The ray bends toward the perpendicular, since the wavelets have a lower speed in the second medium. Huygens’s principle applied to a straight wavefront traveling from one medium to another where its speed is less. The wavelets closer to the left have had time to travel farther, producing a wavefront traveling in the direction shown.įigure 4. As the wavefront strikes the mirror, wavelets are first emitted from the left part of the mirror and then the right. In addition, we will see that Huygens’s principle tells us how and where light rays interfere.įigure 3 shows how a mirror reflects an incoming wave at an angle equal to the incident angle, verifying the law of reflection. We will find it useful not only in describing how light waves propagate, but also in explaining the laws of reflection and refraction. Huygens’s principle works for all types of waves, including water waves, sound waves, and light waves. The new wavefront is a line tangent to the wavelets and is where we would expect the wave to be a time t later. These are drawn at a time t later, so that they have moved a distance s = vt. Each point on the wavefront emits a semicircular wave that moves at the propagation speed v. A wavefront is the long edge that moves, for example, the crest or the trough. The new wavefront is a line tangent to the wavelets.įigure 2 shows how Huygens’s principle is applied. Each point on the wavefront emits a semicircular wavelet that moves a distance. Huygens’s principle applied to a straight wavefront.
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