Estimate the distance for which ray optics is good approximation for an aperture 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 follow these steps:

### Step 1: Identify the given values
- Aperture (a) = 4 mm = \(4 \times 10^{-3}\) m
- Wavelength (\(\lambda\)) = 400 nm = \(400 \times 10^{-9}\) m

### Step 2: Recall the formula for Fresnel's distance
The Fresnel's distance (\(Z_F\)) is given by the formula:
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