Read the information given below to answer

In Young’s double slit experiment as shown in figure, interference of light waves were observed on the screen. Thomas Young made two pinholes S₁ and S₂ (very close to each other) on an opaque screen in front of parent source S

S₁ and S₂ behaved as coherent sources, and produced interference patten on the screen which has alternate bright fringe and dark fringes. This experiment proved Huygen’s wave theory of Light.

In YDSE the distance between two consecutive bright fringes is given by 3 mm. What would be the fringe width if YDSE is performed in a medium of refractive index 1.2?

2.5 mm

We know,

Distance between two consecutive bright fringes is equal to fringe width.

∴ Fringe width β = 3 mm = $\frac{\lambda D}{d}$

If system is immersed in a medium , wavelength will reduce by a factor of $\mu$

then \(β_{new} = \frac{β}{µ} = \frac{3}{1.22}\) = 2.5mm