1. Not finding help here? Sign up for a free 30min 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!

Electric Current Help

  1. Jan 18, 2006 #1
    Can anyone help me with this question? Thank-you

    A net charge of 51 mC passes through the cross-sectional area of a wire in 10.0 s. What is the current in the wire? How many electrons pass the cross-sectional area in 1.0 min?

    I know that the current is .0051, but I'm having trouble finding the electrons. I know an amp is a coulomb per second, am I going to use C=6.3e18 somewhere? I tried 6.3e18/60 sec but that was wrong
     
  2. jcsd
  3. Jan 18, 2006 #2

    Doc Al

    User Avatar

    Staff: Mentor

    Hint: The charge on an electron is 1.6e-19 C. (6.25e18 is the number of electrons required to make one Coulomb of charge.) Start by figuring out how much charge (in Coulombs) passes in 1.0 min.
     
  4. Jan 18, 2006 #3
    would i multiply 1.6e-19 C x 60 seconds? I have to use seconds correct?
     
  5. Jan 18, 2006 #4

    Doc Al

    User Avatar

    Staff: Mentor

    No. You found the current (0.0051 A) so use it. Current = charge/time; you have the current and the time: solve for the charge. Then figure out how many electrons equal that charge.
     
  6. Jan 18, 2006 #5
    I get 1.36e-5 for the charge. So is it going to be 1.36e-5/1.6e-19?
     
  7. Jan 18, 2006 #6

    Doc Al

    User Avatar

    Staff: Mentor

    How did you get that value for the charge? (Once you get the correct charge, yes, divide it by the electron charge to find the number of electrons.)
     
  8. Jan 18, 2006 #7
    i divided the current by 60 seconds... .0051/60 then i multiplied it by 1.6e-19 and i got 8.5e-5, but that is wrong what did i do?
     
  9. Jan 18, 2006 #8

    Doc Al

    User Avatar

    Staff: Mentor

    Current = Charge/Time, or...

    Charge = Current x Time.

    (If you keep track of your units, you'll make fewer mistakes.)
     
  10. Jan 18, 2006 #9
    yes... so its going to be current/time=charge and i got 8.5e-5 then i multiplied it by the charge on an electron 8.5e-5 x 1.6e-19 and I got 1.36e-23. Where am i going wrong?
     
  11. Jan 18, 2006 #10

    Doc Al

    User Avatar

    Staff: Mentor

    Nope. Reread what I wrote above.
     
  12. Jan 18, 2006 #11
    my apologies after i multiplied current x time i got 0.306, and then I divide by 1.6e-19? I want to make sure I get this right becausr I am running out my submissions, thank-you for ur time
     
  13. Jan 19, 2006 #12

    Doc Al

    User Avatar

    Staff: Mentor

    Correct. But always attach units to your answers. When you multiplied current by time you got charge, so that answer was 0.306 C. And you will divide by 1.6e-19 C per electron. Your final answer will be just a number (of electrons).
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?