JEE Advanced 2024 — Paper 2 — Question 40

In a Young's double slit experiment, each of the two slits A and B, as shown in the figure, are oscillating about their fixed center and with a mean separation of 0.8 mm . The distance between the slits at time $t$ is given by $\mathrm{d}=(0.8+0.04 \sin \omega \mathrm{t}) \mathrm{mm}$, where $\omega=0.08 \mathrm{rads}^{-1}$. The distance of the screen from the slits is 1 m and the wavelength of the light used to illuminate the slits is $6000 AA$. The interference pattern on the screen changes with time,while the central bright fringe (zeroth fringe) remains fixed at point O

The $8^{\text {th }}$ bright fringe above the point O oscillates with time between two extreme positions. The separation between these two extreme positions, in micrometer ( $\mu \mathrm{m}$ ), is