In Young's double slit experiment with a monochromatic light of wavelength 2000 A0 , the fringe width is found to be0.6 mm . When the slits are now illuminated with a light of wavelength 3000 A0  the fringe width will be

Wavelength λ1=2000 A0 Wavelength λ2=3000 A0 Fringe width β1=0.6 mm Fringe width β2=? Fringe width β=λDd                      β1β2=λ1λ2                      β2=β1λ2λ1                          =0.6×30002000                ∴  β2= 0.9 mm