A plane wave of wavelength 6250 A0  is incident normally on a slit of width 2×10−2 cm . The width of the principal maximum on a screen distant 50 cm will be

Wavelength  λ=6250 A0=6250×10−10 m   Slit width     a=2×10−2 cm=2×10−4 m   Distance of the screen  D=50 cm=0.5 m Width of central maximum=2λDa=2×6250×10−10×0.52×10−4                                              =312.5×10−3 cm.