InterviewSolution
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InterviewSolution
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A point source of light with wavelength `lambda = 0.50mu m` is located at a disatnce `a = 100cm` in front of a diaphragm with round aperture of radius `r = 1.0 mm`. Find the distance `b` between the diaphragm and the observation point for which the number of Fresnel zones in the aperture equals `k = 3`. |
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Answer» By definition `r_(k)^(2) = k(ab lambda)/(a + b)` for the periphery of the `K^(th)` zone. Then `ar_(k)^(2) + br_(k)^(2) = kab lambda` So `b = (ar_(k)^(2))/(ka lambda - r_(k)^(2)) = (ar^(2))/(ka lambda - r^(2)) = 2` metre. on putting the values.(It is given that `r = r_(k))` for `k = 3`. |
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