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Homework Help: Electron travel in a wire; distance

  1. Oct 20, 2009 #1
    1. The problem statement, all variables and given/known data
    The starter motor of a car engine draws a current of 140 A from the battery. The copper wire to the motor is 5.0 mm in diameter and 1.2 m long. The starter motor runs for 0.95 s until the car engine starts.

    How far does an electron travel along the wire while the starter motor is on?

    2. Relevant equations
    drift velocity= (j) / (en)
    j= current density, e=elementary charge, n=concentration of gases in material(given in book)

    j= I/A

    3. The attempt at a solution
    I found the charge that passes through the starter motor to be 133 Coulombs. Am I suppose to incorporate the equation for drift velocity in order to find the distance?
  2. jcsd
  3. Oct 20, 2009 #2
    and I actually just found the current density to be 7130141.45 A/m^2 using the second equation.
    now, how am I suppose to go from this to the distance the electron travels after 0.95 seconds??
  4. Nov 15, 2010 #3
    you can use simple mechanics. consider the electron a point charge moving with a uniform drift velocity and i presume you will get the solution. just don't expect me to get it for you though.
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