Question

A rifle used for target shooting has a small telescope so that the shooter can accurately aim at his target. Suppose the telescope has a diameter of 1.5 cm and the shooter is looking at two small birds that are 200 m away. Assuming a red light of wavelength 600 nm shining on the birds, calculate how far apart are the birds.

Answer 1

$\theta=\tan \theta=\frac hL=\frac{1.22\lambda}D,$

$h=\frac{1.22\lambda L}D=1~cm.$