# Easy dipole question help

## Homework Statement

Cosnider two dipoles, p1 oriented along z at the origin, and p2 oriented along x at a distance r in the
x - y plane. Given that the torque on a dipole in a field E can be written N = p x E, find the torque on each dipole about its centre.

## Homework Equations

N=pxE , E= (p/4ε∏r^3)[2cosθrhat +sinθhat]

## The Attempt at a Solution

for p1, I thought , since its on the origin , θ=0 , E=(p/2ε∏r^3)rhat

first of all how do I know which direction is rhat in the x-y-z plane is it just in the z direction? , Now to find
torque = px(p/2ε∏r^3)rhat

and since is the centre of dipole r=r/2

what do you guys think ?
Cheers guys

SammyS
Staff Emeritus
Homework Helper
Gold Member

## Homework Statement

Cosnider two dipoles, p1 oriented along z at the origin, and p2 oriented along x at a distance r in the
x - y plane. Given that the torque on a dipole in a field E can be written N = p x E, find the torque on each dipole about its centre.

## Homework Equations

N=pxE , E= (p/4ε∏r^3)[2cosθrhat +sinθhat]

## The Attempt at a Solution

for p1, I thought , since its on the origin , θ=0 , E=(p/2ε∏r^3)rhat
If you are referring the torque on p1 due to p2, then $\hat{r}\$ is $\hat{x}\ .$
first of all how do I know which direction is rhat in the x-y-z plane is it just in the z direction? , Now to find
torque = px(p/2ε∏r^3)rhat

and since is the centre of dipole r=r/2

what do you guys think ?
Cheers guys