Electrodynamics

The Alternating Current Generator
(Alternator)

1. Mechanical energy is used to create electrical energy.

2. A coil (loop) is physically (mechanically) turned in the area of a magnetic field.

3. As a result of Faradays Law, an electric current is generated in the loops. There is a change in the magnetic flux linkage through the loops as the coil is rotated.

REMEMBER THAT YOU ARE TURNING THE LOOPS.
SO THE LOOPS ARE ROTATED CONTINUOUSLY IN ONE DIRECTION BY YOU.

4. The RED LOOP is always connected to the RED BRUSH as the loops are rotated round and round. This GREEN LOOP is always connected to the GREEN BRUSH. This is possible due to the SLIP RINGS. The SLIP RINGS ensure that a particular loop is ALWAYS connected to the same BRUSH.

5. Consider the RED LOOP. According to Flemmings Right Hand Dynamo Rule, as you move the RED LOOP upwards, a current is induced forwards, which reaches the RED SLIP RING and enters the RED BRUSH. This current then moves as shown in the external purple wire.

6. But when the RED LOOP reaches the South Magnet Pole, in would be moving downwards.
But the magnetic field direction is still the same. So the RED LOOP is actually now moving downwards in the same magnetic field as before. So current will be induced in the other direction.

7. When the rotation takes the RED LOOP back to the original position, the original current direction will be induced.

8. So, as the RED LOOP is rotated in one direction (which really means UP and DOWN in the same field), CURRENTS IN OPPOSITE DIRECTIONS are induced. This is called ALTERNATING CURRENT.

9. As the loops rotate through the magnetic field, they make different angles with the field. This results in different magnitudes of current being induced.

10. As shown, the current would be maximum. As the loops ascend to reach the top, the current would decrease to zero. Then as the loops continue to rotate (descend), current would be induced in the opposite direction, increasing to a maximum as the loop reaches the South magnet. As it passes the South magnet, the current would then decrease in magnitude.

11. Then the loops starts to ascend from below the magnets. Current is now induced in the original direction, reaching maximum when the loop reaches the North magnet again.

12. This goes on and on! Round (Up) and round (Down).

13. Although the speed of rotation is constant, the magnitude of induced current is not constant. The current increases and decreases as the angle the conductor makes with the magnetic field changes.

14. The two aspects of the induced current, change in direction and change in magnitude can be represented in a graph (sine graph).