# Energy of a Dipole in a Constant E Field

1. Sep 7, 2009

### saxyliz

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.

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$$\theta$$

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. Sep 7, 2009

### rl.bhat

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. Sep 7, 2009

### saxyliz

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