Page 11 - 10-phy-15 Electromagnetism

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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