A (perfect) dipole p is situated a distance z above an infinite grounded conducting plane (Fig. 4.7). The dipole makes an angle θ with the perpendicular to the plane. Find the torque on p. If the dipole is free to rotate, in what orientation will it come to rest?

Reference figure 4.7

Solution 6P

Step 1 of 4:

Consider a grounded conducting plane and above which a dipole is placed at a distance z. The angle between the dipole and the perpendicular axis above the plane is θ. We are going to find the torque experienced by the dipole.

Consider an image dipole is situated at distance 2z from the actual dipole under the plane. The image dipole must have the opposite charges with respect to the charges in the real dipole. The angle is also the same θ.