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Wave Optics

Question

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

Solution

Here,
Aperture, a = 4 mm = 4 × 10^-3 m
Wavelength, λ = 400 nm = 400 × 10^-9 m = 4 × 10^-7 m

Ray optics is good approximation upto distances equal to Fresnel's distance (Z_F).
Fresnel's distance is given by,
$Z_{F} = \frac{a^{2}}{λ} = \frac{{(4 \times 10^{- 3})}^{2}}{4 \times 10^{- 7}} = 40 m .$

Some More Questions From Wave Optics Chapter

Let us list some of the factors which could possibly influence the speed of wave propagation:
(i) nature of source.
(ii) direction of propagation.
(iii) motion of source and/or observer.
(iv) wave length.
(v) intensity of the wave.
On which of these factors, if any, does
(a) the speed of light in vacuum,
(b) the speed of light in a medium (say, the glass or water) depend?

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