Electric Generators

An electric generator is a device that converts mechanical energy into electrical energy.

• It works on the principle of electromagnetic induction: when a coil rotates in a magnetic field, an emf (and current) is induced in it.

Principle (Faraday’s Law)

• • Whenever a conductor cuts magnetic field lines, an emf is induced in it.
  • The induced emf is given by:

\(\text{emf} = – \dfrac{d\Phi}{dt}\)

• • \(\Phi = B \cdot A \cdot \cos\theta\) = magnetic flux
  • \(B\) = magnetic field strength
  • \(A\) = area of the coil
  • \(\theta\) = angle between field and coil normal
• The negative sign indicates Lenz’s law (induced emf opposes the change in flux).

Construction of a Simple Generator

• Armature (coil): A rectangular coil of wire rotated in a magnetic field.
• Magnet: Provides uniform magnetic field.
• Slip rings (for AC): Provide continuous connection between the rotating coil and external circuit.
• Split-ring commutator (for DC): Reverses connections every half turn to produce unidirectional current.
• Brushes: Conduct current from coil to the external circuit.

Working of a Generator

• As the coil rotates → it cuts through magnetic field lines.
• This changes the magnetic flux linked with the coil → induces emf according to Faraday’s law.
• The direction of current is given by Fleming’s Right-Hand Rule.

 Types of Generators

• AC Generator: Uses slip rings → output is alternating current.
• DC Generator: Uses split-ring commutator → output is direct current.

Factors Affecting Induced emf

• Speed of rotation of the coil
• Strength of magnetic field (\(B\))
• Number of turns in the coil (\(N\))
• Area of the coil (\(A\))

Applications of Generators

• Power stations (hydroelectric, thermal, nuclear, wind)
• Portable generators for backup power
• Bicycles dynamos for lights