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

Explanation

To estimate the distance for which ray optics is a good approximation for an aperture of 4 mm and a wavelength of 400 nm, we can use the concept of the Fresnel distance. The Fresnel distance (Zf) is given by the formula:

\[ Z_f = \frac{a^2}{\lambda} \]

where:
- \( a \) is the size of the aperture,
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