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!

Ohm's Law: Help please and thank you!

  1. Apr 24, 2009 #1
    1. The problem statement, all variables and given/known data

    A cylindrical copper cable carries a current of 1300 A. There is a potential difference of 1.6 10-2 V between two points on the cable that are 0.38 m apart. What is the radius of the cable?

    I=1300A
    V=1.6e-2 V
    l=0.38m
    rho=1.7e-8(resistivity of copper)
    r=?

    2. Relevant equations
    V=IR
    Where: V=voltage, I=Current, R=Resistance

    R=rho* L/r^2pie
    Where: R= resistance, rho=1.7e-8(resistivity of copper), Length in meters, r=radius
    3. The attempt at a solution

    1. Find Resistance.
    V=IR
    1.6e-2V=1300A*R
    R=1.23E-5 ohms

    then I used:
    R=rho* L/rpie^2
    1.23E-5 ohms=1.7e-8*(0.38m/r^2pie)
    2.09e-13=0.38m/r^2pie
    6.57e-13=0.38m/r^2
    6.57e-13*r^2=0.38m
    5.78e11=r^2
    r=760333.43m

    what do I keep doing wrong??
     
  2. jcsd
  3. Apr 24, 2009 #2

    LowlyPion

    User Avatar
    Homework Helper

    That step is woefully wrong.

    Perhaps if you rewrote it

    r2= 1.7*10-8*(.38)/(π*1.23*10-5)
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook