Magnetic field
The magnetic field is the second component of the electromagnetic field and is
described by the vector of the magnetic induction B (known also as: magnetic
field strength or magnetic flux density) that is perpendicular to the vector of the
electric intensity E . The magnetic field acts only on moving charges and
manifests itself via electromagnetic force FM acting upon flowing currents inside
the region where the magnetic field is distributed. From the Laplace’s law it is
known that the electromagnetic force FM acting upon cable with electric current
i ∙ l that is inside magnetic field with magnetic induction B is equal to the vector
product of the two vectors:
(26) FM = i ∙ 7 × B
(27) dFM = i ∙ dl × B
If we have magnetic dipole the direction of the vector of the magnetic induction is
from the south pole (S) to the north pole (N) inside the dipole and from N to S
outside the dipole.
The magnetic field could be excited either via changes in existing electric field E
or by flowing electric current i .
In the first case the magnetic induction is defined by the Ampere’s law (J=0):
(28)
<f 7 ∙ dl =εo μo
Γ
d Φ E
~dt~
In the second case if we have cable with current i it will generate magnetic field
with induction B whose lines have the direction of rotation of right-handed screw
when it penetrates in the direction of the current i .
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