Resistivity.

[lord loh.]

Does resistivity depend on the thickness of the wire? I had a derrivation in my class about strain guages where we considered dp/dS - change in resistivity due to change in strain?

 

[Nigel Goodwin]

Does resistivity depend on the thickness of the wire?

Yes, of course it does - the thicker the wire, the lower it's resistance (assuming the material is the same). Think of it like resistors in parallel, adding a second resistor in parallel will half the resistance - likewise doubling the cross sectional area of a wire will half it's resistance, just like using two wires.

 

[Optikon]

Does resistivity depend on the thickness of the wire?

Yes, of course it does - the thicker the wire, the lower it's resistance (assuming the material is the same). Think of it like resistors in parallel, adding a second resistor in parallel will half the resistance - likewise doubling the cross sectional area of a wire will half it's resistance, just like using two wires.

I dont think thats what he asked? The resistivity is the per unit area resistance of a given material. For example, the resistivity of copper is the same whether or not I make a wire of any thickness or a sheet of it.

However, if I add impurities to the copper, it's resistivity changes.

So, I think the answer to his question is NO. Resistivity (in a uniform material) is, by definition, independent of geometery such as a smaller diamter piece of wire.

 

[lord loh.]

If you are right Optikon, why does the strain guage resistance-length derrivatin hace a term of dp/dS

p - rho (resistivity)
S - Strain Guage.

I am still confused. :?