What is AC generator? How is an AC generator used to produce an alternating current? Explain with the help of graph between instantaneous emf and time.

An AC generator, also known as an alternator, is a device that converts mechanical energy into electrical energy in the form of alternating current. The basic principle behind the functioning of an AC generator is Faraday's law of electromagnetic induction, which states that a current is induced in a conductor whenever it is placed in a region where the magnetic field changes with time.

Here's a step-by-step explanation of how an AC generator produces an alternating current:

1. The AC generator consists of a coil of wire that is made to rotate in a magnetic field. This rotation ensures that the magnetic field through the coil changes continuously.

2. As the coil rotates, the magnetic field through it changes, which induces an electromotive force (emf) in the coil. This is due to Faraday's law of electromagnetic induction.

3. The direction of the induced emf is given by Lenz's law, which states that the induced emf will always work in a direction to oppose the change causing it. This means that the direction of the induced emf changes as the coil rotates through one complete cycle.

4. The induced emf causes a current to flow in the coil. Since the direction of the induced emf changes with the rotation of the coil, the direction of the current also changes. This is why the current produced by an AC generator is alternating.

The graph between the instantaneous emf (E) and time (t) for an AC generator is a sinusoidal wave. This is because the emf changes sinusoidally with time. When the coil is parallel to the magnetic field, the emf is zero. As the coil rotates and becomes more aligned with the field, the emf increases, reaching a maximum when the coil is perpendicular to the field. As the coil continues to rotate back to a parallel position, the emf decreases back to zero. This process then repeats in the opposite direction, resulting in a sinusoidal wave.