Question

Two perfect dipoles, p1 and p2, are separated by a distance r.

Calculate the torque that p1 exerts on p2. What is the direction and direction of this torque?

Calculate the interaction energy between dipoles p1 and p2.

P1 is perpendicular to the distance "r" and also p2 is perpendicular, but they are in contrary directions

Answer 1

Torque is moment of force.

Torque τ= F× R

Dipole is product of equal and opposite charge.

The electric dipole moment is given as:

p=qd

(Where q is the magnitude of charge and d is the separation distance.)

Electric dipole placed in electric field is given as:

Torque= qd Esinθ

Torque = -pEsinθ

Torque = -p×E (cross product of p and E)

Direction of dipole moment is from positive to negative charge.

Now,

τ₁ = p₁ ˣ Esinθ

τ₂= p₂ ˣ Esinθ

θ= 90°.

Effective dipole moment= √ p₁² + p₂² +p₁p₂cosθ =p

Torque= pEsinθ

=pE*1 =pE

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