Coupon Accepted Successfully!


Electromagnetic Radiation

In Section D we discussed the fact that an accelerating charge will shake up the electric field around it. The shaking portion of the electric field breaks off and moves away through space. The phenomenon is called electromagnetic radiation or light. The electric field is perpendicular to the wave direction, so the wave is transverse, and the orientation of the electric field gives the polarization. That is to say, if the electric field points up and down, then we say the light is vertically polarized. In Figure 14-30 a charge Q on a vertical spring moves up and down and generates the wave shown. So the polarization is in the same direction that the charge shakes.

..\art 14 jpg\figure 14-tam.jpg

Figure 14-30

..\art 14 jpg\figure 14-tan.jpg

Figure 14-31


A magnetic field also goes along with the electric field. Although Figure 14-30 does not show the magnetic field, Figure 14-31 shows both fields. The magnetic field is perpendicular to the electric field and to the direction of propagation.
Of course, this is not the full story. These waves of electric and magnetic fields come out as packets, called photons, generally associated with energy transitions within a crystal, molecule, or atom. We will discuss this more fully in Chapter 16.
This chapter is the most difficult of the book. In addition to visualizing the movement of electrons in various materials, you must also learn to visualize electric and magnetic fields, and an electric potential as well.
The electric field relates force to charge. Whenever you read a question involving force and charge, you will probably need to think of the electric field. You should picture arrows (vectors) filling all of space pointing away from positive charges and toward negative ones. Since the electric field is a vector field, the electric field at a point due to several charges is the vector sum of the individual electric fields at that point.
The electric potential is related to energy and charge. When a question mentions energy and charge, you should immediately think of using electric potentials. The work to move a charge from point A to point B is W = q(VBVA). We can find the potential at point A by simply adding the potentials (V = kQ/r) from the charges in the problem.
An electric field is generated by both stationary and moving charges, although we have calculated only the former. A magnetic field is generated only by moving charges and affects only moving charges. Qualitative information can be obtained by the hand rules. The MCAT will not ask for any more detailed information.

Test Your Skills Now!
Take a Quiz now
Reviewer Name