Estimate the distance for which ray optics is good approximation for an aperture of 4 mm and wavelength 400 nm.
Fresnel’s distance (Zf ) is the distance for which the ray optics is a good approximation. It is given by the relation, Zf = a2/λ
Where,
Aperture width, a = 4 mm = 4 ×10 -3 m
Wavelength of light, λ = 400 nm = 400 × 10 -9 m
Zf = (4x10-3)2/400x10-9 = 40 m
Therefore, the distance for which the ray optics is a good approximation is 40 m.
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