# Tesla coils / Toroidal inductor flux

1. Aug 6, 2011

### elegysix

I've been reading up on tesla's wireless power transmission lately, and I've been wondering how magnetic flux through the center of a toroid induces a voltage in its coils. From what I understand, the time derivative of magnetic flux through a loop is proportional to the induced voltage, however; in this case, the coils will be parallel to a field passing through the center of the toroid - meaning no flux through any of the coils.

But what I've read about these toroid inductors suggests that there is an induced voltage. Could someone explain this?

Also, how does the induced voltage compare to that of a solenoid with an equal number of turns? i.e. is the toroid more efficient / effective?

thanks!

2. Aug 7, 2011

### cragar

Are you talking about a toroidal transformer? Well the changing magnetic field will create an E field that is in the direction of the current. What is creating your B field? And what direction is it.

3. Aug 7, 2011

### elegysix

here's a picture of what I mean.
I don't mean to have two sets of coils as in a transformer, but a single set of coils around the loop.
The B field could be from whatever... lets just suppose I'm moving a magnet around, outside the loop.

4. Aug 7, 2011

### cragar

If your moving the magnet, the free electrons in the coil will experience a Lorentz force.

5. Aug 8, 2011

### elegysix

Is there no simple relation like with a solenoid, where emf=N*d(Phi)/dt and Phi is the magnetic flux through the toroid?

6. Aug 8, 2011

### cragar

you can calculate it with Faraday's law but i was just giving you a physical picture. when you move the magnet they move because of the Lorentz force not because of an induced E field.

Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook