This Demonstration shows the oscillations of the strengths of the electric and magnetic fields in a part of a plane electromagnetic wave moving through empty space at a fixed time. As you move the slider to the right, the blue and red sinusoidal curves trace out the variations in the electric (blue) and magnetic (red) field strengths as a function of The electric and magnetic fields are in phase, in that the strength of the magnetic field is at maximum when the strength of the electric field is at maximum. The wave is polarized in the direction. The direction of propagation of the wave is perpendicular to the directions in which the field strengths vary.
The variable labeled strength is the electric field strength , in units of V/m. The corresponding magnetic field strength is in units of , where is the speed of light, equal to m/s. The variable labeled frequency could be taken to be a multiple of, for example, a common FM radio wave frequency of Hz, which has a wavelength of 3 m.