Energy of a Dipole in a Constant E Field

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Homework Statement


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?

Homework Equations


U = -pEcos[tex]\theta[/tex]


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!
 

Answers and Replies

  • #2
rl.bhat
Homework Helper
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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.
 
  • #3
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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.

Thank you so much! That really cleared it up for me!
 

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