But when they enter a denser medium such as glass, speed reduces, and direction changes at the interface of the two media. When it comes to light waves, they are fastest in a vacuum and air. Although refraction of light waves is the most noticeable, other wave forms such as sound and water also experience it. Moreover, this change in direction is because of a change in the speed of the wave or the difference in the densities of the media. Refraction is the redirection of a wave when it passes from one medium to another. In this article, you will learn about the concepts of refraction and diffraction, their differences, and review commonly asked questions about each phenomenon. Moreover, they are important concepts in the field of physics with a variety of applications. We can only see this if the light falls onto a screen and is scattered into our eyes.Refraction refers to the change in direction of a wave, while diffraction is the spreading of waves. These waves overlap and interfere constructively (bright lines) and destructively (dark regions). (a) Light spreads out (diffracts) from each slit because the slits are narrow. Practical Constructive and Destructive Wave Interference: Double slits produce two coherent sources of waves that interfere. It should be noted that this example uses a single, monochromatic wavelength, which is not common in real life a more practical example is shown in. 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.
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