Physics - Wave Optics Question with Solution | TestHub

The fringe width in Young's double slit experiment is given by $\beta =\frac{\lambda D}{d}$

When the apparatus is immersed in water, the wavelength of light changes to ${\lambda }^{\prime }=\frac{\lambda }{\mu }$, where $\mu$ is the refractive index of water.

Since $\mu >1$, the new wavelength ${\lambda }^{\prime }$ is less than $\lambda$.

The new fringe width becomes ${\beta }^{\prime }=\frac{{\lambda }^{\prime }D}{d}=\frac{\lambda D}{\mu d}=\frac{\beta }{\mu }$

Since ${\beta }^{\prime }<\beta$, the fringe width will decrease.

Answer: the fringe width will decrease