In Young's double-slit experiment, light of wavelength $600$ nm falls on two slits $0.5$ mm apart and the fringes are viewed on a screen $2$ m away. Find the fringe separation.

Fringe separation $y = \dfrac{\lambda D}{d} = \dfrac{600 \times 10^{-9} \times 2}{0.5 \times 10^{-3}} = 2.4 \times 10^{-3}$ m $= 2.4$ mm. Using $D = 1$ m or $d = 1$ mm halves the result.