Tuesday, June 4, 2013
The essence of an electromagnetic (EM) wave is defined by two key parameters: its frequency and the strength (amplitude) of its electric field (E). The strength of the magnetic field (B) is not a 'free variable' - it is given by E/c, where c is the speed of light. Light is just one variety of EM wave. It, like all others, is self-sustaining because the oscillating electric field produces an oscillating magnetic field and vice versa. The relationship between the orientations of these fields and the direction of wave travel is shown below:
Figure 1: EM Wave Field Orientations (courtesy of: astronomy.swin.edu.au)
Here, the wave propagates in the x-direction, the electric field oscillates in the z-direction, and the magnetic field oscillates in the y-direction. The electric and magnetic field vectors are always perpendicular to one another and exist in a plane that is itself perpendicular to the direction of travel of the light wave. If the light wave is headed towards you, then you can be sure that the magnetic field vector is pointing 90 degrees counter-clockwise from that of the electric field.