Dipole moment of polarized sphere

AI Thread Summary
The discussion focuses on calculating the dipole moment of a polarized sphere with a given polarization vector. The polarization is expressed as P = (ar^2 + b) r̂, indicating that it varies with the radius r. To find the dipole moment, the relationship delta p = ∫ P . dv is utilized, where small volume elements contribute to the total dipole moment. The participants highlight the need to consider the contributions from opposite sides of the sphere, noting that the dipole moments from these elements will have different directions but similar magnitudes. The conversation emphasizes understanding the vector nature of polarization and its implications for calculating the dipole moment.
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Homework Statement



Consider a polarised sphere of radius R the polarization is given by
P vector = (ar^2 + b) r hat = ( ar+ b/r) r vector
Where a and b are constant

Homework Equations



Find the dipole moment of the sphere

The Attempt at a Solution



I knew that P (polarized)= delta p / delta volume
So to find dipole moment
I'll take : delta p = \int p . dv
I have a solution manual written in it that
P.r vector = Q
So the delta p = Q/4 pi r^2
How they got this equ.
Should i use the polarized equ. That given
Im so confused

Help
 
Last edited:
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Is here anyone can help!,,
 
I don't think you need to do any calculation here.

Note that the polarization vector P has a direction that is radially outward at each point of the sphere and the magnitude of P depends only on r.

So, if you consider a small element of volume dV1 at some point in the sphere at a distance r from the center, the dipole moment of that element will be dp1 = P1dV1.

Now consider a second volume element dV2 (same size as dV1) that is at the same distance r from the center but is on the opposite side of the center from dV1. The dipole moment of that element will be dp2 = P2dV2.

How do the magnitudes of dp1 and dp2 compare? How do their directions compare?

What would you get if you add them: dp1 + dp2 = ?
 
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