Question

what is the motion of electric dipole in a uniform electric field when it is parallel to the field,perpendicular to the field

Answer 1

consider a dipole with charges q and -q in a uniform electric field of intensity E,aligned at an angle theta to the direction of the field.the length of the dipole is 2a

then both charges wil experience force qE in the opp directions.

the 2 forces r equal n opp.so the net force on the on the dipole is zero (therefore the dipole moment wil not experience a translation motion.but a torque acts on the dipole and it produces a turning effect.

torque = (magnitude of one force) x perpendicular distance b/w the forces.

torque = F x d

torque = (Eq) x 2a x sin theta

torque = Ep sin theta (qx2a=p..the dipole moment.)

speical cases.

case 1)if the dipole is pallarel or anti parallel to the field,then theta=0 or 180 degres.

torque = Ep sin 0=0 (min)

case 2)if the dipole is perpendicular to the field,then theta =90 degree.

torque = Ep sin 90=Ep (max)

wen the dipole is parallel to the field i.e.0 degree,the torque is zero then the dipole is in stable equilibrium.

wen the dipole is antiparallel to the field,then also the torque is zero,but the diole is in unstable equilibrium.

in a non uniform electric field,the net force is not zero.so the dipole has translational as well as rotational motions

hope this wil help ya fella...wish u luck!!