CGPET 2015 Solved Paper

Fringe width in Young's double slit experiment is given by
β=

D

d

λ ...(i)
where, D = distance of the screen from the slits.
d = distance between S1 and S2
λ = wavelength of light.
when d is reduced
β′=

D

d′

λ ....(ii)
From Eqs. (i) and (ii), we get

β

β′

=

d′

d

<1[∵d′<d]
⇒β′>β
Thus, we can say that fringe width increases.