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Old May 20th 2009, 04:16 PM   #1
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I was going through my study book and in Wave Optics, I came across this sentence regarding Maxwell's theory:
"Light waves are associated with changing electric and magnetic fields. The changing electric and magnetic fields result in propagation of light waves(electromagnetic waves) even in waves."
I didn't actually get it. How does it result in propagation of waves?
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Old May 21st 2009, 09:20 AM   #2
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Consider a dipole antenna connected to an AC generator(or better an oscillator). The AC generator transfers electrons from one limb of the antenna to other limb making one limb positively charged and the other one negatively. Thus a sort of dipole is created. This creates an electric field similer to that due to a dipole. Since AC generator keeps the charge oscillating, the electric field also oscillates. This oscillating or time varying electric field creates a time varying magnetic field ( recall Biot-Savert Law) . Now consider an electric field line of the oscillating dipole. The magnetic field lines will be in the form of closed loops surrounding the electric field lines.( Think how you find the direction of magnetic field of a current carrying wire-by right hand grip rule). These magnetic field lines spread well beyond the location of the electric field lines.

Now this time varying magnetic field creates time varying electric field ( recall Faraday's Law of electromagnetic induction - rate of change of magnetic flux is the emf induced and induced emf causes an electric field). This time varying electric field spreads well beyond the magnetic field line. Thus one field creates the other and the wave is propagated.

Well, this is a very simplified picture but it helps to understand the propagation of wave to certain extent.

Last edited by Parvez; May 21st 2009 at 09:22 AM.
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