Page 11 - 10-phy-15 Electromagnetism
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15. Electromagnetism eLearn.Punjab
In this situation, plane of the loop is
perpendicular to the magnetic field
and the net force on the coil is zero.
So the loop will not continue to turn
because the forces are still up and
down and hence balanced.
How can we make this coil to
rotate continuously? It can be done
by reversing the direction of the
current just as the coil reaches its
vertical position. This reversal of
current will allow the coil to rotate
continuously. To reverse direction
of current, the connection to coil
is made through an arrangement
Fig. 15.9: Working principle of D.C. motor of brushes and a ring that is split
into two halves, called a split ring
commutator (Fig. 15.9). Brushes, which are usually pieces of graphite, make contact with the
commutator and allow current to flow into the loop. As the loop rotates, so does the commutator.
The split ring is arranged so that each half of the commutator changes brushes just as the coil
reaches the vertical position. Changing brushes reverse the current in the loop.
As a result, the direction of the force on each side of the coil is reversed and it continues to rotate. This
process repeats at each half-turn, causing coil
to rotate in the magnetic field continuously.
Do you Know?
Bank credit cards have a magnet Animation 15.7 : electric motor
strips engraved on them. On this Source & Credit : dynamicscience
strip account information of the
user are stored which are read by V: 1.1
the ATM machine.
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