Single Slit Diffraction A ray passing through the center of the slit will have a path length exactly λ /2 greater than that from the source at A , and hence these two waves will interfere destructively. Now consider a point adjacent to A ; the light emitted with have a path difference exactly λ /2 different to light from a point just above the central point, and will cancel it out. Similarly, for every point between A and the center, there will be a corresponding point λ /2 away between the center and B that will destructively interfere with it. Hence there is effectively no light emitted it the direction θ m and it corresponds to a minimum. A similar situation arises when the path difference between A and B is any whole number of wavelengths--such a situation is shown in , iv). On the other hand, when the path difference between A and B is a half-integer multiple of the wavelength, such as in iii), there will only be partial cancellation. All the emitters between A and a point one-
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