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: Electric forces and fields

  1. Jan 27, 2009 #1
    Please Help!!! Weve just started Physics II and Im lost already. We have been studying Electric forces and fields and now my homework is due tonight by 11pm and I cant even answerer the first question. I thought this would be an easy chapter since there werent many formulas but Im stumped!. This seems like an easy question but I have 5 attempts to get it right and now I've used 4. I must be way off. Well here it goes.

    A plate carries a charge of -3.3 uC while a rod acarries a charge of +2.3 uC. How many electrons must be transferred from the plate to the rod so that both objects have the same charge?

    Well I thought it would be .5 because it would take that many for them to have the same charge but with opp signs. I don't know what formula....doesnt seem like you need one. So far the only one I have is N=q/e
  2. jcsd
  3. Jan 27, 2009 #2


    Staff: Mentor

    If you transfer .5 uC then the plate will have a charge of -2.8 uC and the rod will have 1.8 uC, so they will not have the same charge. Once you determine the correct amount of charge to transfer (q) then you use the equation you cited to determine the number of electrons required (N).
  4. Jan 27, 2009 #3
    well for them to have the same charge... would you have to transfer 3.4 uC from the plate to the rod? Then the plate would have a +.1uC charge and the plate would have +5.7uC charge. It doesnt say same numerical quantity just charge. Or am I just reading the problem incorectly?
  5. Jan 27, 2009 #4
    hey i got it...i dont know what i was thinking. i would transfer 2.8 from the plate and then divide by e giving me 1.75 E 13 electrons.....thanks for the direction .....
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook