How to judge the direction of magnetic field?

Magnetic field direction: specifies the direction of magnetic field force at a certain point in the magnetic field of the north pole of the small magnetic needle as the direction of electromagnetic field.

The direction from the north pole to the south pole is from the south pole to the north pole inside the magnet, which can be expressed as the tangent direction of the magnetic induction line, or as the direction pointed by the north pole when the small magnetic needle is put into the magnetic field at rest!

The north and south poles of the magnetic field are just opposite to the geographical north and south poles, and there is a magnetic declination between the two poles at one end, which is called the magnetic declination! The magnetic declination changes slowly! Mastering the change of magnetic declination is of great significance to the application of compass pointing!

Extended data:

Electrostatic electrons have electrostatic electron mass and unit negative charge, so a gravitational force and a unit negative electric field force are applied to the outside. When an external force accelerates a stationary electron to make it move, the external force not only provides kinetic energy for the whole movement of the electron, but also provides magnetic energy for the magnetic field generated by the moving charge.

It can be seen that the magnetic field is a magnetic energy substance injected by external force into moving electrons through energy conversion. The magnetic field produced by current or negative point charge is a macroscopic manifestation of the magnetic field produced by a large number of moving electrons.

Similar to the electric field, the magnetic field is a vector field distributed continuously in a certain spatial area. The basic physical quantity describing the magnetic field is the magnetic induction intensity vector B, which can also be vividly expressed by magnetic induction lines. However, as a vector field, the nature of magnetic field is very different from that of electric field.

The total magnetic field generated by moving charge or changing electric field, or the sum of the two, is a passive and rotating vector field, and the magnetic lines of force are closed curve clusters, which are uninterrupted and do not cross. In other words, there is no source of magnetic field lines, and there is no tail that converges magnetic field lines. The closure of the magnetic field lines shows that the loop integral along the magnetic field lines is not zero, that is, the magnetic field has a spin field instead of a potential field (conservative field), and there is no scalar function similar to the potential.

In quantum mechanics, scientists believe that pure magnetic field (and pure electric field) is an effect caused by virtual photons. According to the standard model, photons are the medium of all electromagnetic effects. In the low field energy state, this difference can be ignored.

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