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!

Work Dipole Rotation (21.62)

  1. Oct 2, 2015 #1
    1. The problem statement, all variables and given/known data
    A dipole consists of charges +e and −e separated by 0.57 nm . It is in an electric field 2.6×104 N/C .
    What is the work required to rotate the dipole from being oriented parallel to the field to being antiparallel to the field?

    2. Relevant equations
    PE = (dipole moment)(electric field) ## = 2.37 * 10^{-24}##
    Work = ##W = PE(\cos{\theta_2}-\cos{\theta_1}) ## (From textbook)
    Antiparallel = ##\theta_2 = 180 ##
    Parallel = ##\theta_1 = 0 ##

    3. The attempt at a solution
    When I plugged the numbers for the equation for work I got ## = -4.7 * 10^{-24}## The correct answer is positive. I don't think I made any math mistakes but I can show my work if requested (plugging in numbers) if needed. Thank you very much.
     
  2. jcsd
  3. Oct 2, 2015 #2

    TSny

    User Avatar
    Homework Helper
    Gold Member

    Is this the work done by the electric forces acting on the charges as the dipole rotates or is it the work done by an external agent that rotates the dipole at constant angular speed?
     
  4. Oct 4, 2015 #3
    jodido.png
    I think it's done by the electric field
     
    Last edited: Oct 4, 2015
  5. Oct 4, 2015 #4

    TSny

    User Avatar
    Homework Helper
    Gold Member

    From the textbook's derivation, you can see that they use the torque produced by the electric forces acting on the charges. So, the work they calculate is the work done by the electric forces. But your problem statement is apparently asking for the work required by an external agent, like yourself, to rotate the dipole. To hold the dipole at some angle, you would need to apply a torque that is equal but opposite to the torque due to the electric forces. If you rotate the dipole at a steady rate, your torque is still equal and opposite to the torque due to the electric forces.
     
  6. Oct 4, 2015 #5
    Thank you so much. Now it makes sense!
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted



Similar Discussions: Work Dipole Rotation (21.62)
  1. Rotational Work (Replies: 1)

  2. Rotational Work (Replies: 3)

  3. Rotational Work (Replies: 1)

Loading...