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Week 3: Magnetic Fields and Static
Electricity
Part 1:
Magnetic Fields
Background
A magnet moved into the
space nears a second magnet, experiences a force as it enters the magnetic
fieldof the second magnet. The magnetic field model is a conceptual way of
consideringhow two magnets interact with one another. The magnetic
field model does not consider the force that one magnet exerts on another one
through a distance. Instead, it considers the condition of space around
a magnet. The condition of space around a magnet is considered to be changed by
the presence of the magnet. Since this region of space, or field, is produced
by a magnet, it is called a magnetic field. A magnetic field can be
represented by magnetic field lines. By convention, magnetic field lines
are drawn to indicate how the north pole of a tiny imaginary magnet
would point when in various places in the magnetic field. Arrowheads indicate
the direction that the north pole would point, thus defining the direction of
the magnetic field. The strength of the magnetic field is greater where the
lines are closer together and weaker where they are further apart. Magnetic
field lines emerge from a magnet at the north pole and enter the magnet at the
south pole. Magnetic field lines always form closed loops.
Magnetic field strength is defined in terms of the
magnetic force exerted on a test charge of a particular charge and velocity.
The magnetic field is thus represented by vectors (symbol B) which
define the field strength, also called the magnetic induction. The units are: