For what distance is ray optics a good approximation when the aperture is 2 mm wide and the wavelength is 400 nm?
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → 10 m
Aperture width a = 2 mm
Fresnel distance $z_f =\frac{a^2}{\lambda}$
$=\frac{\left(2 \times 10^{-3}\right)^2}{400 \times 10^{-9}}=\frac{4 \times 10^{-6}}{400 \times 10^{-9}}$
= 10 m