This cancels out any wave and results in no light. Destructive wave interference occurs when waves interfere with each other crest-to-trough (peak-to-valley) and are exactly out of phase with each other. Without diffraction and interference, the light would simply make two lines on the screen.Ĭonstructive and Destructive Wave InterferenceĬonstructive wave interference occurs when waves interfere with each other crest-to-crest (peak-to-peak) or trough-to-trough (valley-to-valley) and the waves are exactly in phase with each other. Young’s Double Slit Experiment: Light is sent through two vertical slits and is diffracted into a pattern of vertical lines spread out horizontally. The pattern that resulted can be seen in. In his experiment, he sent light through two closely spaced vertical slits and observed the resulting pattern on the wall behind them. People did not accept the theory that light was a wave until 1801, when English physicist Thomas Young performed his double-slit experiment. Newton felt that color, interference, and diffraction effects needed a better explanation. But some people disagreed with him, most notably Isaac Newton. As we discussed in the atom about the Huygens principle, Christiaan Huygens proved in 1628 that light was a wave. The double-slit experiment, also called Young’s experiment, shows that matter and energy can display both wave and particle characteristics. Explain why Young’s experiment more credible than Huygens’.The direction of propagation is perpendicular to the wavefront, as shown by the downward-pointing arrows. The tangent to these wavelets shows that the new wavefront has been reflected at an angle equal to the incident angle. The wavelets shown were emitted as each point on the wavefront struck the mirror. Reflection: Huygens’s principle applied to a straight wavefront striking a mirror. The ray bends toward the perpendicular, since the wavelets have a lower speed in the second medium. Huygens’s Refraction: Huygens’s principle applied to a straight wavefront traveling from one medium to another where its speed is less. shows visually how Huygens’s Principle can be used to explain reflection, and shows how it can be applied to refraction. The principle is helpful in describing reflection, refraction and interference. This principle works for all wave types, not just light waves. The new wavefront is tangent to the wavelets. The emitted waves are semicircular, and occur at t, time later. Where s is the distance, v is the propagation speed, and t is time.Įach point on the wavefront emits a wave at speed, v. Sources are said to be coherent when the waves emitting from it have constant phase difference and same frequency.\] The corners or opening through which diffraction takes place also acts as a source. Therefore, sound waves can be diffracted.Īccording to the Huygen’s each point on a wave acts as a source and hence is called secondary wavelets. Owls are able to communicate at long distances due to the fact that their hoots, which have long wavelengths, are able to diffract around forest trees. Some applications of diffraction of sound are. The sound waves diffract around the corners or through door openings as we are able to hear the conversations going on in the next room. When bending around the corners, the sharpness of diffraction increases with increase in wavelength and vice versa. Here, $d$ is the length of the opening or the distance between the slits The mathematical representation of diffraction is given by. It occurs when a wave strikes an opening or an obstacle in its path whose size is comparable to the wavelength of the wave. Waves bend when the obstacle or opening is comparable to the wavelength of the wave.ĭiffraction is the phenomenon which is described as the bending of waves around an obstacle or corner into a region of geometrical shadow. The larger the wavelength, the more the waves bend. Hint: Diffraction is a phenomenon in which waves bend around the corners or openings to spread in a region of geometrical space.
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