“Arago's rotations”的意思、由来-开放百科全书

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Arago's rotations

释义

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Arago's rotations is an observable magnetic phenomenon and effect discovered by François Arago in 1824.

A magnetic needle is freely suspended on a pivot or string, a short distance above a copper disc. If the disk is stationary, the needle aligns itself with the Earth's magnetic field. If the disc is rotated in its own plane, the needle rotates in the same direction as the disc. (The effect decreases as the distance between the magnet and the disk increases.)

Variations:

If the disk is free to rotate with minimal friction, and the needle is rotated above or below it, the disk rotates in the same direction as the needle. (This is easier to observe or measure if the needle is a larger magnet.)
If the needle is not allowed to rotate, its presence retards rotation of the disc. (This is easier to observe or measure if the needle is a larger magnet.)
Other non-magnetic materials having electrical conductivity (non-ferrous metals such as silver, aluminum, or zinc) also produce the effect.
Non-conductive non-magnetic materials (wood, glass, plastic, ice, etc.) do not produce the effect.

Relative motion of the conductor and the magnet induces eddy currents in the conductor, which produce a force or torque that opposes or resists relative motion, or tries to "couple" the objects. The same drag-like force is used in eddy current braking and magnetic damping.

See also

Further reading