Q.

In Young’s double slit experiment, if the separation between coherent sources is halved and the distance of the screen from the coherent sources is doubled, then the fringe width becomes                [2020]

1 double  
2 half  
3 four times  
4 one-fourth  

Ans.

(3)

Fringe width, β=Dλd

d becomes half d'=d2

D doubles, soD'=2D

New fringe width, β'=2Dλ(d2)=4β