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: Charged rod in your hand stays charged

  1. Jan 20, 2010 #1
    1. The problem statement, all variables and given/known data

    When you rub a rubber rod with fur it becomes negatively charged. How does it keep it's charge if it's in your hand?

    2. Relevant equations

    3. The attempt at a solution

    We did this in the lab and it definitely stays charged (at least long enough to observe some other reactions to it). I don't know why it doesn't lose it's charge into me since I'm holding it
  2. jcsd
  3. Jan 20, 2010 #2


    User Avatar
    Homework Helper

    hi rest_7, welcome to PF.
    Unlike the metal rod, rubber is an insulator, in which charges are localized. They won't conduct through it to your hand to conduct to the ground. Due to this same reason you cannot charge the metal rod by holding it in your hand.
  4. Jan 22, 2010 #3
    Thanks very much for the reply! That makes sense :-) But if it is not a conductor, how come when we brought that charged rubber rod to the pith ball it transferred it's charge to it?

    Thanks again!
  5. Jan 22, 2010 #4


    User Avatar
    Homework Helper

    When you bring a negatively charged rubber rod near an uncharged pith ball, electrons on the pith ball are repelled back due to the repulsive force leaving the surface near the rod positively charged. When you touch the pith ball with the rod, electrons are transferred from the rod to the pith ball.
  6. Jan 27, 2010 #5
    Thanks for your time in helping me out. I guess that's what is confusing me. That the rod cannot transfer the electrons to me (because it's an insulator) but it can transfer those electrons to the pitch balls. Am I missing something?
  7. Jan 27, 2010 #6
    The charges can only go from the surface of the rod, directly to anonther object that's touching the surface. If you swiped the entire surface of the rod with your hands, you could discharge it as well.
  8. Jan 28, 2010 #7
    Fantastic, thanks for all your help!
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook