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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