Physics - Wave Optics Question with Solution | TestHub

The fringe width in an interference pattern is given by $W=\frac{\lambda D}{d}$, where $\lambda$ is the wavelength of the light used.

Sodium light is predominantly yellow, while violet light has a shorter wavelength. Thus, ${\lambda }_{violet}<{\lambda }_{sodium}$.

Since the fringe width is directly proportional to the wavelength ($W\propto \lambda$), a decrease in wavelength results in a decrease in the fringe width.

Therefore, when violet light replaces sodium light, the fringe width decreases.

Answer: Fringewidth decreases.