JEE Main 2026 — Apr 4, Shift 2 — Physics solution

JEE Main2026Apr 4, Shift 2Physics

In a double slit experiment, when one of the slits is covered by a transparent mica sheet of refractive index 1.56, the central fringe shifts to the position of 7 $^{t h}$ bright fringe, obtained with both slits uncovered. If the light source wavelength is 450 nm, the thickness of mica sheet is $α \times 1 0^{- 9} m$ . The value of $α$ is _______.

Your answer

Solution

Fringe shift on inserting a sheet: $Δ y = (μ - 1) t \frac{D}{d}$ . Equating to the position of the 7 $^{t h}$ bright fringe ( $7 λ D / d$ ):

$(μ - 1) t \frac{D}{d} = 7 \frac{λ D}{d} \Rightarrow (μ - 1) t = 7 λ$ .

$(1.56 - 1) t = 7 \times 450 nm \Rightarrow 0.56 t = 3150 nm$ .

$t = \frac{3150}{0.56} = 5625 nm = 5625 \times 1 0^{- 9} m$ .

$∴ α = 5625$ .

← Back to full paper

Practice more Physics

Concept-wise practice with instant solutions on Fundamenthol.

Start practicing →