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Energy of a Dipole in a Constant E Field

  1. Sep 7, 2009 #1
    1. The problem statement, all variables and given/known data
    The graph shows the potential energy of an electric dipole which is in a constant electric field; only the electric force is acting on the dipole. Consider a dipole that oscillates between plus and minus 65 degrees.

    knight_Figure_29_10.jpg

    a) What is the dipole's mechanical energy?
    b) What is the dipole's kinetic energy when it is aligned with the electric field?

    2. Relevant equations
    U = -pEcos[tex]\theta[/tex]


    3. The attempt at a solution
    I know that when the graph is at the trough it's -pE and at it's peak it's +pE. But I don't know how to factor in the 65 degrees. Please help!
     
  2. jcsd
  3. Sep 7, 2009 #2

    rl.bhat

    User Avatar
    Homework Helper

    At 180 degrees U = 2 μJ. Substitute in the relevant equation and find pE.
    At θ = 0, all the potential energy in converted to K.E. Similarly you can find P.E. at 65 degrees by substituting the value of pE and θ in the equation.
     
  4. Sep 7, 2009 #3
    Thank you so much! That really cleared it up for me!
     
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