# Drift velocity of electrons

• cseil

## Homework Statement

There's an engine connected to a battery with a copper wire.
ρ = 1.69x10^-8
n = 8.49*10^28 electrons/m^2

The diameter of the wire is 5mm. The length is 1m.
How long does it take for an electron to go from the battery to the engine if i = 100A?

## Homework Equations

## v_d = \frac{J}{ne} = \frac{i}{Ane} ##

## The Attempt at a Solution

I calculated ##v_d## with the equation I wrote above.
I know that the drift velocity could be considered constant. So I calculated t:

## x(t) = 1m = vt => t = 1/v_d ##

My only question is: why did he give me the resistivity!?
Is there something unclear to me?

Thank you

## Homework Statement

There's an engine connected to a battery with a copper wire.
ρ = 1.69x10^-8
n = 8.49*10^28 electrons/m^2

The diameter of the wire is 5mm. The length is 1m.
How long does it take for an electron to go from the battery to the engine if i = 100A?

## Homework Equations

## v_d = \frac{J}{ne} = \frac{i}{Ane} ##

## The Attempt at a Solution

I calculated ##v_d## with the equation I wrote above.
I know that the drift velocity could be considered constant. So I calculated t:

## x(t) = 1m = vt => t = 1/v_d ##

My only question is: why did he give me the resistivity!?
Is there something unclear to me?

Thank you
Your method is correct. The resistivity was not necessary, but one can calculate the mobility from it, and then the drift velocity from the mobility. As the current was given, that was not necessary.