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Electric field inside a wire 
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#1
May411, 03:09 PM

P: 94

1. The problem statement, all variables and given/known data
Griffiths says in his "Introduction to Electrodynamics" that electric field inside a conductor is 0, but isnide a wire is different from 0. Since wire is also a conductor, how can that be possible? And how to calculate electric field inside a wire? Wire has resistivity [tex]\rho[/tex], radius a and current I trough it. 2. Relevant equations E= 0 inside a conductor; E = [tex]\frac{I\rho}{\pi a^2}[/tex]z (How to calculate this?) 3. The attempt at a solution Have no idea how to start... 


#2
May411, 03:56 PM

HW Helper
P: 2,322

The wire is not a perfect conductor. A perfect conductor has 0 resistivity, which implies no electric field via your second equation.



#3
May411, 04:05 PM

P: 94

Thank you ideasrule for your response. Any idea how to calculate field in a wire and get my second equation?



#4
May411, 04:35 PM

Mentor
P: 41,560

Electric field inside a wire



#5
May411, 04:54 PM

P: 94




#6
May411, 05:03 PM

P: 94

So, the question here arises is under what conditions is electric field inside a conductor zero and when is it nonzero? And why? Griffiths only explains that when we put conductor in an outer electric field, the field inside is still zero, as is zero without outer field. Then if there is current, the field is as in second equation. But he doesn't explain this.



#7
May611, 12:46 PM

P: 431

The basic question you leave unanswered is why does the field become zero inside an ideal conductor.It does not do that instantly.The external field sets charges in motion which,free to move,set up an electric field that exactly cancels the applied field.That takes time although that is measured on the nano scale.
In a wire the charges do not accumulatenecessary for setting up an electric field.The charges keep movingdriftingto set up a current and not a field of their own. If you read good books such as ResnickHalliday it will say that field inside is zero for an ideal ISOLATED conductor. 


#8
May611, 02:56 PM

P: 3,904

I understand about imperfect conductor have longitudinal [B]E/B] and skin effect and all, but not with perfect conductor. 


#9
May611, 03:52 PM

Sci Advisor
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Thanks
P: 26,148

as Doc Al says … 


#10
May611, 03:58 PM

Mentor
P: 41,560

aim1732 gave an excellent answer, which I agree with. (And I apologize to the OP for forgetting about this thread and not giving a more complete answer myself.) To nikolafmf: To get your second equation, think of it as being equivalent to Ohm's law. (Didn't see you sneak in there, tinytim. ) 


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