# Given localized moving charge density ρ(X,t), determine electric and m

1. Apr 5, 2014

### Spinnor

Suppose we have two co-linear strings under tension, attached far away, and with propagation speed v. Let the strings have equal and opposite linear charge densities. In each hand you hold an end of a string. With the two strings held close, your hands quickly separate and then come back together again. Such action will produce a wave of charge polarization that moves with speed v away from you. Sketch roughly the electric and magnetic fields of the polarization pulse near the pulse. As v << c, c the speed of light explain why the electric field energy density is much greater than the magnetic field energy density.

Now assume the strings have a propagation speed of c the velocity of light, and assume that the physical pulse height is very small with the linear charge densities increased to compensate for the smaller amplitude. Sketch roughly the electric and magnetic fields of a linear polarization pulse moving away from you at light speed.

If we had the right density of a swarm of linear polarization pulses (both up and down) moving mostly in phase and away from a source could the resultant fields of many polarization pulses approximate that of a beamed antenna? Imagine many pairs of such strings above with pulses.

Is the following close for the first case?

Thanks for any help!

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Last edited: Apr 5, 2014