How does the fringe width in Young's double-slit experiment change when the distance of separation between the slits and screen is doubled?
Solution:
Fringe width, β = λD/d where all the symbols have their usual meanings. Now the distance between the slit and screen is doubled i.e D' = 2D ∴New fringe width β' = λ(2D)/d = 2β Thus fringe width gets also doubled.