The a.c. generator

The key components are:

1. Rotating Coil (Armature): A coil of wire that rotates within a magnetic field. Its rotation induces an electromotive force (e.m.f.).
2. Magnetic Field: Provided by a permanent magnet or electromagnet, which provides the magnetic flux that the coil cuts through.
3. Slip Rings: Conductive rings connected to the ends of the rotating coil. They rotate with the coil.
4. Brushes: Stationary conductors (often made of carbon) that maintain contact with the slip rings. They allow the current generated in the coil to be transferred to the external circuit.

The slip rings ensure continuous electrical contact between the rotating coil and the external circuit as the coil rotates, allowing an alternating current to flow.

1. To maintain electrical contact with the rotating slip rings.
2. To allow the alternating current generated in the coil to be transmitted to the external circuit.

The graph should be a sinusoidal wave. Peaks occur when the coil is moving perpendicular to the magnetic field (vertical), resulting in maximum rate of change of flux linkage. Troughs are also when the coil is vertical, but with the opposite polarity. Zeros occur when the coil is parallel (horizontal) to the magnetic field, resulting in minimum rate of change of flux linkage. The X-axis represents time and the Y-axis represents e.m.f. (Voltage). The graph should show one full wave.

The induced e.m.f. is zero when the coil is parallel to the magnetic field. This is because at these positions, the rate of change of magnetic flux linkage is zero. The coil is moving parallel to the magnetic field lines, not cutting across them, so no e.m.f is generated.