Question

For what distance is ray optics a good approximation when the aperture is $4mm$ wide and the wavelength is $500nm$?

• A. 32 m
• B. 64 m
• C. 16 m
• D. 8 m

Answer 1

Answer: (A)

For $Z_F$ distance ray optics is a good approximation.
$Z_F=\frac{a^2}{\lambda }$
Here, $a=4\times 10^{-3}m,\lambda =5\times 10^{-7}m$
$\therefore Z_f=\frac{16\times 10^{-6}}{5\times 10^{-7}}=32m$