Physics - Wave Optics Question with Solution | TestHub

Intensity of dark and bright fringes is given by
$I_{Dark}={\left(\sqrt{I_1}-\sqrt{I_2}\right)}^2$
$I_{Bright}={\left(\sqrt{I_1}+\sqrt{I_2}\right)}^2$

When there is no glass plate
$I_1=I_2=I_0$
$\therefore I_{\mathrm{D}\mathrm{a}\mathrm{r}\mathrm{k}}=0$ and $I_{\mathrm{B}\mathrm{r}\mathrm{i}\mathrm{g}\mathrm{h}\mathrm{t}}=4I_0$

But when glass plate is introduced in the path of one of the slits,
$I_2=\frac{I_0}{2}$
$\therefore$ $I_{\mathrm{D}\mathrm{a}\mathrm{r}\mathrm{k}}\ne 0$ increases and $I_{\mathrm{B}\mathrm{r}\mathrm{i}\mathrm{g}\mathrm{h}\mathrm{t}}$ decreases.

Fringe width remains same.