Potential Energy of Dipole In Electric Field

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Electric Dipole In Uniform Electric Field-

 

Before you go through this article, make sure that you have gone through the previous article on Electric Dipole In Uniform Electric Field.

 

We have learnt-

  • Two equal and opposite forces act on the electric dipole in uniform electric field.
  • These two forces form a couple which tries to rotate the dipole in the electric field.
  • The torque experienced by the electric dipole in uniform electric field is given by-

 

 

In this article, we will discuss the potential energy of dipole in a uniform electric field.

 

Potential Energy of Electric Dipole In Uniform Electric Field-

 

Consider an electric dipole is placed in a uniform electric field E with its dipole moment p making an angle θ with the field as shown.

 

Two equal and opposite forces act on the dipole which forms a couple. This couple exerts a torque on the dipole which tries to rotate it in the electric field.

 

 

The torque experienced by the dipole in the uniform electric field is given by-

 

 

If the dipole is rotated through a small angle dθ against the torque acting on it, then the small work done by the external agent is-

 

 

The total work done in rotating the dipole from its orientation making an angle θ1 with the direction of electric field to the angle θ2 will be-

 

 

This work is stored as the potential energy (U) of the dipole. Thus,

 

 

If initially the dipole is oriented  perpendicular to the direction of the electric field (θ1 = 90°) and then brought to some orientation making an angle θ with the field (θ2 = θ), then potential energy of the dipole will be-

 

 

Special Cases-

 

Case-01: Position of Stable Equilibrium-

 

When θ = 0°, U = -pEcos0° = -pE

 

Thus, the potential energy of a dipole is minimum when its dipole moment is parallel to the external field. This is the position of stable equilibrium.

 

Case-02: Position of Zero Energy-

 

When θ = 90°, U = -pEcos90° = 0

 

Thus, the potential energy of a dipole is zero when it is held perpendicular to the external field.

 

Case-03: Position of Unstable Equilibrium-

 

When θ = 180°, U = -pEcos180° = +pE

 

Thus, the potential energy of a dipole is maximum when its dipole moment is anti-parallel to the external field. This is the position of unstable equilibrium.

 

Read the next article on-

Electrical Capacitance

 

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