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Image from: General Electric Corp.
Magnetism is a fundamental force of nature, like the force of gravity. Like gravity, which causes objects to be attracted to each other, magnetism causes magnetized objects to be attracted to each other. The force of magnetism comes from the properties of electric charges.
In most cases, planetary magnetic fields are produced by currents of molten metal alloys which circulate deep within a planet.
An example of the force of magnetism at work is the magnet from your kitchen which sticks to the refrigerator door.
On Earth, a simple compass can always be used to detect the presence of the magnetic field of the earth around you, as well as any other nearby magnetic field.
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