Question

Estimate the distance for which ray optics is good approximation for an aperture of 4 mm and wavelength 400 nm.

Answer 1

Fresnel’s distance (ZF) is the distance for which the ray optics is a good approximation. It is given by the relation,

Where,
Aperture width, a = 4 mm = 4 ×10⁻³ m
Wavelength of light, λ = 400 nm = 400 × 10⁻⁹ m

Therefore, the distance for which the ray optics is a good approximation is 40 m.