Electromagnetic Induction

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Electromagnetic Induction
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Electromagnetic Induction

• Motion of a magnet in a coil or loop creates
  (induces) voltage
• If coil is connected to complete circuit, current
  flows
• Relative motion is neededit doesnt matter which
  moves, the magnet or the coil
• Amount of voltage depends on rate of motion and
  number of loops in coil

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Faradays Law

• The induced voltage is proportional to the number
  of loops times the rate of change of the magnetic
  field
• Magnetic field is changed by motion or by
  changing the strength of the field in an
  electromagnet

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Generators

• Rotating a coil in a magnetic field will create
  alternating current
• As coil rotates, amount of magnetic field
  enclosed by loop changes, inducing a changing
  voltage
• Frequency of alternating current is the same as
  frequency of rotation of the coil
• Energy is converted from some mechanical form to
  electrical

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Motors and Generators

• Both have same parts
• Motors convert electrical energy to mechanical
  movement using the magnetic force on a moving
  charge to move the coil
• Generators convert mechanical to electrical by
  using the magnetic force due to the coil movement
  to move the charges through the wire

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Transformers

• Two coils of wire wound on the same iron core so
  that changes in the magnetic field of the first
  coil (primary) induce voltage across the second
  coil (secondary)
• If ac flows through primary, ac is induced in
  secondary
• Voltage in secondary depends on ratio of turns in
  primary and secondary

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Transformers

• If secondary has more turns, than transformer is
  called step-up and voltage is increases
• If secondary has fewer turns, then is called
  step-down and voltage is decreased
• Power is not increased so if voltage is stepped
  up, current is reduced

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Transformer Equations

• Primary turns Primary voltage
• Secondary turns Secondary voltage
• (Voltage x current)p (voltage x current)s

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Power Transmission

• Almost all electrical energy is sold as ac
  because it is easy to change voltage using
  transformers
• High voltage and fairly low currents are used to
  transmit power over long distances
• This reduces losses due to heating in the wires
• Voltage is stepped down to 120 V for homes

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Electric and Magnetic Fields

• Faradays law holds even if no conductor is
  present
• A changing magnetic field induces an electrical
  field
• Maxwell extended Faradays idea to say a changing
  electrical field induces a magnetic field

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Electrical and Magnetic Fields

• Electrical and magnetic fields are perpendicular
  to each other
• Magnitude of induced field is proportional to
  rate of change of the other field
• Explained operation of electromagnetic waves
• Speed of light is only speed where induction will
  continue without energy gain or loss