# Deriving Ohm's Law

Joined May 19, 2013
214
So consider a resistor made up of one single, ohmic material.

Thus:
E(x,y,z) = ro(x,y,z) * J(x,y,z) because the material is ohmic

and

ro(x,y,z) = ro = ct because we have one single material.

Thus: E(x,y,z) = ro * J(x,y,z)

If E is uniform, then J is also uniform. But what is the condition for E to be uniform?

Everywhere I see: ''Assuming E to be uniform etc etc.'' when deriving R = ro*L/S

Must the resistor have a uniform cross-sectional area?

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#### Alec_t

Joined Sep 17, 2013
11,406
I've considered it. Now what?