In the Young's double slit experiment, the sources $\mathrm{S}_{1}$ and $\mathrm{S}_{2}$ are coherent, represented by $\mathrm{E}_{1}=\mathrm{E}_{0} \sin \omega \mathrm{t}$ and $\mathrm{E}_{2}=2 \mathrm{E}_{0} \sin \left(\omega \mathrm{t}+\frac{\pi}{3}\right)$ respectively. The slits are covered by
thin sheets of refractive index $\mu_{1}, \mu_{2}$ and thickness $\mathrm{t}_{1}$ and $\mathrm{t}_{2}$ respectively. The intensity of the source $S_{1}$ is $I_{0}$.
(i) Derive an expression for the intensity at the central point $\mathrm{O}$.
(ii) What is the condition for $\mathrm{O}$ to be the central bright fringe?