These are like rays that start out in phase and head in all directions. According to Huygens’s principle, every part of the wave front in the slit emits wavelets, as we discussed in The Nature of Light. We then consider light propagating onwards from different parts of the same slit. Here, the light arrives at the slit, illuminating it uniformly and is in phase across its width. The analysis of single-slit diffraction is illustrated in Figure 4.4. (b) The diagram shows the bright central maximum, and the dimmer and thinner maxima on either side. The central maximum is six times higher than shown. (a) Monochromatic light passing through a single slit has a central maximum and many smaller and dimmer maxima on either side. In contrast, a diffraction grating ( Diffraction Gratings) produces evenly spaced lines that dim slowly on either side of the center.įigure 4.3 Single-slit diffraction pattern. Note that the central maximum is larger than maxima on either side and that the intensity decreases rapidly on either side. Figure 4.3 shows a single-slit diffraction pattern. Light passing through a single slit forms a diffraction pattern somewhat different from those formed by double slits or diffraction gratings, which we discussed in the chapter on interference. For example, if you place your middle and index fingers close together and look through the opening at a light bulb, you can see a rather clear diffraction pattern, consisting of light and dark lines running parallel to your fingers. However, situations do occur in which apertures are small enough that the diffraction of light is observable. Since the wavelengths of visible light range from approximately 390 to 770 nm, most objects do not diffract light significantly. The diffraction of sound waves is apparent to us because wavelengths in the audible region are approximately the same size as the objects they encounter, a condition that must be satisfied if diffraction effects are to be observed easily. (credit: modification of map data from Google Earth) If we consider that there are N Huygens sources across the slit shown in (Figure), with each source separated by a distance D/N from its adjacent neighbors, the path difference between waves from adjacent sources reaching the arbitrary point P on the screen is This distance is equivalent to a phase difference of The phasor diagram for the waves arriving at the point whose angular position is is shown in (Figure).Figure 4.2 Because of the diffraction of waves, ocean waves entering through an opening in a breakwater can spread throughout the bay. To calculate the intensity of the diffraction pattern, we follow the phasor method used for calculations with ac circuits in Alternating-Current Circuits. Calculate the intensity relative to the central maximum of an arbitrary point on the screen.Calculate the intensity relative to the central maximum of the single-slit diffraction peaks.By the end of this section, you will be able to:
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