Re: More Wireless Power Transmission (fwd)

["Tesla list" <tesla@xxxxxxxxxx>]

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Date: Thu, 04 Oct 2007 21:55:49 -0700
From: Barton B. Anderson <bartb@xxxxxxxxxxxxxxxx>
To: Tesla list <tesla@xxxxxxxxxx>
Subject: Re: More Wireless Power Transmission (fwd)

Hi Jim,

> <>Then inductance is what?
> Jim

Mathmatically, inductance is ultimately the ratio of the magnetic flux 
in comparison to the value of current flowing in the inductor. This can 
be considered the "top level" definition. It is a value that describes 
the ability to induce a potential difference or a voltage.

When current varies within a conductive material (the current must 
actually be in motion), the permeability of the material will cause a 
magnetic field which produces a magnetic flux (imaginary lines 
representing the field density). The density of this field feeds back 
upon the conductor or neighboring conductors. When this occurs, a 
voltage is produced in the conductor or neighboring conductors. So an 
inductor with a varying current can impose upon itself a voltage 
separate from the voltage applied. This "induced" voltage will oppose 
the applied voltage. When this occurs, there is an opposition to the 
flow of current and thus a resistance which occurs. We call this 
resistance the inductive reactance.

So single wires can produce an inductance upon themselves (if current 
varies). Neighboring conductors can be induced if the magnetic field of 
a conductor crosses magnetic paths of other conductors. It's a transfer 
of energy from what we call current to a magnetic field and back to 
current. But there are losses associated with energy transfer. The 
conductor material is obviously part of the equation due to the 
differences in permeability from what we find as a useful material. 
Without inductance, there would be no Tesla Coil. The ability of the 
primary to induce the secondary is what makes the energy transfer possible.

Take a wire and make a circle out of it, and those magnetic imaginary 
lines can cross their own path far denser if close enough. And if there 
are neighboring turns, they all are magnetically coupled to oneanother 
(inductively and capacitively). A coiled winding has greater inductance 
than a wire of the same length which is not coiled (and thus can only 
induce a voltage within itself based on it's geometry and level of the 
magnetic field). You can imagine how geometry of the coil becomes 
important for a particular inductance.

Thanks to Faraday, Neumann, Maxwell, and many people, we can calculate 
the inductance easily. But to understand what is actually going on is 
not something everyone has a good grasp on.

Take care,
Bart