One day, after pulling down your window shade, you notice that sunlight is passi

Question

One day, after pulling down your window shade, you notice that sunlight is passing through a pinhole in the shade and making a small patch of light on the far wall. Having recently studied optics in your physics class, you're not too surprised to see that the patch of light seems to be a circular diffraction pattern. It appears that the central maximum is about 9cm across, and you estimate that the distance from the window shade to the wall is about 3m .Knowing that the average wavelength of sunlight is about 500 nm, estimate the diameter of the pinhole.

Explanation / Answer

sin(theta) = 1.22*lamda/D

sin(theta) = 9cm/3m = 9/300 = 3/100

3/100 = 1.22*500/D

D is the diameter of the aperature

D = (1.22*500*10^-9)*(100/3) = 2.03*10^-5 m = 20.3 micro m = 0.0203 mm

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