Physics - Wave Optics Question with Solution | TestHub

The fringe width in Young's double slit experiment is given by $W=\frac{\lambda D}{d}$, where $\lambda$ is the wavelength, $D$ is the distance between the slits and the screen, and $d$ is the separation between the slits.

Given that the new distance between the slits and the screen is $D^{\prime }=2D$ and the new separation between the slits is $d^{\prime }=\frac{d}{2}$.

The new fringe width is $W^{\prime }=\frac{\lambda D^{\prime }}{d^{\prime }}=\frac{\lambda (2D)}{\frac{d}{2}}=4\frac{\lambda D}{d}=4W$.

Therefore, the fringe width increases four times.

Answer: increases four times.