How an electric motor works
A coil of wire carrying a current in a magnetic field tends
to rotate . This is the basis of an electric motor
The current flows in opposite directions along the two sides of the
coil. By Fleming's left-hand rule the forces on the two sides are in
opposite directions : one side is pushed up and the other down
The two forces produce a turning effect (a moment) on the coil, so
it rotates
The split-ring commutator swaps the connections to the coil
every half turn . This reverses the current in the coil each time it
passes the vertical, so the force on each side reverses and the coil keeps
turning in the same direction
The brushes are contacts that press on the commutator, letting
current flow into the rotating coil
The motor turns faster or with more force if the current is
increased, a stronger magnet is used, or the coil has more
turns . Reversing the current or the field reverses the direction of
rotation
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A simple d.c. motor N S the field runs from N to S force UP force DOWN the two forces are in opposite directions, so the coil TURNS split-ring commutator brushes Each side of the coil carries current in the OPPOSITE direction, so by Fleming's left hand rule one side is pushed up and the other down — and the coil rotates. Half a turn later those sides have swapped over, so the current has to reverse to keep the coil turning the same way. That is what the SPLIT-RING COMMUTATOR does: it swaps the contacts every half turn. To make the motor turn faster: a bigger current, a stronger magnetic field, or more turns on the coil. To reverse it: swap the connections to the battery, or turn the magnets round. A simple dc motor: a rectangular coil between the N and S poles of a magnet, the current direction marked on each side, upward force on one side and downward force on the other, a split-ring commutator on the axle with two brushes connected to a cell
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In the full topic
• How an electric motor works• Loudspeakers and headphones (Physics only)Read the free physics topics →