Silly EM questions

[daqq]

Hi guys,

I'm having a bit of trouble with some questions on weird EM situations. Specifically:

1. Assume a cylinder* of a dielectric material, where wave propagation speed of light is lower than c. Lets say that it gets hit by an RF pulse (wave paket). Part of the pulse gets reflected, the rest travels through the material. Now let's rotate the cylinder very fast by 180 deg around its axis (which is perpendicular to where the pulse hit the object). The question: Will the RF pulse exit in the direction from which it came (basically will it travel with the mass of the object) or will it merrily travel onward, ignoring the movement of the object?

2. Assume a cylinder with a dipole antenna inside of it. This cylinder rotates at an extreme velocity. In a CW RF field, is there any rate of rotation during which the antenna will have a constant DC voltage on it?**

Thanks,

David

* - arbitrarily chosen shape, can be any 3D shape.
** - the antenna must be encased in something with a lower propagation speed than c, because to get a DC voltage the ends of the antenna would have to travel at c.

[ogden]

1. Assume a cylinder* of a dielectric material, where wave propagation speed of light is lower than c. Lets say that it gets hit by an RF pulse (wave paket). Part of the pulse gets reflected, the rest travels through the material. Now let's rotate the cylinder very fast by 180 deg around its axis (which is perpendicular to where the pulse hit the object). The question: Will the RF pulse exit in the direction from which it came (basically will it travel with the mass of the object) or will it merrily travel onward, ignoring the movement of the object?

You will get your question answered here: https://en.wikipedia.org/wiki/Sagnac_effect

[T3sl4co1l]

2. is the inverse of the spinning dipole emitter.  As such, it is a parametric system, where the EM field couples with the rotational power, and the dipole is merely a polarizer where no power is consumed.

To see that it couples with rotational power, consider if the dipole and the field are at an angle to each other.  Therefore there is a torque upon the dipole.  If this torque remains positive (which it will, if the field and rotor have the same angular frequency), then power is consumed from or delivered to the rotor.

Relativity being what it is, this works equally well for a magnetic bias, too.

Tim

[daqq]

Thanks guys!