|This apparatus demonstrates one aspect of Michael Faraday's 1820 discovery of electro-magnetic rotation. The bar magnet is pivoted top and bottom, and can rotate freely about its long axis. An electric current enters the magnet halfway down its length by way of a contact between a projecting wire and an annular trough of mercury, and leaves at the bottom through a similar contact. The current travelling down the entire width of the magnet is thus exposed to the magnetic field lines, and experiences a torque, causing the magnet to rotate. This is an illuminating demonstration for students (and others) who think that the field lines must remain stationary with respect to the current-carrying conductor for a magnetic force to be produced.|
How to classify this piece of apparatus? Other examples are shown with the electric motors and others with the apparatus of Daniel Davis, Jr.
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