Question

If yellow light in the Young's double slit experiment is replaced with a red light, the fringe width will

• A. remains unaffected
• B. decreases
• C. increases
• D. first increases then decreases

Answer 1

The correct option is C increases

We know that
Fringe width, $\beta =\frac{D\lambda }{d}$
where $D$ is the distance between the screen and sources, $d$ is the distance between the slits and $\lambda$ is the wavelength
$\therefore \beta \propto \lambda \because {\lambda }_{red}>{\lambda }_{yellow}$
Therefore, fringe width will increases.