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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-what's permanent magnet and how it differ from electromagnetic pole?
thanks very much for replaycabraham said: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 textbooks, & university web sites. Avoid web sites not peer reviewed. Many of these sites are kept by people who are just pretenders, want to be's, hackers, & know-nothings, seeking an audience. They will only confuse you.
Claude
thanks very much.vanhees71 said: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.
Magnets work by creating a magnetic field around them. This field is made up of invisible lines of force that extend from the north pole of the magnet to the south pole. When two magnets are brought close together, the opposite poles attract each other while the same poles repel each other.
Magnets have three main properties: polarity, attraction and repulsion, and the ability to influence other magnets. Polarity refers to the north and south poles of a magnet, while attraction and repulsion are the forces between magnets. Magnets can also be used to attract or repel other magnets or certain metals.
There are three main types of magnets: permanent magnets, temporary magnets, and electromagnets. Permanent magnets, such as refrigerator magnets, retain their magnetism even after being removed from a magnetic field. Temporary magnets, like paperclips, only exhibit magnetism when in a magnetic field. Electromagnets, like those used in motors, are created by passing an electric current through a coil of wire.
Magnets are used in a variety of everyday objects, such as speakers, credit cards, and hard drives. They are also used in medical imaging machines, like MRI scanners, to produce detailed images of the body. Magnets are also used in industrial settings for lifting and moving heavy objects.
Magnets have a minimal impact on the environment as they are a naturally occurring mineral. However, magnets can affect certain electronic devices, such as pacemakers, and should be kept a safe distance away. When disposed of properly, magnets can be recycled and reused in new products, reducing waste and their impact on the environment.