MAGNETIC FIELD & MAGNETIC FORCES
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.
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.
Opposite poles (N and S)
attract and like
poles (N and N,
or S and S) repel.
These bar magnets will remain "permanent"
happens to eliminate
the alignment of
in the bar of
Fig. 27.1 Bar magnets (permanent magnets)
The Earth's magnetic
to come from
a giant bar
with its south pole located
up near the
Earth's north pole
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
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
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