1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Resistivity and Ohm's Law question

  1. Jul 28, 2012 #1
    1. The problem statement, all variables and given/known data
    A long wire connected to the terminals of a 12V battery has 6.4 x 1019 electrons passing a cross section of wire each second. calculate it's resistance.

    answer is 1.2Ω

    2. Relevant equations
    q = ne
    q = IE
    R=ρ L/A

    3. The attempt at a solution
    V= 12v
    n= 6.4 x 1019 electrons

    First I used the number of electrons to find my charge (q)
    q = ne
    q = (6.4 x 1019) ( 9 x 10-31)
    q = 5.76 x 10 -11

    Then calculating my current
    I= Q/T
    Im assuming T is 1s, because it says "passing a cross section of wire each second"
    I = 5.76 x 10 -11/ 1
    I= 5.76 x 10 -11

    Then i calculated my resistance
    R= V/R
    R= 12/5.76 x 10 -11
    R= 2.0 x 1011

    What am i doing wrong? D:
  2. jcsd
  3. Jul 28, 2012 #2


    User Avatar
    Homework Helper

    The charge of an electron is e=1.6(10-19) C.
  4. Jul 28, 2012 #3

    Simon Bridge

    User Avatar
    Science Advisor
    Homework Helper

    ... that would be the electron mass.

    e=1.60217646×10-19 Coulombs
  5. Jul 28, 2012 #4
    LOL! CRAP! i knew that~ :) Thank you :3 I was going insane for a bit.
  6. Jul 29, 2012 #5

    Simon Bridge

    User Avatar
    Science Advisor
    Homework Helper

    Happens to the best of us :-)
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook