Q: Two slits are made one millimetre apart and the screen is placed one meter away. What should the width of each slit be to obtain 10 maxima of the double slit pattern within the central maximum of the single slit pattern.

Sol: $\large 10 \frac{\lambda}{d} = 2 \frac{\lambda}{a} $

$\large a = \frac{d}{5} = \frac{1}{5} $

∴ a = 0.2 mm