An experiment is set up to test the angular resolution of an optical device when red light (wavelength λrλr) shines on an aperture of diameter DD.

Which aperture diameter will give the best resolution?

a. D=0.5λ

b. D=λr

c. D=2λr

Option C ⇒ D=2λr is the correct answer, since it has the largest aperture diameter.

Explanation:

Regarding Rayleigh's criterion, the angular resolution is given as below:

θ = 1.22λ/D

From this expression, it is observed that the larger the aperture size, the smaller will be the value of the angular resolution, and the better the device will be.

This signifies that at very high angular differences, the precision for distinguishing two points is high.

Therefore, option C ⇒ D=2λr is the correct answer, since it has the largest aperture diameter.

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