intensity of incident unpolarized light equation

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 27.41 shows the effect of two polarizing filters on originally 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 27.40).įigure 27.40 A polarizing filter has a polarization axis that acts as a slit passing through electric fields parallel to its direction. 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 27.39). 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. Thus we can think of the electric field arrows as showing the direction of polarization, as in Figure 27.37.įigure 27.38 The transverse oscillations in one rope are in a vertical plane, and those in the other rope are in a horizontal plane.

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 27.37). 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. theta from 0 degree to 90 degree.Figure 27.36 These two photographs of a river show the effect of a polarizing filter in reducing glare in light reflected from the surface of water. On the axes below, sketch a graph of I vs. (1) At which value(s) of theta is I at a maximum? (2) What is I_max, the maximum value of I, in terms of I_0? Explain. (3) Explain conceptually why it makes sense for I to be at a minimum at these value(s) of theta. (1) At which value(s) of theta is I at a minimum? (2) What is the minimum value of I? Explain.

Use this fact to find all theta (where 0 lessthanorequalto theta lessthanorequalto 90 degree) at which I is at a maximum or a minimum. (As always, simplify.) Maximum and minimum values of I occur where dI/d theta = 0. Find an equation for the intensity I of the light after it passes through filter 3, in terms of only I_0 and theta. Finally, the light passes through filter 3, which has its polarization axis at 90 degree relative to the axis of filter 1. which has its polarization axis at an angle theta relative to the axis of filter 1, where 0 lessthanorequalto theta lessthanorequalto 90 degree. Incident unpolarized light of intensity I_0 passes first through polarizing filter 1.

Intensity of incident unpolarized light equation