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Homework Help please

  1. Mar 3, 2008 #1
    Homework Help!!! please

    1. The problem statement, all variables and given/known data
    Two problems:

    1. A Van de Graff machine has an electric field of 2000 N/C at a distance of .3 meters. What electrostatic potential energy would a proton have there?
    2. How long would a 3 Farad capacitor light a 60 Watt bulb?


    2. Relevant equations

    Capacitor = Q/V

    3. The attempt at a solution

    I dont know where to start and solve those problems, I need help
     
  2. jcsd
  3. Mar 3, 2008 #2
    2.
    It is easy if the question also has a voltage or you can assume it to be something like mains (240V UK).

    C = Q/V(1), we also know that P = IV(2) and Q = IT(3)

    Rearrange (2) to get it in the form I = P/V and then substitute into (3) Gives...
    Q=(PT)/V. (4)

    Now rearrange (1) to give Q=CV and substitute into (4) This Gives...
    CV=(PT)/V or (CV^2)/P = T

    1. - It's too late/early for me to start thinking about it.
     
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