Optics

In Young's double slit experiment, the fringe width of the interference pattern produced on the screen is

2.4 μ

m. If the experiment is carried out in another medium having refractive index 1.2, the fringe width will be ______

μ

(A)1.2
(B)2✓ Correct
(C)2.4
(D)2.88

Answer: (B)

Solution

Immersing the apparatus in a medium of refractive index

μ

shortens the wavelength to

λ / μ

, and since the fringe width

β = \frac{λ D}{d}

is proportional to the wavelength, it becomes

β^{'} = \frac{β}{μ}

. With

β = 2.4 μ m

and

μ = 1.2

β^{'} = \frac{2.4}{1.2} = 2 μ m

. The fringe width in the medium is

2 μ

JEE Main · 2026 · 05 Apr 2026 · Shift 1 · Single correct option

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