Class 12 Physics
CBSE and UP Board
Wave Optics
Chapter-10 Exercise 10.10
NCERT Solutions for Class 12 Physics Chapter 10 Question-10
Estimate the distance for which ray optics is good approximation for an aperture of 4 mm and wavelength 400 nm.
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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 x 1o-3 m
Wavelength of light, λ = 400 nm = 400 x 10-9 m
ZF = (4 x 1o-3 m)²/(400 x 10-9) = 40m
Therefore, the distance for which the ray optics is a good approximation is 40 m.