Electric fields in an Inductor

mathsciguy

Let's assume we are dealing with an inductor whose coils have negligible resistance. Then a negligibly small electric field is required to make charge move through the coils, so the total electric field E_c+E_n within the coils must be zero, even though neither of the field is individually zero.

E_n and E_c are the non-conservative and conservative electric field respectively.

I've quoted this from the textbook I'm using (University Physics by Young and Freedman 12th edition).

Now, it seems to me that the author just invoked the assumption that the inductor have negligible resistance and hence it only needs very small electric field (thus approximately zero?) to move the charges through it out of nowhere.

It seems wishy-washy to me, it's very convenient so that we can just advance through the discussion and go ahead with the derivation and come up with a very nice equation. My question is, really, how come the net electric field within an inductor is zero? The proposition that 'the inductor just have a very very small resistance so the electric field is zero' isn't very convincing to me, can anyone expound on this for me?

mfb

Use superconductors if "very small resistance" is not small enough for you. They have zero resistance, and all electric fields have to come from magnetic effects.

mathsciguy

@mfb: Does that mean that I just have to believe that proposition? I mean, if it's an experimental fact, then I don't have any problems with it. I'm just a little irked by how it's presented to me I guess, or most probably I've missed something crucial.

mfb

It is an experimental fact that you can have setups where resistance is negligible (or even zero).
You can have other setups as well, but they are not discussed in your quote.

Enthalpy

Only type I superconductors have zero resistance, but are limited to a few mT. Type II superconductors, which are normally used for coils, have a resistance.

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mfb Mentor	Use superconductors if "very small resistance" is not small enough for you. They have zero resistance, and all electric fields have to come from magnetic effects.

mathsciguy	@mfb: Does that mean that I just have to believe that proposition? I mean, if it's an experimental fact, then I don't have any problems with it. I'm just a little irked by how it's presented to me I guess, or most probably I've missed something crucial.

mfb Mentor	Electric fields in an Inductor It is an experimental fact that you can have setups where resistance is negligible (or even zero). You can have other setups as well, but they are not discussed in your quote.

Enthalpy	Only type I superconductors have zero resistance, but are limited to a few mT. Type II superconductors, which are normally used for coils, have a resistance.