# Please explain - total electic field Ec + En within the coils must be zero

1. Dec 20, 2011

### bksree

Please explain -- total electic field Ec + En within the coils must be zero

Hi
This is from the text University Physics.
In pg. 1035, chap 10, in order to justify the use of Kirchoff's rule to analyze circuits containing inductors it is written :
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 electic field Ec + En within the coils must be zero, even though neither field is individually zero.

The doubt is : Why should En + Ec be zero ?

TIA
sree

2. Dec 20, 2011

### Gordianus

Re: Please explain -- total electic field Ec + En within the coils must be zero

I don't know what En and Ec mean, but I strongly recommend reading Walter Lewin's lecture on induced fem. He addresses the question why the electric field inside a good conductor should be very small.

3. Dec 20, 2011

### bksree

Re: Please explain -- total electic field Ec + En within the coils must be zero

Ec - conservative electric field (Couloumb's law)
En - non conservative electric field (induced field due to change in flux)

4. Dec 21, 2011

### Gordianus

Re: Please explain -- total electic field Ec + En within the coils must be zero

The voltage drop across an inductor, L dI/dt can be large. However, if you try to equal this figure to the integral of the electric along the coil wire you find a small number because, for any finite current, the field inside a good conductor must be very small.
How do you reconcile both points of view?
Walter Lewin shows how L dI/dt equals the integral of the electric field outside the coil.
I strongly suggest that you watch Lewin's lectures; they're free.