Question

Write the principle and working of alternating current generator.

Hint:

The key difference between an AC and a DC generator lies in how the current is extracted. AC generators use two separate slip rings, while DC generators use a single split-ring commutator to reverse the connection every half-turn, keeping the current in the external circuit flowing in one direction.

Answer 1

Step 1: Principle of an AC Generator:
The working principle of an AC generator is electromagnetic induction. It states that whenever the magnetic flux linked with a coil changes, an electromotive force (EMF) is induced in the coil. If the coil is part of a closed circuit, this induced EMF drives a current through it.

Step 2: Construction:
An AC generator consists of the following main parts: \begin{itemize} \item Armature Coil (ABCD): A rectangular coil with a large number of turns of insulated copper wire wound on a soft iron core. \item Field Magnets (N, S): Strong permanent magnets or electromagnets that produce a uniform magnetic field. \item Slip Rings (\(R_1, R_2\)): Two hollow metallic rings to which the ends of the armature coil are connected. They rotate along with the coil. \item Brushes (\(B_1, B_2\)): Two flexible carbon brushes that are kept in light contact with the rotating slip rings. They are used to pass the current from the coil to the external circuit. \end{itemize}

Step 3: Working:
\begin{enumerate} \item The armature coil is rotated mechanically in the magnetic field. As it rotates, the angle between the plane of the coil and the magnetic field lines changes continuously. \item This continuous change in orientation causes the magnetic flux (\(\Phi = NBA\cos\theta\)) linked with the coil to change. \item According to Faraday's law of induction, this change in flux induces an EMF in the coil. The direction of the induced current is given by Fleming's Right-Hand Rule. \item First Half Rotation: As the coil rotates, let's say arm AB moves downwards and arm CD moves upwards. The induced current flows from A to B and from C to D. The current flows out through brush \(B_1\) and into the circuit, returning through brush \(B_2\). \item Second Half Rotation: Arm AB now moves upwards, and arm CD moves downwards. The direction of the induced current in the arms reverses (now from B to A and D to C). The current now flows out through brush \(B_2\) and returns through brush \(B_1\). \item Since the direction of the current in the external circuit reverses after every half rotation, an alternating current is produced. The magnitude of the induced EMF is sinusoidal, given by \(\epsilon = \epsilon_0 \sin(\omega t)\). \end{enumerate}