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(فايق شقران) #1

[CENTER]Magnetic Field

MAGNETIC FIELD & MAGNETIC FORCES
(Chapter 27)

SOURCES OF MAGNETIC FIELD
(Chapter 28) appears below Ch 27

KEY TERMS: permanent magnet, magnetic monopole,
Tesla, Gauss, magnetic field line, magnetic flux, Weber,
mass spectrometer, magnetic dipole moment or
magnetic moment, solenoid, Hall effect.


[SIZE=3]There are no individual magnetic poles
(or magnetic charges). Electric charges can
be separated, but magnetic poles always come in pairs

  • one north and one south. [/size]
    Opposite poles (N and S)
    attract and like
    poles (N and N,
    or S and S) repel.

    These bar magnets will remain "permanent"
    until something
    happens to eliminate
    the alignment of
    atomic magnets
    in the bar of
    iron, nickel,
    or cobalt.

    Fig. 27.1 Bar magnets (permanent magnets)


The Earth’s magnetic
field appears
to come from
a giant bar
magnet, but
with its south pole located
up near the
Earth’s north pole
(near Canada).

The magnetic field lines come out of the Earth
near Antarctica and enter near Canada.

Fig. 27.3 Earth’s magnetic field

The connection between electric current and
magnetic field was first observed when the
presence of a current in a wire near a magnetic compass affected the direction of the compass needle. We now know
that current gives rise
to magnetic fields, just
as electric charge gave
rise to electric fields.

Fig. 27.5 Compass near a current-carrying wire

The direction of the cross product can be obtained
by using a
right-hand rule
:
FINGERS
of the right
hand point in the
direction of the
FIRST
vector (v) in
the cross product, then
adjust your wrist so that
you can bend your
fingers(at the knuckles!) toward the direction of
the second vector (B);
extend the thumb to
get the direction
of the force.

Fig. 27.6 Magnetic force acting on a moving charge


Fig. 27.11 Magnetic field lines of a permanent magnet, cylindrical coil, iron-core electromagnet, straight
current-carrying wire, and a circular
current-carrying loop.



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(zoromba1) #2

جزاك الله عنا خيرا يا اخي