In the given figure the electric field tend to rotate the electric dipole:

CONCEPT:

Electric dipole in a uniform external field:

• We know that when a charge q is placed in electric field E, it experiences a force F, the force is given as,

⇒ F = qE

• So when an electric dipole is placed in the electric field according to the diagram,
• The force on the +q and the -q charge due to the electric field is given as,

⇒ F = qE

• The net force on the electric dipole will be zero.
• The torque on the electric dipole is given as,

⇒ τ = pE.sinθ

Where θ = angle between the dipole and the electric field

• This torque will tend to align the dipole with the electric field.

EXPLANATION:

• When an electric dipole is placed in an external non-uniform electric field then it is shown as,

     -----(1)

In the diagram,

⇒ E = electric field intensity

From figure 1 it is clear that the force on the charge -q will be,

⇒ F1 = qE      -----(1)

Similarly from figure 1, it is clear that the force on the charge +q will be,

⇒ F2 = qE      -----(2)

• The force F1 and F2 will act opposite to each other.
• The force on the charge -q will act opposite to the electric field while the force on the charge +q acts in the direction of the electric field.

• Since both, the forces are not collinear so the torque will act on the dipole which tries to rotate the dipole anticlockwise. Hence, option 2 is correct.