What Is Gaussmeter?
In 1896, Edwin Herbert Hall discovered
in the process of working on his doctoral thesis that if electrical
current was passed through a thin strip of gold while it was exposed
to a magnetic field, a small but measurable voltage was developed
across this strip at right angles to both the direction of current
and field, proportional to both.
This effect results from the Lorentz
force on moving electrons in a magnetic field, which forces them to
one side of the strip. They build up a charge there until the charge
is just sufficient to counter the effect of the magnetic field.
These devices are known today as
Hall-effect sensors. They are made of semiconductor material, not for
the amplifying effects used in transistors, but merely because such
materials have a high electrical resistance.
The higher resistance forces the
electrons in the current stream to move at a higher speed, which
increases the resulting voltage. A Hall sensor measures magnetic
field strength in a very small region, nearly at a point (a typical
sensor might have an active site on the order of 0.030 in across).
Only the part of the magnetic vector
which is normal (that is, at right angles) to the Hall element is
measured, so the sensor must be oriented in that direction. Most
gaussmeters on the market today use Hall sensors.
A few, however, use some other
principle, such as magnetoresistors, which change their resistance in
a magnetic field; magnetoresonance, a method used in medical MRI
scanners; and, for less accurate devices, mechanical gaussmeters,
which use the attraction of two permeable materials for each other,
against a spring, in the presence of a magnetic field.
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