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: Calculating work done by an electric field

  1. Sep 7, 2008 #1

    crh

    User Avatar

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

    How much work does the electric field do in moving a proton from a point with a potential of +155V to a point where it is -75V. Express your answer in both joules and electron volts.

    2. Relevant equations

    W = -qV

    3. The attempt at a solution

    I know that q=(1.6E-19) but I am not for sure how to go about incorporating my two potentials. Can someone give me some help? I thank you in advance!
     
  2. jcsd
  3. Sep 7, 2008 #2

    Hootenanny

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Perhaps it would help if the equation was written thus:

    [tex]W = -q\Delta V[/tex]

    In other words, the work done by the electric field on the charged particle is the negative product of the charge and the change in potential.
     
  4. Sep 7, 2008 #3

    crh

    User Avatar

    Ok I think I figured it out. Tell me if I am wrong.

    W = -qV, but V is potential E (PE), so therefore V = (PE2-PE1)

    so...

    W = -(1.60E-19C)(-80V) = 1.28E-17 J
    and
    = -(1e)(-80V) = 80eV

    did I go about this right?
     
  5. Sep 7, 2008 #4

    Hootenanny

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    You're on the right lines but be careful when calculating the change in potential.
     
  6. Sep 7, 2008 #5

    crh

    User Avatar

    Are you meaning scientific notation?
     
  7. Sep 7, 2008 #6

    Hootenanny

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Nope, something somewhat simpler than that. What is the difference between -75 and +155?
     
  8. Sep 7, 2008 #7

    crh

    User Avatar

    oh it needs to be -230V.
     
  9. Sep 7, 2008 #8

    Hootenanny

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Much better :approve:
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook