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: Charges of conducting spheres

  1. Jun 27, 2009 #1
    1. The problem statement, all variables and given/known data
    Figure 21-36 shows four identical conducting spheres that are actually well separated from one another.

    Figure 21-36
    Sphere W (with an initial charge of zero) is touched to sphere A and then they are separated. Next, sphere W is touched to sphere B (with an initial charge of -29e) and then they are separated. Finally, sphere W is touched to sphere C (with an initial charge of +43e), and then they are separated. The final charge on sphere W is +13e. What was the initial charge on sphere A?


    2. Relevant equations

    don't know

    3. The attempt at a solution
    I tried working backwards from the known charge and using the formula Q=.5(q1-q2). I am sure I am missing something simple, but I can not figure this problem out.
     
  2. jcsd
  3. Jun 27, 2009 #2

    LowlyPion

    User Avatar
    Homework Helper

    Welcome to PF.

    Maybe try working forwards? After touching A you know W carries 1/2A.

    You know what B carries, so after touching B you have 1/2(1/2A + (-29))

    So develop the formula for after touching C and knowing the final value, solve for A.
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook




Loading...