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: 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
    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.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook