CP80 and CP80 Plus Service Manual 2-17
Magnetic Media
Magnetic media (stripe material) contains small magnetic particles. Before
information is encoded on the stripe, the poles of the magnetic particles are
randomly oriented (top image below). To encode information, the poles of the
individual particles are oriented in the same direction (middle image below). The
effect of having all of the small particles oriented in the same direction is the
same as having one large magnet with a single north pole and single south pole
(bottom image below).
Electrical Current and Magnetism
There is an interrelationship between magnetic fields and electrical current.
When an electrical current moves through a wire, a magnetic field is generated
around the wire
2
. Reciprocally, when a magnetic field moves past a wire, a
current
3
will be generated (induced) in the wire.
Note that in the case of magnetic stripe cards, a static (non-changing) magnetic
field is physically moving past the conductor. This would be analogous to flying
over the mountains in an airplane. The hills and valleys make the distance
between the airplane and the ground increase and decrease, but the landscape
itself does not change.
If the magnetic field (landscape) were changing, the result would be the same,
and induction would occur. What is important is that the magnetic field is either
changing or moving for induction to occur.
2 From Ampere's Law.
3 Mathematically, Faraday's Law of Induction states that a voltage is induced in the conductor. However, for reasons
of symmetry with Ampere's Law, it is common practice in discussion to refer to the energy transfer as "induced
current." This is appropriate as long as the conductor forms a closed circuit and Ohm's Law can be applied.
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