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

Explanation

For `Z_f` distance, ray optics is a good approximation.

`Z _F` =`(a^2)/ λ`

Here, `a`=`4`×`10^−3``m`, `λ`=`5×10^−7m`

`Z_f`= `(5×`10^−7`)`/`(16×`10^−6`)`
=`32m`

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