All Problems

Diffraction of Light

Problem 5.106

A plane light wave with wavelength λ=0.54\lambda=0.54 \mum goes through a thin converging lens with focal length f=50 cmf=50 \mathrm{~cm} and an aperture stop fixed immediately after the lens, and reaches a screen placed at a distance b=75 cmb=75 \mathrm{~cm} from the aperture stop. At what aperture radii has the centre of the diffraction pattern on the screen the maximum illuminance?

Reveal Answer
r=kλfb/(b−f)=0.90k mm, where k=1,3,5,…r=\sqrt{k \lambda f b /(b-f)}=0.90 \sqrt{k} \mathrm{~mm}, \text { where } k=1,3,5, \ldots
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