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What is Airy's discs? |
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Answer» Solution :(i) Similar to a rectangular SLIT, when a circular aperture or opening (like a lens or the iris of our eye) forms an image of a POINT object, the image formed will not be a point buta diffraction pattern of concentric CIRCLES that BECOMES fainter while moving away from the center as shown in Figure. These are known as Airy's discs. `a sin theta = 1.22 lamda`  (ii) Here, the numerical value 1.22 comes for central maximum formed by circular APERTURES. For small angles, `sin theta = theta` `a theta = 1.22 lamda` Rewriting further, `theta = (1.22 lamda)/(a) " and " (r_0)/(f) = (1.22 lamda) / (a)` ` r_0 = (1.22 lamda f)/( a) ` |
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