Recent content by alephgb

The only reason I'm trying to get a physical picture, in terms of charges moving around and fields is because all of DC circuits is built around Ohms law and this constancy of E within a wire. Once you say that, a lot of physics comes out of it and we know Ohm's law describes these things...

Thanks for the very clear description. It clearly explains why J is constant and if one uses Ohms law, E is constant. I'll try to explain the problem I am having. In each derivation that I have seen one either starts with Ohm's law (J=(sigma)E) and shows that E is a constant or they assume E...

But the reason we can assume the edges are infinitely far apart is because the plates are close together. If we have finite plates then they have to be close together for the field to be approximately constant. I know you know this and we are saying the same thing. However, the wire is not a...

I can see the E field constant for a parallel plate capacitor with no problem because the plates are close together and we assume infinite (effectivly) extent in and plane. I also understand that the field lines are uniform in a uniform wire. However, I cannot get a mental picture where the...

Your explanation is clear and accurate, but let me explanation the difficulty I am having understanding why the electric field is constant in a wire. Textbooks generally describe the parallel plate capacity electric field (when end effects can be neglected) and then describe the wires...

Well thanks anyway. My explanation was purposely oversimplied just to get the idea (yes I know about conduction bands etc.) I thought there should be an explanation of why the electric field is constant from first principles (i.e., by just discussing the charges in the battery and wire and the...

Yea, I know how it works for 1-D and you are mostly right in that the field is constrained to the wire. There is a field outside the wire, but it decays as 1/r^2, so we can ignore it. The question is why does the field stay in the wire as a constant. Let me tell what I think it is. If...

I don't see how holding a constant potential between two surfaces forces the electric field to be constant. Conside a capacitor with two concentric spherical shells held to a constant potential V. The electric field is the same as for a point charge (i.e., inversely proportional to r^2)...

When deriving Ohms law from basic principles (at an introductory physics level) the electric field is always assumed to be constant in a wire (like the electric field between two capacitor plates that are close together). However, a wire may be very long and the distance between the positive...