![]() ![]() The Sun and many other light sources produce waves that are randomly polarized (see Figure 4). Vertical slits pass vertically polarized waves and block horizontally polarized waves. The first is said to be vertically polarized, and the other is said to be horizontally polarized. The transverse oscillations in one rope are in a vertical plane, and those in the other rope are in a horizontal plane. For EM waves, the direction of the electric field is analogous to the disturbances on the ropes. However, a vertical slit blocks the horizontally polarized waves. If a vertical slit is placed on the first rope, the waves pass through. ![]() Those in the other rope are in a horizontal plane and are horizontally polarized. The oscillations in one rope are in a vertical plane and are said to be vertically polarized. To examine this further, consider the transverse waves in the ropes shown in Figure 3. The electric and magnetic fields are perpendicular to the direction of propagation. An EM wave, such as light, is a transverse wave. Thus we can think of the electric field arrows as showing the direction of polarization, as in Figure 2. For an EM wave, we define the direction of polarization to be the direction parallel to the electric field. (This is not the same type of polarization as that discussed for the separation of charges.) Waves having such a direction are said to be polarized. Polarization is the attribute that a wave’s oscillations have a definite direction relative to the direction of propagation of the wave. There are specific directions for the oscillations of the electric and magnetic fields. ![]() As noted earlier, EM waves are transverse waves consisting of varying electric and magnetic fields that oscillate perpendicular to the direction of propagation (see Figure 2). Light is one type of electromagnetic (EM) wave. Polarizing sunglasses are particularly useful on snow and water. As a result, the reflection of clouds and sky observed in part (a) is not observed in part (b). Part (b) of this figure was taken with a polarizing filter and part (a) was not. These two photographs of a river show the effect of a polarizing filter in reducing glare in light reflected from the surface of water. What is polarization? How is it produced? What are some of its uses? The answers to these questions are related to the wave character of light. Polaroids have this ability because of a wave characteristic of light called polarization. They have a special ability to cut the glare of light reflected from water or glass as shown in the figure below. Polaroid sunglasses are familiar to most of us. Discuss the property of optical activity of certain materials.Earthquakes spread out, so they do less damage the farther they get from the source. Sunlight, for example, can be focused to burn wood. Waves can also be concentrated or spread out. For example, the longer deep-heat ultrasound is applied, the more energy it transfers. ![]() The energy effects of a wave depend on time as well as amplitude. In fact, a wave’s energy is directly proportional to its amplitude squared because Because work \(W\) is related to force multiplied by distance (\(F_x\)) and energy is put into the wave by the work done to create it, the energy in a wave is related to amplitude. The larger the displacement \(x\) the larger the force \(F = kx\) needed to create it. More quantitatively, a wave is a displacement that is resisted by a restoring force. Large ocean breakers churn up the shore more than small ones. Loud sounds have higher pressure amplitudes and come from larger-amplitude source vibrations than soft sounds. Large-amplitude earthquakes produce large ground displacements. The amount of energy in a wave is related to its amplitude. (credit: Petty Officer 2nd Class Candice Villarreal, U.S. The Richter scale rating of earthquakes is related to both their amplitude and the energy they carry. \): The destructive effect of an earthquake is palpable evidence of the energy carried in these waves. ![]()
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