Only the component of the EM wave parallel to the axis of a filter is passed.

When the axes are perpendicular, no light is passed by the second. If the second polarizing filter is rotated, only the component of the light parallel to the second filter’s axis is passed. When the axes of the first and second filters are aligned (parallel), then all of the polarized light passed by the first filter is also passed by the second. The first filter polarizes the light along its axis. The direction of polarization of an EM wave is defined to be the direction of its electric field.įigure 6 shows the effect of two polarizing filters on originally unpolarized light. A polarizing filter has a polarization axis that acts as a slit passing through electric fields parallel to its direction.

Since the light is unpolarized, the arrows point in all directions. The bold arrows represent the direction of polarization of the individual waves composing the ray. The slender arrow represents a ray of unpolarized light. The axis of a polarizing filter is the direction along which the filter passes the electric field of an EM wave (see Figure 5). Thinking of the molecules as many slits, analogous to those for the oscillating ropes, we can understand why only light with a specific polarization can get through. Polarizing filters are composed of long molecules aligned in one direction. Polaroid materials, invented by the founder of Polaroid Corporation, Edwin Land, act as a polarizing slit for light, allowing only polarization in one direction to pass through. Such light is said to be unpolarized because it is composed of many waves with all possible directions of polarization. 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.

Intensity of a light wave equation