An electric dipole of dipole moment p is placed in a uniform electric field of intensity E. If the initial and the final angular position of the dipole with respect to the electric field is θ₁ and θ₂ respectively then the amount of work done will be:

CONCEPT:

Electric dipole

• When two equal and opposite charges are placed at a very small distance to each other then this arrangement is called an electric dipole. 
• The electric dipole moment is defined as the product of the magnitude of one charge and the distance between the charges in an electric dipole.

⇒ P = q × 2r    

Where 2r = distance between the two charges

• Work done required to rotate an electric dipole in an external uniform electric field from the angle θ1 to θ2 is given as,

⇒ W = pE(cosθ1 - cosθ2)

Where θ1 and θ2 = initial and the final angle between the dipole and the electric field

EXPLANATION:

• From the above, it is clear that work done required to rotate an electric dipole in an external uniform electric field from the angle θ1 to θ2 is given as,

⇒ W = pE(cosθ1 - cosθ2)

• Hence, option 2 is correct.