# Current through a wire help

## Homework Statement

A current of I=8.0A is flowing in a typical extension cord of length L=3.00m. The cord is made of copper wire with diameter d=1.5mm.

The charge of the electron is e=1.6*10^-19C. The resisitivity of copper is $$\rho$$=1.7*10^-8$$\Omega$$ m. The concentration of free electrons in copper is n=8.5*10^28m^-3

## Homework Equations

I honestly have no idea. There's nothing in my book about collisions at all other than saying that's what causes resistance.

## The Attempt at a Solution

Honestly have no idea where to begin... there is literally not a thing about this in my book. It's from an online homework assignment.

tiny-tim
Homework Helper
hi aftershock!

erm what's the question?

hi aftershock!

erm what's the question?

Wow I can't believe I left that part off, sorry.

Find the total number of collisions that all free electrons undergo in one second.

I was able to see the answer and the equation used was something along the lines of m/($$\rho$$ne2)

I have no idea where that came from though.

tiny-tim
Homework Helper
Wow I can't believe I left that part off, sorry.

he he
Find the total number of collisions that all free electrons undergo in one second.

I was able to see the answer and the equation used was something along the lines of m/($$\rho$$ne2)

I have no idea where that came from though.

not something i'm familiar with , but you might get some help from http://en.wikipedia.org/wiki/Classical_and_quantum_conductivity#Classical_conductivity http://en.wikipedia.org/wiki/Drude_model or http://en.wikipedia.org/wiki/Ohm's_Law