Physics Ncert Solutions Class 12th Physics Class 12th Wave Optics

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

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10.10 Fresnel's distance ( $Z_{F})$ is the distance for which the ray optics is a good approximation. It is given by the relation

$Z_{F} = \frac{a^{2}}{?}$ where $a$ =aperture width = 4 mm = 4 $* 10^{- 3}$ m

$?$ = wave length = 400 nm = 400 $* 10^{- 9}$ m

Hence $Z_{F} = \frac{{4 * 10^{- 3}}^{2}}{400 * 10^{- 9}}$ = 40 m

Therefore, the distance for which ray optics is a good approximation is 40 m.

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

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