inductor. This means that energy can temporarily be stored in an inductor, similar to that of a capacitor.
ELECTROMAGNETIC WAVES Maxwell’s equations put together the facts related to magnetism and electricity into a series of statements and equations that are outlined here: •
Electric field lines start on positive charges and end on negative charges with an electric field defined as a force per unit charge, with the strength of the force related to the permittivity of free space.
•
Magnetic field lines are continuous and have no beginning or end. The strength of the magnetic field is related to the magnetic constant called the permeability of free space.
•
Changing magnetic fields will induce an electromotive force, which creates an electric field. This relates to Lenz’s law, which means that the emf opposes the change in magnetic field.
•
Magnetic fields are generated by moving charges or by changing electric fields so that electric current changes will create magnetism.
What these theories put together is the idea that electric fields and magnetic forces are not separate but are different manifestations of the same thing—which is electromagnetic force. These changing fields will propagate from their source like waves. These are now defined since the time of Maxwell to be EM waves or electromagnetic waves. These waves are capable of exerting a force over great distances from their source. How fast do these waves move? When calculated, it turns out that they move at 3 x 108 meters per second, which is the speed of light. Whenever a current varies, there will be variable electric and magnetic fields that move out from the source like waves. The electric field surrounding the wire is produced by the charge distribution on the wire. The magnetic field B propagates outward as well. Both of these propagate as an electromagnetic wave, such as when a broadcast antenna sends out a signal in a radio or TV station. These waves are similar to other waves we’ve
287
