Electromagnetic Induction

From ZuluNotes - Free Leaving Cert Notes

The section on electromagnetic induction deals with the conversion of magnetic energy to electrical energy, and visa verse. You may have already studied that an electric current causes a magnetic field around it.

Contents 1 Electromotive Force 2 Types of Induction 2.1 Mutual Induction 2.2 Self Induction 3 Inductors 4 Transformers

Electromotive Force

• Electromagnetic induction occurs when a changing magnetic field causes an emf to be induced in a coil.
  • This is referred to as an induced emf.
• The induced emf is proportional to the rate of change of flux (Faraday's Law).
• The direction of the induced emf will always try to oppose the force causing the emf (Lenz's Law).
  • Otherwise the Principle of Conservation of Energy would be violated.
• The electric generator is based on the principle of electromagnetic induction (dynamo, alternator).

Types of Induction

Mutual Induction

• The a.c. going through a coil causes an alternating magnetic field around it.
• This alternating magnetic field will induce an emf in a nearby coil.
• A current will appear in this second circuit.

Self Induction

• The a.c. going through a coil causes an alternating magnetic field around it.
• This alternating magnetic field will induce an emf in the coil.
• The emf induced will oppose the flow of current producing it (According to Lenz's law).
• This back emf will reduce the overall current.

Inductors

• A coil opposes d.c. with it's ohmic resistance.
• A coil opposes a.c. with it's ohmic resistance and back emf.
• A greater frequency of a.c. will cause a larger back emf.
• Inductors serve many uses, including:
  • devices to tune radios.
  • to deliver a smooth d.c. current.
  • dimmer switches.

Transformers

• Transformers change the values of current and voltage, while (theoretically) keeping the same power.
• They work on the principle of induction.
  • V_i causes a.c. in primary coil.
  • This causes an alternating magnetic flux in the iron core.
  • The flux induces an emf in the second coil (V_o).
  • The size of V_o depends on N_s.