1. Not finding help here? Sign up for a free 30min 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!

Calculate the work needed to move a test charge from point B to D

  1. Aug 2, 2012 #1
    Calculate the work needed too move a 1.5μC test charge from point B to D.
    physics5.jpg

    Can someone just check if I'm thinking correctly?

    Do I just use the formula:

    W = qEd ?

    For the E, I calculate the magnitude and direction of the electric field at B.
    And I use 25cm for the distance and q = 1.5μC
     
  2. jcsd
  3. Aug 2, 2012 #2

    TSny

    User Avatar
    Homework Helper
    Gold Member

    W = qEd only works (pun?) if E is uniform. Instead, relate the work to electric potential or electric potential energy.
     
  4. Aug 2, 2012 #3
    Ohhh, I see. So basically, the work needed to bring 1.5μC from a distance (25cm) away to a point 25cm from a charge 75μC?

    Would it make sense to use this formula?


    W = q(Va - Vb)
    W = q[(k*Qa/ra) - (k*Qb/rb)]

    q = 1.5μC
    Qa = 75μC
    Qb = 1.5μC

    ra(75μC to D) = 25cm
    rb(B to D) = 25cm
     
  5. Aug 2, 2012 #4

    TSny

    User Avatar
    Homework Helper
    Gold Member

    That's more like it. But, since the charge is being carried from B to D, you'll need to find the potential difference in going from B to D. How would you find the potential at point B due to the two 75 μC charges? Point D?
     
  6. Aug 2, 2012 #5
    ohhh, righttt.

    So, rewriting it ..

    W = q(VD - VB)

    VD = VD1 + VD2

    VB = VB1 + VB2

    where the distance for VD is 25cm
    and the distance for VB is 35cm
     
  7. Aug 2, 2012 #6

    TSny

    User Avatar
    Homework Helper
    Gold Member

    Yes, Good!
     
  8. Aug 2, 2012 #7
    oh, thank goodness lol! Thank youu!
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Calculate the work needed to move a test charge from point B to D
Loading...