Electric & Magnetic Fields at Point P with Dielectric/Magnetic Material

In summary, you say that the electric field at a point P in space in the presence of a dielectric material is the sum of the electric field due to polarization due to the external field and the field due to the dielectric material itself. This is also true of the magnetic field at a point P in space with the addition of the magnetic field due to the dielectric material.
  • #1
yungman
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Electric/magnetic field at point P in presence of dielectric/magnetic material.

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
 
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  • #2


whats your question?
 
  • #3


granpa said:
whats your question?

I just want to verify my assertion. Books are not very clear on this.
 
  • #4


yungman said:
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?
 
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  • #5


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.
 
  • #6


granpa said:
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.
 
  • #7


DrDu said:
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.
 
  • #8


yungman said:
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.
 
  • #9


yungman said:
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.
 
  • #10


DrDu said:
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
 

What are electric and magnetic fields?

Electric and magnetic fields are physical phenomena that are created by the presence of electric charges and magnetic materials. These fields are invisible but can be detected and measured using specialized instruments.

How are electric and magnetic fields related?

Electric and magnetic fields are closely related, as they are both components of the larger electromagnetic field. Changes in one field can create changes in the other, and they are both affected by the properties of the materials they interact with.

What is the difference between electric and magnetic fields?

The main difference between electric and magnetic fields is their source. Electric fields are created by the presence of electric charges, while magnetic fields are created by the movement of electric charges. In addition, electric fields act on electric charges, while magnetic fields act on moving electric charges.

How do dielectric materials affect electric fields?

Dielectric materials are materials that do not conduct electricity. When placed in an electric field, they become polarized, which means that their molecules align themselves with the direction of the field. This results in a change in the strength of the electric field in the material.

How do magnetic materials affect magnetic fields?

Magnetic materials, also known as ferromagnetic materials, have the ability to create their own magnetic fields. When placed in an external magnetic field, these materials become magnetized and can either increase or decrease the strength of the overall magnetic field in the region.

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