Question

A number 12 copper wire has a diameter of 2.053 mm. Calculate the resistance of a 31.0 m long piece of such wire.
(Use 1.72×10-8 Ωm for the resistivity of copper.)

---So Far I have
radius r= diam/2;
area A= pi*r^2
R=(density*length given)/area

but how do I get density out of resistivity ?

Answer 1

what are you tlaking about??
its not density.. its resistivity itself LOL..

try to understand.. resistivity is a constant for a material..
\[R \alpha l / A\]

bigger length bigger resistance.. Bigger area.. more space for electrons to move without banding.. and hence lesser resistance..
This is true for any metal..
but now.. the constant is unique for different material... so that constant is called resistivity!! (and not density)

Answer 2

And so How do I solve it?

Answer 3

Plug in the values..
you have diameter which gives you Area
you have the length
you have the resistivity..

Answer 4

so whats the answer

Answer 5

1.61e-1 ohms?