Question

(Fig. 3.95) shows four orientations of an electric dipole in an external electric field. Rank the orientations acording to the
a. magnitude of the torque on the dipole, and
b. potential energy of the dipole, greatest first.
.

Answer 1

For 2 and 4, `tau = p E sin theta, U = -p E cos theta`
For 1 and 3,` tau = p E sin (180 - theta) = p E sin theta`
`U = -p E cos (180 - theta) = p E cos theta`
Hence, torque is same for all, and U is greater for 1 and 3 than 2 and 4.