Help with Dipoles Homework: Force, Torque Calculation

[cardinal724]

Homework Statement

A point charge Q is distance r from the center of a dipole consisting of charges + and - q separated by distance s. The charge is located in the plane that bisects the dipole. At this instant, what are (a) the force(magnitude and direction) and (b) the magnitude of the torque on the dipole? You can assume r >>s.

Homework Equations

So I know from my textbook that the electric field of a dipole is (-1/4pi(eo) times (qs/r^3).
The torque I know is also pEsin(theta)

The Attempt at a Solution

So I have these equations but I don't know what to do with them since there were no numerical values given.

So for part a I have F= Eq = (-1/4pi(eo)) times (s*q^s/r^3) and for part b I just have T = pEsin(theta). From here I don't know what to do, there's nothing for me to plug in really..

 

[ehild]

The question is the force and torque exerted on the dipole by the charge Q. There is no use of picking up an equation and plug in values blindly. The force you wrote is wrong.
Also, the formula for the torque refers to the torque in a uniform electric field. The electric field is not uniform in this case.

Go back to good old Coulomb's law.


ehild