Refraction of waves involves a change in the direction of waves as they pass from one medium to another. Reflection involves a change in direction of waves when they bounce off a barrier. Reflection of waves off of curved surfaces will be discussed in more detail in Unit 13 of The Physics Classroom. After passing through the focal point, the waves spread out through the water. It is as though all the energy being carried by the water waves is converged at a single point - the point is known as the focal point. Upon reflection off the parabolic barrier, the water waves will change direction and head towards a point. Several wavefronts are approaching the barrier the ray is drawn for these wavefronts. The diagram at the right depicts such a parabolic barrier in the ripple tank. But what if the surface is curved, perhaps in the shape of a parabola? What generalizations can be made for the reflection of water waves off parabolic surfaces? Suppose that a rubber tube having the shape of a parabola is placed within the water. The discussion above pertains to the reflection of waves off of straight surfaces. This law will be discussed in more detail in Unit 13 of The Physics Classroom. Regardless of the angle at which the wavefronts approach the barrier, one general law of reflection holds true: the waves will always reflect in such a way that the angle at which they approach the barrier equals the angle at which they reflect off the barrier. The diagram below shows the reflected wavefronts and the reflected ray. Upon reaching the barrier placed within the water, these waves bounce off the water and head in a different direction. The blue arrow is called a ray and is drawn perpendicular to the wavefronts. The direction that these wavefronts (straight-line crests) are traveling through the water is represented by the blue arrow.
#Diffraction waves series#
The diagram at the right depicts a series of straight waves approaching a long barrier extending at an angle across the tank of water. These waves will travel through the water until they encounter an obstacle - such as the wall of the tank or an object placed within the water. As viewed on the sheet of paper below the tank, the crests are the dark lines stretching across the paper and the troughs are the bright lines. These straight waves have alternating crests and troughs. If a linear object attached to an oscillator bobs back and forth within the water, it becomes a source of straight waves. Ripple tank demonstrations are commonly done in a Physics class in order to discuss the principles underlying the reflection, refraction, and diffraction of waves. As the waves encounter obstacles in their path, their behavior can be observed by watching the movement of the dark and bright spots on the sheet of paper. As the water waves move through the ripple tank, the dark and bright spots move as well. So the bright spots represent wave troughs and the dark spots represent wave crests. A crest of water will absorb more light than a trough. A portion of light is absorbed by the water as it passes through the tank. A light typically shines upon the water from above and illuminates a white sheet of paper placed directly below the tank. A ripple tank is a large glass-bottomed tank of water that is used to study the behavior of water waves. The study of waves in two dimensions is often done using a ripple tank. But what if the wave is traveling in a two-dimensional medium such as a water wave traveling through ocean water? Or what if the wave is traveling in a three-dimensional medium such as a sound wave or a light wave traveling through air? What types of behaviors can be expected of such two- and three-dimensional waves? Specifically, there will be some reflection off the boundary and some transmission into the new medium. Rather, a wave will undergo certain behaviors when it encounters the end of the medium. The wave doesn't just stop when it reaches the end of the medium. Previously in Lesson 3, the behavior of waves traveling along a rope from a more dense medium to a less dense medium (and vice versa) was discussed.
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