A narrow slit of width 1 mm illuminated by monochromatic light of wavelength 600 nm. The distance between the first minima on either side of a screen at a distance of 2 m is 

For first dark fringe on either side, d $\sin \theta =\lambda$ Or $\frac{dy}{D}=\lambda$, $\therefore y=\frac{\lambda D}{d}$

Therefore, distance between two dark fringes on either side $=2y=\frac{2\lambda D}{d}$

Substituting the values, we have Distance $=\frac{2\left(600\times {10}^{-6}mm\right)\left(2\times {10}^{3}mm\right)}{\left(1.0mm\right)}=2.4mm$