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Question
Depict the orientation of an electric dipole in (a) stable and (b) unstable equilibrium in an external uniform electric field. Write the potential energy of the dipole in each case.
Solution
- The dipole is in stable equilibrium when it is parallel to the electric field (i.e., the angle between the dipole moment and the electric field is 0°).
- When the dipole is aligned anti-parallel to the electric field (i.e., the angle between the dipole moment and the electric field is 180°, then the dipole is in unstable equilibrium.
For stable equilibrium (θ = 0°)
Potential energy U = -pE cosθ
U = -pE
For unstable equilibrium (θ = 180°)
Potential Energy U = -pE cosθ
U = pE
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