Question

If yellow light emitted by sodium lamp in Young's double slit experiment is replaced by monochromatic blue light of same intensity keeping other parameters constant the new fringe width will :

• A. Remain unchanged
• B. Increase
• C. Decrease
• D. Can't be predicted

Answer 1

The correct option is C Decrease

The fringe width in Young's double slit experiment is given by ,

$\beta =D\lambda /d$

where , $D=$ distance of screen from slits

$d=$ distance between slits

$\lambda =$ wavelength of the light used

It is clear from formula that ,

$\beta \propto \lambda$

Now , if blue light is used instead of yellow light , we know that

${\lambda }_Y>{\lambda }_B$

As the wavelength decreases due to blue light , therefore fringe width will decrease .