How long does it take an electron to travel 150 km on a copper cable?

[goWlfpack]

Homework Statement

A 150 km long high-voltage transmission line 2.0 cm in diameter carries a steady current of 1030 A. If the conductor is copper with a free charge density of 8.9 1028 electrons per cubic meter, how many years does it take one electron to travel the full length of the cable?

Homework Equations

I= nq(vd)A

where A is the area
vd is the drift speed
n is the charge density
and I is the current

The Attempt at a Solution

SO we are solving for the drift speed so i thought this equation would work. i found the area first using surface area of a cylinder 2pir^2+2pirh and i got 18840.0025 because i converted cm and km both to m.
then i plugged everything else in and the answer was wrong
:(

oh yea and i used -1 for the q which is the charge. i assumed -1 b/c they are electrons

 

[olgranpappy]

Homework Statement

A 150 km long high-voltage transmission line 2.0 cm in diameter carries a steady current of 1030 A. If the conductor is copper with a free charge density of 8.9 1028 electrons per cubic meter, how many years does it take one electron to travel the full length of the cable?

Homework Equations

I= nq(vd)A

where A is the area
vd is the drift speed
n is the charge density
and I is the current

The Attempt at a Solution

SO we are solving for the drift speed so i thought this equation would work. i found the area first using surface area of a cylinder 2pir^2+2pirh and i got 18840.0025 because i converted cm and km both to m.
then i plugged everything else in and the answer was wrong
:(

oh yea and i used -1 for the q which is the charge. i assumed -1 b/c they are electrons

wrong area. you want the cross-sectional area only.

 

[goWlfpack]

ok so I am not solving for drift speed, I am slving for delta t... so now the equations I am trying are Q=(nA(x)) q

and then Q=(nAvdt)q

 

[goWlfpack]

ok so now I've got an A of the cross section which is pir^2... i got .001256
so i multiplied that by 8.9*10^28 and then multiplie that by 150000m .. to get the charge. then i divide the charge by the current to get the time.. still wrong though.. any ideas

 

[olgranpappy]

solve for the drift velocity (v). How long does if take for an electron moving at v to travel \delta x=150000m? I.e., what's \delta t in terms of \delta x and v.