If the distance between the double slit and the screen is doubled and width of the double slit is halved then what will be the new fringe width.

Explanation

`beta'=(lambda D')/(d')`
i.e., `beta'=lambda(2D)/(d/2)`
or `beta'=4((lambdaD)/(d))`
i.e., `beta=4beta.`
Hence New fringe width will be four times the old fringe width.
Percentage increases in the fringe width `=(beta'-beta)/(beta)xx100=300%`