In a YDSE with monochromatic light, fringes are obtained on a screen placed at some distance from the plane of slits. If the screen in moved by  5×10−2m  towards the slits, the change in fringe width is 3×10−5m . If the distance between the slits is  10−3m , then the wavelength of light used is

Distance between the slits d=10−3 m Screen distance  ΔD=5×10−2 m Change in fringe width Δβ=3×10−5 m Wavelength λ=? Fringe width β=Dλd                      Δβ=λd(ΔD)                   ⇒λ=d.ΔβΔD                            =(10−3)(3×10−5)5×10−2                              =6000×10−10m                       ∴ λ=6000 A0