# Solving Two Point Dipoles - Find Torque of p1 & p2

• Kolahal Bhattacharya
In summary, the problem given by Griffiths involves calculating the torque of two perpendicular point dipoles, p1 and p2, with a distance of r between them. The formula for the torque of a point dipole pointing in the z direction is given, and the solution for p1 can be easily calculated assuming it also points in the z direction. However, for p2, the axes can be rotated and the sum of the torques can be found using the conservation of angular momentum. There is a disagreement on whether rotating the axes will affect the results.
Kolahal Bhattacharya

## Homework Statement

Griffiths offers this problem: two point dipoles p1 and p2 are given.They are r distance away and they are perpendicular.We are asked to find torue of p1 (about p1's centre) due to p2 and vice versa.
Well, the situation is that I knoe it is =p cross E
even I know the formula for a point dipole pointing in the z direction:
E_dip=(1/(4*pi*epsilon))(p/r^3)[2cos(theta) (r^)+sin (theta) (theta^)
where (r^) and (theta^) are the unit vectors in a polar system coincident with the xyz system.
I can surely find the result for 1 part.Assuming p1 points in the z direction,it can be evaluated.What could be done in the second case?

## The Attempt at a Solution

Both torques are equally easy to compute. Just rotate your coordinate system. But you don't even have to. Their sum is the time rate of change of angular momentum, a conserved quantity. Think Newton's third law.

Last edited:
You are WRONG.If I rotate the axes,the relative difference of answers will not be visible.

Kolahal Bhattacharya said:
You are WRONG.If I rotate the axes,the relative difference of answers will not be visible.

Really? I have no idea what you mean to say, but I guess you know best.

## What is a two point dipole?

A two point dipole is a system consisting of two point charges with equal magnitude but opposite signs, separated by a distance d. It is commonly used to model the behavior of polar molecules and can also be used to study the behavior of electric fields.

## What is torque?

Torque is a measure of the rotational force applied to an object. In the context of a two point dipole, it refers to the tendency of the dipole to rotate under the influence of an external electric field.

## How do you find the torque of p1 and p2 in a two point dipole?

The torque of p1 and p2 in a two point dipole can be found using the equation T = p1 x E + p2 x E, where p1 and p2 are the magnitudes of the two point charges and E is the strength of the external electric field.

## What factors affect the torque in a two point dipole?

The torque in a two point dipole is affected by the magnitude of the point charges, the distance between them, and the strength and direction of the external electric field.

## How is the torque of a two point dipole related to its dipole moment?

The torque of a two point dipole is directly proportional to its dipole moment, which is the product of the magnitude of the point charges and the distance between them. This means that a larger dipole moment will result in a larger torque, and vice versa.

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