Q.Draw a properly labelled diagram showing the main components of an AC generator. OR What are Eddy currents? How can they be minimised? (1+1=2)

An AC generator converts mechanical (rotational) energy into electrical energy by electromagnetic induction -- a coil rotating in a magnetic field, connected to the external circuit via slip rings and brushes. In the alternative, eddy currents are unwanted induced currents inside the bulk of a conductor, reduced by laminating the core.

Main components of an AC generator

1. Armature (coil) — a rectangular coil $ABCD$ of many turns, wound on a soft-iron core, mechanically rotated.
2. Field magnet — a strong permanent magnet or electromagnet providing a uniform field $B$ (pole pieces N, S) between which the armature rotates.
3. Slip rings — two rings $R_1,R_2$ fixed to (and rotating with) the two ends of the armature coil.
4. Brushes — two stationary carbon brushes $B_1,B_2$ pressing against the slip rings, leading the induced current to the external circuit.
5. Axle/shaft — connects the armature to the external source of rotation (e.g. a turbine).

(Layout: coil $ABCD$ sits between the N and S poles with its rotation axis perpendicular to $\vec B$; each end connects to its own slip ring; the two brushes rub the two rings and connect to the external load $R$.)

Working

As the coil rotates with angular velocity $\omega$ in field $B$, the linked flux varies as $\phi=NBA\cos\omega t$, inducing

$e = -\frac{d\phi}{dt} = NBA\omega\sin\omega t = e_0\sin\omega t$

with peak emf $e_0=NBA\omega$. This sinusoidal emf drives the current delivered through the brushes and slip rings.

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