# Specific resistivity, parallel design, my half baked thought

1. Jan 1, 2006

### Genecks

I was thinking of parallel and series circuits and how they work, but then I began to think more about how I could apply that same knowledge to a wire in terms of resistivity.

I was thinking, well if you add another length piece on, that wouldn't increase electron flow.. that would make it somewhat like a series wouldn't it? But what is the physical effect of adding another piece of wire just to make it longer? that doesn't really do much with resistivity, does it?

Then I thought, well wouldn't making the wire bigger make it like a parallel circuit? but somewhat exponential? from what i understand the electron flow increases, thus the bigger wire might seem like a parallel since greater current can go through...

2. Jan 2, 2006

### phantom_photon

No, since resistivity is an intrinsic property of a material.
Remember that R = pL/A. This is intuitively obvious since having a greater area through which charge may flow means a greater current for a given voltage, hence lower resistance.
Of course any real wire will have a non-zero resistivity, so a certain length of wire could be thought of as a (relatively small) resistor. A series combination of resistors has an effective resistance that is simply the sum of the individual resistances. A parallel combination, on the other hand, has an effective resistance that is smaller than any of the constituent resistors.
So, yes, increasing the radius of the wire would make it like a parallel circuit of two smaller wires, whereas making the wire longer would be like a series circuit.