Question

An electric dipole is free to move ina uniform electric field. explain its motion when it is placed parallel to the electric field & perpendicular to the electric field

Answer 1

When the dipole is placed parallel to the electric field then there will be no motion because then \[\sin 0 degrees = 0\] so there will be no motion in the dipole.
When the dipole is placed perpendicular to the electric field , then there will be a torque produced and the dipole will constantly cover half a rotation and then turn back .This process will continue.
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Answer 2

1.Since the charges are opposite,we are sure that the net force acting on the dipole is zero,whatever may be the position. So, the center of mass does not move.
2.Now we have to think about torque. If O is the angle made by dipole, then t=pEsin(O)
where p=dipole moment,E=intensity of electric field,t-torque.
3.Hence,if dipole is parallel-no torque
perpendicular-it performs a periodic rotating motion.