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Earth Inductor (Magnetometer)
Alfred L. Robbins-Martin Co., USA, circa 1900
Normally, the spinning coil is used because somebody wants electricity, and the arrangement is called a generator. But sometimes everything else is controlled and the amount of electricity is proportional to the magnetic field. That gives a measuring instrument called a magnetometer. This earth inductor is a simple magnetometer. It shows that you can make electricity from Earth's field. With careful adjustment you can use it to show both the dip and direction of Earth's field (though not nearly as accurately as if you'd used a dip circle or compass). And with a little practice and calculation, you can measure the strength of the Earth's magnetic field as well. A more accurate magnetometer would have a constant-speed motor spinning the coil. That would be a precision instrument called a flip-coil magnetometer. A simple inductor like the one above would be more useful in a physics or geography class. |
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When
a coil of wire spins in a magnetic field, it generates electricity.
The amount of electricity is proportional to the strength of the magnetic
field, the area of the coil, the number of turns of wire in the coil,
and the speed with which it turns. (It can get rather complicated.)