# Mutual inductance as a psuedo-capacitor?

1. Oct 14, 2009

### DMcG

Mutual inductance as a psuedo-capacitor???

1. I am testing how reduced the mutual inductance btwn two parallel ring-shaped inductors is when a material is placed btwn them. The primary coil is connected to an AC generator in series with an ammeter (on the order of mA), and the secondary in series with an ammeter.
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What I'm trying to do is calculate either the permittivity of the material, it's dielectric constant, or some ratio of them, by measuring the reduction in current thru the secondary. [/b]

2. I may have a solution to determining the ratio of epsilon/kappa by the equation epsilonnaught = epsilon / kappa:

3. The primary inductor L1 directs a B-field through the coils of L2, the strength of the field along the axis of the inductor is (munaught / 4 pi) [(2pi*R^2*I)/(x^2 + R^2)^3/2].
But I see elements of a parallell-plate capacitor btwn these coils:[/b]
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The primary current is alternating, but at a given time t the current dq1/dt will possess q1 charges involved in inducting the current dq2/dt, and the secondary will possess q2 charge, which must be less than q1. There should be a potential difference btwn this charge difference, and by the electromagnetic eqn E = -grad(V) there is an electric field pointing along the same axis as the gradient of this potential difference. [/b]
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Now a parallel-plate capacitor has a charge difference and so it also possesses a potential difference and has a (ideally) uniform electric field through it's seperation distance. So if I CAN treat my mutual inductors as a cap, THEN I can use cap-like equations. By the duality relationship btwn inductance and capacitance, the work stored in the electric field of a cap is equal to the work stored in the magnetic field of an inductor: [/b]
(1/2)(L I^2) = (1/2)(C V^2) [/b]
Now V = E*d, where d is sepeartion btwn inductors. [/b]
Also, E = Q /(A*epsilonnaught) [/b]
My prof doesnt really trust my logic on this one. Any help?

2. Oct 14, 2009

### marcusl

Re: Mutual inductance as a psuedo-capacitor???

1) This post doesn't belong in Advanced Physics; Electrical Engineering might be more appropriate.
2) To DMcG: I think you are quite confused about capacitance, inductance, and the differences between electric and magnetic materials. You generally can't treat mutual inductance like capacitance. Visit the following sites for some introductory material on these topics:

Elementary:
http://www.tpub.com/neets/book2/2.htm"
http://www.tpub.com/neets/book2/3.htm"

Wikipedia:
http://en.wikipedia.org/wiki/Inductance" [Broken]
and http://en.wikipedia.org/wiki/Capacitance" [Broken]

http://hyperphysics.phy-astr.gsu.edu/hbase/hframe.html" [Broken]
Click on *inductance on the index to the right, then the Inductance Concepts link. Clicking on the resulting balloons will take you through the various topics. Repeat for *capacitor.

Come back with questions and we'll do our best to answer them.

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