Question

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

• A. 22 m
• B. 32 m
• C. 42 m
• D. 52 m

Answer 1

The correct option is B 32 m

Given:

Aperture Width $a=4$mm

Fresnel distance, $Z_F=\frac{a^2}{\lambda }=\frac{(4\times {10}^{-3}{)}^2}{500\times {10}^{-9}}$
$\therefore z_p=32m$