In 1831, Michael Faraday discovered that changing the magnetic flux passing through a conductive circuit induces an electromotive force (EMF), which drives an electric current in a closed loop. This principle—Faraday's Law of Induction—forms the foundation of modern electrical power generation.

An electrical generator converts mechanical energy into electrical energy by continuously rotating a conductor coil within an external magnetic field, generating a continuously varying induced current.

Principles of AC and DC Generators

As the armature coil rotates at a constant angular velocity (ω) inside a uniform magnetic field (B), the magnetic flux passing through the loop varies sinusoidally (Φ = BA cos(ωt)). According to Faraday's Law, the induced EMF (ε) is proportional to the rate of change of flux:

The fundamental structural difference between alternating current (AC) and direct current (DC) generators lies in how current is extracted from the rotating armature to the external circuit:

• AC Generators (Alternators): Use smooth slip rings connected to carbon brushes. As the coil rotates, the current naturally reverses direction every half-rotation, outputting a smooth sinusoidal alternating current.
• DC Generators: Use a split-ring commutator. The split ring reverses the connection to the external circuit every 180° just as the induced voltage changes polarity, converting the internal alternating current into a pulsating direct current in one direction.

Interactive Exploration

Use the interactive PhET simulation below to explore Faraday's Law. Turn on the Voltmeter and Field Lines, then observe how moving the magnet faster or changing its orientation produces a fluctuating current in the coil.