Construct a simple DC motor and show its working.

Construction: A simple DC motor consists of:

•two magnets one having its north pole facing the south pole of other

•one armature coil (ABCD)

•two split rings (half rings)

•two carbon brushes

•dc supply.

1. The magnets are placed so to produce uniform magnetic field inside the region between them.

2. The two ends of the coil are connected to two split rings which are supported by carbon brushes as shown above.

3. The two carbon brushes are then connected to dc supply with connecting wires.

4. The setup including armature coil and split rings is pivoted onto a rotational axis.

Working:

1. Initially the rotating coil is in horizontal alignment and the magnetic field is always in direction N→S.

2. When the circuit is closed the current start flowing, taking positive charge in account, initially the current is flowing in direction A→B, B→C, C→D.

3. By applying Fleming’s left-hand rule to arm AB where current is in perpendicular direction to present magnetic field, we get that AB experiences force downwards. Similarly arm CD suffers an upward force. So, the coil start rotating in clockwise direction.

4. At instant when the plane of coil is perpendicular to plane of magnetic field the slip rings changes their contact with carbon brush (Slip ring which was connected to left carbon brush get connected to right one and vice versa). Due to this current flows from A→B in arm AB and from D→C in arm CD.

5. Now, by Fleming’s left-hand rule AB suffers upward force and CD suffers downward force but, still coil rotating in clockwise direction.

6. This happens for the next half cycle when again the plane of coil is perpendicular to the direction of magnetic field. The direction of current reverses.

7. The process continues and coil rotates continuously.