# Questions about magnetics

1. Oct 2, 2012

### klmnopq

1-What's the difference in Magenetic between B,H or in electric between D,E?

2-what's permanent magnet and how it differ from electromagnetic pole?

2. Oct 2, 2012

### cabraham

E is electric field intensity. D is electric flux density, aka electric displacement. If an E field is present in a dielectric, then the external source of E field reduced to zero, the dielectric will retain a state of polarization, called "D". Energy is stored in the dielectric.

A similar scenario takes place with ferromagnetic material. H is the magnetic field intensity. When H is reduced to zero, the ferrous material retains magnetic polarization & energy. The magnetic flux density is "B".

A good e/m fields text goes into detail with the math. I recommend peer-reviewed text books, & university web sites. Avoid web sites not peer reviewed. Many of these sites are kept by people who are just pretenders, wanna be's, hackers, & know-nothings, seeking an audience. They will only confuse you.

Claude

3. Oct 3, 2012

### vanhees71

Good textbooks on electromagnetism are

A. Sommerfeld, Lectures on Theoretical Physics, Vol. III
R. Becker, The classical Theory of Electricity and Magnetism

Although somewhat older they give a very concise treatment of Maxwell's theory, including the relativistic point of view, without which electromagnetism is not understandable and many even newer textbooks get their readers confused when it comes to electromagnetic fields in moving media.

Also very illuminating and more uptodate is volume 2 of the Feynman Lectures.

From the very beginning relativistic and thus very good from a physical point of view is volume 2 of Landau/Lifgarbages's textbooks on theoretical physics. It's perhaps a bit too advanced for undergraduates or beginners in E+M. The same is true for "the bible" on the subject, which is very comprehensive, namely Jackson, Classical Electrodynamics.

A very good book, using very powerful but unconventional mathematical techniques is the textbook by J. Schwinger, Classical Electrodynamics.

4. Oct 3, 2012

### klmnopq

thanks very much for replay
but I wonder what you mean by (aka electric displacement)
and I also haven't understand the difference

thanks very much.
I need not the mathematatical approach ( equations ) I need to sense the meaning of parameters and depth of Electric & magnetic not math....

I need to understand the meaning and physically

what you choose to me to read???

5. Oct 4, 2012

### vanhees71

Then you should read the Feynman Lectures. There also the right interpretation of the macroscopic fields $\vec{D}$ and $\vec{H}$ is given. In the vacuum and generally on the microscopic level of description it doesn't make sense to distinguish between $(\vec{E},\vec{B})$ and $(\vec{D},\vec{H})$. Only because of the somewhat unnatural choice of units in the SI they have different dimension (in fact, even $\vec{E}$ and $\vec{B}$ have different dimension in the SI!), but they are just the one and only electromagnetic field on the microscopic level of description.

In matter $(\vec{D},\vec{H})$ are derived quantities for an effective theory of electromagnetic fields in matter and are valid within the limitations of the applied approximation (which is, from a microscopic point of view linear response theory for appropriately coarse-grained fields and sources (charges and currents, including magnetization if necessary)).

6. Oct 5, 2012

### klmnopq

where can I get this lectures? Have links?

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