Electric or magnetic field at point P in presence of dielectric/magnetic material.

yungman

I want to confirm either the electric field at a point P in space in an [itex]\vec E_{ext} [/itex] field with the presence of a dielectric material is the sum of the [itex]\vec E_{ext} [/itex] and electric field [itex]\vec E_{p} [/itex] from the dielectric material due to polarization cause by the [itex]\vec E_{ext} [/itex].

And this is also true of the magnetic field at a point P in space with [itex]\vec B_{ext} [/itex] and magnetic material.

Thanks

*granpa*

whats your question?

yungman

Quote by granpa

whats your question?

I just want to verify my assertion. Books are not very clear on this.

*granpa*

Quote by yungman

I want to confirm either the electric field at a point P in space in an [itex]\vec E_{ext} [/itex] field with the presence of a dielectric material is the sum of the [itex]\vec E_{ext} [/itex] and electric field [itex]\vec E_{p} [/itex] from the dielectric material due to polarization cause by the [itex]\vec E_{ext} [/itex]

And this is also true of the magnetic field at a point P in space with [itex]\vec B_{ext} [/itex] and magnetic material.

Thanks

you are asking if the field due to the polarization due to the external field itself causes secondary polarization?

DrDu

Yes, yungman, that's true, at least for the electric field and/ or in magnetostatics. In full electrodynamics, there is also a contribution of the change of P to the magnetic field. In fact, in optics one sets often M=0, so that all effects of the medium are due to P alone.

yungman

Quote by granpa

you are asking if the field due to the polarization due to the external field itself causes secondary polarization?

No, I just want to verify that the field experienced at a point P with a piece of dielectric material close by, is the sum of the [itex] \vec E_{ext} + \vec E_{P} [/itex] where [itex] \vec E_{P} [/itex] is the field from polarizing of the dielectric sitting somewhere in space( somewhere close to P but not touching P).

Same as in the case of magnetic with a piece of magnetic material close by.

yungman

Quote by DrDu

Yes, yungman, that's true, at least for the electric field and/ or in magnetostatics. In full electrodynamics, there is also a contribution of the change of P to the magnetic field. In fact, in optics one sets often M=0, so that all effects of the medium are due to P alone.

Thanks

Do you mean if P is at some conducting material where very small free current density [itex]\vec J_{free}[/itex] created by even static magnetic field. But if P is just a point in space ( empty space) there should be no more changes.

Meir Achuz

Quote by yungman

I want to confirm either the electric field at a point P in space in an [itex]\vec E_{ext} [/itex] field with the presence of a dielectric material is the sum of the [itex]\vec E_{ext} [/itex] and electric field [itex]\vec E_{p} [/itex] from the dielectric material due to polarization cause by the [itex]\vec E_{ext} [/itex].

And this is also true of the magnetic field at a point P in space with [itex]\vec B_{ext} [/itex] and magnetic material.

Thanks

Yes to both cases, but the polarization need not be "caused" by the field. In ferro cases, there mayi not even be an external field.

DrDu

Quote by yungman

Thanks

Do you mean if P is at some conducting material where very small free current density [itex]\vec J_{free}[/itex] created by even static magnetic field. But if P is just a point in space ( empty space) there should be no more changes.

I don't know what you mean with P being just a point in space. In the simplest cases, P corresponds to a dipole density and, e.g. a rotating dipole will lead to a magnetic field. Hence the [tex] \partial P/\partial t [/tex] term on the rhs of Ampere's law.

yungman

Quote by DrDu

I don't know what you mean with P being just a point in space. In the simplest cases, P corresponds to a dipole density and, e.g. a rotating dipole will lead to a magnetic field. Hence the [tex] \partial P/\partial t [/tex] term on the rhs of Ampere's law.

What I meant P is just a reference point in space. It is like books always talk about fields experienced at a point from a source some distance away.

Anyway, thanks for all the replies to confirm my understanding.

Alan

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DrDu Recognitions: Science Advisor	Yes, yungman, that's true, at least for the electric field and/ or in magnetostatics. In full electrodynamics, there is also a contribution of the change of P to the magnetic field. In fact, in optics one sets often M=0, so that all effects of the medium are due to P alone.