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: Simple electricity hw problem

  1. Jul 13, 2006 #1
    A metal sphere has a charge of +5.0 µC. What is the net charge after 7.0 x 10^13 electrons have been placed on it?

    What I tried was to convert the number of electrons to a charge by multiplying it by (1.6 x 10^-19)..and then adding that to the 5..from which I got 16.2..am I takin the right approach?
  2. jcsd
  3. Jul 13, 2006 #2


    User Avatar
    Staff Emeritus
    Science Advisor

    The metal sphere has a +5 µC charge, which means a deficit of electrons.

    Add to this 7.0 x 1013 electrons, each of which has a charge of -1.6022 x 10-19 C.

    So the total charge of electrons is 7.0 x 1013 * -1.6022 x 10-19. Note that the electron charge is negative.
  4. Jul 13, 2006 #3
    I'm not sure how you got 16.2. Did you take into account the charge of electrons (-)? Also, make sure to check the units of the metal sphere.

    Aw, astronuc, beat me to it :wink:
    Last edited: Jul 13, 2006
  5. Jul 13, 2006 #4
    Ahh..I completely forgot the negative..thanks astronuc
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook