Question

For what distance is ray optics a good approximation when the aperture is 3mm wide and wavelength is 500 nm?

Answer 1

Here, 

a = 3mm 

= 3 × 10⁻³m 

λ = 500 nm 

= 5× 10⁻⁷m 

Fresnel distance, 

Z_F = ?

Z_F = \(\frac{a^2}{\lambda}\) 

= \(\frac{(3\times 10^{-3})^2}{5\times 10^{-7}}\) 

= 18m