Electric Flux Density / Electric Field Intensity

[zaydana]

Hey people,

I'm struggling to understand exactly what Electric Flux Density D and Electric Field Intensity E are.

So far, my understanding is that D depends on relative permittivity, while E depends only on the permittivity of free space. Also, I understand that D reflects only the free charges, while E reflects both free and bound charges. Where I'm stuck though, is that my book also tells me that D is independent of the medium it is in, while E is dependent on the medium it is in. This just doesn't click with me, since the actual value of E doesn't change if you change the medium (and thus the relative permittivity), while the value of D does.

Can anyone help me out here?

 

[Born2bwire]

The vector quantity B is not the electric flux density, it is the magnetic flux density (or magnetic field depending upon your reference). D is the electric flux density and is related to the electric field by

$$\mathbf{D} = \epsilon \mathbf{E}$$

The boundary conditions for D and E are different. For example, the tangential E field is continuous across a boundary but the normal E field is discontinuous. The normal D across the boundary differs by the charge density that accumulates on the boundary so if we assume no bound charges then the normal D field is continuous, but the normal E field is still discontinuous if there is a change int he permittivity.

So both the D and E fields can change between media depending upon the properties of the media but most cases will assume that no charges will build up on the interface and thus the D field can be continuous in more cases.

 

[astrokreng]

Electric flux density (D) and electric field intensity (E) are two important concepts in the study of electricity and electromagnetism. They both relate to the strength and distribution of electric fields, but they have some key differences.

Firstly, D is a measure of the amount of electric flux passing through a given area. It is directly proportional to the number of electric field lines passing through that area. On the other hand, E is a measure of the strength of the electric field at a given point. It is the force per unit charge experienced by a test charge placed at that point.

Secondly, D and E have different units. D is measured in coulombs per square meter (C/m^2), while E is measured in volts per meter (V/m).

As you mentioned, D is dependent on the relative permittivity of the medium, while E is dependent only on the permittivity of free space. This is because D takes into account the effect of all charges (both free and bound) in the medium, while E only considers the effect of free charges. Bound charges are those that are held in place by the atoms or molecules of the medium, and they do not contribute to the electric field outside of the medium.

This leads to the difference in how D and E are affected by the medium they are in. D is independent of the medium because it takes into account the effect of all charges, regardless of the medium. However, E is dependent on the medium because it only considers the effect of free charges, which may vary depending on the medium.

In summary, D and E are related but distinct concepts that help us understand the strength and distribution of electric fields. D is a measure of the amount of electric flux passing through a given area, while E is a measure of the strength of the electric field at a given point. They have different units and are affected differently by the medium they are in. I hope this helps clarify your understanding of these concepts.