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In class we have been given an exercise to simulate capacitance, inductance, and resistance without reference to - well, without refernece to much of anything. The resistor is straightforward, likewise the cap - a voltage is created, energy is stored. Now, how about the inductor? Most inductance descriptions I've seen so far involve either a magnet or an iron rod. How does the generated magnetic field in and of itself affect the current?

Thanks much in advance

Joe

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    \$\begingroup\$ Its not obvious to me why your mental model of an inductor does depend on a magnet. If you can say more about that it might help to explain how the usual model is different. \$\endgroup\$ – The Photon Feb 12 '12 at 16:55
  • \$\begingroup\$ By analogy to your capacitance model: current in a loop produces a magnetic field, energy is stored. Since energy is stored, there must have been some work done to store that energy. Therefore a voltage must have been required to develop the current. \$\endgroup\$ – The Photon Feb 12 '12 at 16:58
  • \$\begingroup\$ A simple way to think about inductors is that they give inertia to current. That's not really how the physics works, but it can be a useful mental model of what they do in a circuit. \$\endgroup\$ – Olin Lathrop Feb 12 '12 at 19:42
  • \$\begingroup\$ Simulating inductance, as a lumped model electrical component, doesn't require reference to magnetism. Simulating mutual inductance probably requires some kind of model of magnetism. \$\endgroup\$ – Kaz Feb 20 '14 at 0:09
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likewise the cap - a voltage is created, energy is stored.

I think your best bet is to draw analogues between inductors and capacitors.

The inductor: a current is created, energy is stored.

Capacitor: I = C dV/dt, E = 1/2 CV2, Q = CV

Inductor: V = L dI/dt, E = 1/2 LI2, Φ = LI

In capacitors, charge Q (I integrated over time) is required to raise capacitor voltage.

In inductors, flux Φ (V integrated over time) is required to raise inductor current.

Energy density:

The electric field: energy per unit volume = 1/2 ε E2

The magnetic field: energy per unit volume = 1/2 μ H2

Capacitance of parallel plate capacitor: C = εA/d

Inductance of long solenoid: L = N2 μA/l

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  • \$\begingroup\$ to clarify; If voltage is equivalent to potential energy, the concept of a voltage field in which energy is stored is intuitive. Current, however, is equated to kinetic energy. By definition it looks to me like energy is "escaping." Consequently, how is it said to be "stored"? \$\endgroup\$ – Joe Stavitsky Feb 12 '12 at 22:10
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    \$\begingroup\$ "Current, however, is equated to kinetic energy" -- NO! Both are equivalent to potential energy; energy is stored in the electric and magnetic fields, respectively. There is a vector potential A for magnetic fields (B = curl A); it's less intuitive than the relationship between electric potential and electric fields, but it can be useful for solving certain modeling problems. \$\endgroup\$ – Jason S Feb 12 '12 at 23:56
  • \$\begingroup\$ I would say that the capacitor stores charge, not voltage (that difference in charge creates the voltage), while the inductor stores energy in the magnetic field, that is generated by the flowing charge; ideally, while the current is constant, the magnetic field is static and not consuming power. When you vary the current, the magnetic field gives/takes energy to compensate for the variation. \$\endgroup\$ – clabacchio Feb 13 '12 at 12:45

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