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 do have a definite direction relative to the direction of propagation of the wave. However, in general, there are no specific directions for the oscillations of the electric and magnetic fields they vibrate in any randomly oriented plane perpendicular to the direction of propagation. As noted in the previous chapter on Electromagnetic Waves, EM waves are transverse waves consisting of varying electric and magnetic fields that oscillate perpendicular to the direction of propagation ( Figure 1.33). Light is one type of electromagnetic (EM) wave. (credit a and credit b: modifications of work by “Amithshs”/Wikimedia Commons) Malus’s Law 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. Figure 1.32 These two photographs of a river show the effect of a polarizing filter in reducing glare in light reflected from the surface of water.

Light intensity to force equation