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: Work on a charge inside a Variable Electric Field

  1. Sep 16, 2015 #1
    1. The problem statement, all variables and given/known data
    A variable electric field permeates all space:

    E= (5.04x+ 84.2)x104i where x is in meters and E is in N/C

    How much work is done to move point charge q = 8.03 μC at constant velocity along the x-axis from point A at (3.63 m,0) to (7.67 m,0)? The sign will indicate who does the work.

    NOTE: This requires integration!

    2. Relevant equations

    3. The attempt at a solution

    Are the limits wrong or the integral itself? Any hints would be greatly appreciated!
  2. jcsd
  3. Sep 16, 2015 #2


    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper
    Gold Member
    2017 Award

    You have written the change in potential energy. If the change in potential energy is negative, the work on the charge is positive. Compare with computing the work as the line integral of the force.
  4. Sep 16, 2015 #3
    OK I think I got it. So the mistake was the sign bc ΔU=-W=-∫F*dl , so since I got ΔU=-30J ⇒ W=30J.
  5. Sep 17, 2015 #4

    rude man

    User Avatar
    Homework Helper
    Gold Member

    I think the original answer is correct. The E field imparts a force in the +x direction on the charge so the work done ON the charge is negative.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted