A point charge Q_1 is distance r from the center of a dipole consisting of charges (+-) q_2 separated by distance s. The charge is located in the plane that bisects the dipole. At this instant, assuming r s, what is the magnitude of the torque on the dipole? Express this factor in terms of q_2, Q_1, s, pi, and r.

torque= l*F

Question

A point charge Q_1 is distance r from the center of a dipole consisting of charges (+-) q_2 separated by distance s. The charge is located in the plane that bisects the dipole. At this instant, assuming r >>s, what is the magnitude of the torque on the dipole? Express this factor in terms of q_2, Q_1, s, pi, and r.

torque= l*F

anonymous · Answer

F = $$F=  \frac{ Q_1*q_2*s  }{ 4*\pi*r^3}$$

l = sSin (theta)

anonymous · Answer

Torque on a dipole of moment p in an electric field E is given by their cross product$$\tau =p\times E= pE sin\theta$$Here in the case it is given that$$\theta =90^o$$So $$Sin\theta =1$$$$\tau =p.E$$and the dipole moment p is defined as $$p= s.q$$The electric field in question is of the charge Q at point 'r' away. Plug the expressions of this E  and p (from above) into the formula for torque. It'll give the answer.