Electromagnetic Induction & Generators Summary

Electromagnetic Induction

  • Production of electric current/voltage due to relative motion between a conductor and magnetic field.

  • Induced EMF depends on:

    • Number of turns in a coil.
    • Speed of motion of magnet/coil.
    • Presence of soft iron core.
    • Length of conductor.

Laws of Electromagnetic Induction

  • Faraday's Law: Induced EMF/current is proportional to the rate of change of magnetic flux through the coil.
    • E \propto \frac{d\phi}{dt}
    • For N turns: E = -N \frac{d\phi}{dt}
    • E is measured in volts (V).

Lenz's Law

  • The induced EMF always gives rise to a current whose magnetic field opposes the original change in magnetic flux.

Induced EMF in a Straight Conductor

  • When a straight conductor moves through a magnetic field, an EMF is induced between its ends.

  • E = BLV

    • Where:
      • B = flux density
      • L = length of conductor
      • V = velocity

  • If the conductor cuts through the flux at an angle θ:

    • E = BLV \sin{\theta}

  • Maximum EMF is generated when the conductor moves at right angles to the field (\theta = 90°).

  • Direction determined by Fleming's right-hand rule.

Generator

  • A machine that converts mechanical energy into electrical energy based on Faraday's law.

AC Generators (Alternators)

  • Converts mechanical energy into alternating current electrical energy.

  • Works on Faraday's law: EMF/voltage is generated in a current-carrying conductor that cuts a uniform magnetic field.

Parts of an AC Generator:

  • Field

  • Armature (Coil)

  • Rotor

  • Stator

  • Carbon brushes

  • Slip Rings

DC Generators

  • An electrical machine which converts mechanical energy into direct current electricity.
  • Can also be used as a DC motor without construction changes

Parts of a DC Generator:

  • Stator
  • Armature core/Rotor
  • Armature Winding
  • Commutator
  • Carbon Brushes

Working Principle:

  • Based on Faraday's law of electromagnetic induction.
  • Dynamically induced EMF is produced in the conductor.
  • Fleming's right-hand rule determines the direction.