ELECTROMAGNETIC RADIATION!
 

James Clerk Maxwell (1831 - 1879)

According to Maxwell's Equations, if a charge is accelerated, it emits an E field which is at a 90 degree angle to the normal field of a charge. This is called a “radiation field,” and moves outward at the speed of light!


An oscillating charge generates electromagnetic waves!
Heinrich Hertz (1857 - 1894)


Outgoing spherical waves at large distances from the source look like “plane waves.”
Ordinary light sources do not produce waves with E in any particular direction. Thus, in a given wave front, you will find E fields in all possible directions.


These electromagnetic waves are “polarized,” that is, the E and B fields point in specific directions that are the same no matter what part of the wave you inspect.(Sweep your right fingers from E to B and your thumb will point in the direction the wave is travelling.)

Oliver Heaviside (1850 - 1925)

When Maxwell's equations are written in differential form, rather than in the integral form we have seen so far, they naturally combine together to produce classical wave equations for the E and B fields... transverse waves propagating at the speed c of 3 × 108 m/s in vacuum.
From Maxwell's Equations to the Wave Equations!






If you wrote the solution to the wave equation as E(x,t) = Emcos[kx - ωt] then the corresponding B field would be B(x,t) = Bmcos[kx - ωt] where Bm = Em/c. Here k = 2π/λ and ω = ck.

Note that the wavelength λ and frequency f for any electromagnetic wave whatsoever always satisfies f λ = c in vacuum. In matter, the effective speed of an EM wave decreases, and since its frequency is fixed, its wavelength also decreases!


Electromagnetic Spectrum!
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Polarization!