# Homework Help: Forces between the dipole and a point charge

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1. Feb 27, 2017

### Albi Mema

1. The problem statement, all variables and given/known data
We have an electric dipole with moment P=2*[10][/-5] pointing in x direction. What is the force experieced by dipole at origin when a point charge Q=3*[10][/-4] is located at (0.014 m ,0,0)

2. Relevant equations
1. [E][/dipole]=(1/4π[ε][/0])(2p/r3)
2. p=qs
3. F=qE
4. τ=pEsinϑ

3. The attempt at a solution

I know that the [E][/dipole] can be calculated by the given formula. Then after that I can find force by F=E*r(distance between dipole center and point charge). The problem is that the point charge is located in the line along x. Does the formula change in this case. My book gives no explanation on the way the formulas are derived even thought I self learned some of them.

2. Feb 27, 2017

### kuruman

Hi Albi Mema and welcome to PF.

If you know about gradients, find the potential energy of the dipole in the field generated by the point charge and take the negative gradient to find the force.
If you don't know about gradients, consider the dipole as consisting of a negative and a positive charge separated by distance d, calculate the sum of the forces on the two charges then find an expression as d → 0.