Electromagnetic Induction Electromagnetic Induction NotesNotes

CP PhysicsCP Physics

Ms. MorrisonMs. Morrison

• 1820 – Oersted discovered that 1820 – Oersted discovered that electric current produced a magnetic electric current produced a magnetic fieldfield

• Question arose if the reverse was Question arose if the reverse was true – Could a magnetic field be used true – Could a magnetic field be used to produce electric current?to produce electric current?

Electromagnetic InductionElectromagnetic Induction

• 1831 – Michael Faraday (England) 1831 – Michael Faraday (England) and Joseph Henry (US) independently and Joseph Henry (US) independently discovered that electric current could discovered that electric current could be produced by moving a magnet in be produced by moving a magnet in and out of a coil wireand out of a coil wire

Electromagnetic Induction, Electromagnetic Induction, pg 2pg 2

• Amount of voltage produced depends Amount of voltage produced depends on how quickly the wire moves on how quickly the wire moves through the magnetic fieldthrough the magnetic field

• Greater number of loops in wire that Greater number of loops in wire that move in a magnetic field = greater move in a magnetic field = greater induced voltage, greater current in induced voltage, greater current in wirewire

Electromagnetic Induction, Electromagnetic Induction, pg 3pg 3

• Coil with more loops is a stronger Coil with more loops is a stronger electromagnet so it takes more force electromagnet so it takes more force to move the magnet through the coilto move the magnet through the coil

• Does not matter which moves – the Does not matter which moves – the coil of wire or the magnet – it is the coil of wire or the magnet – it is the relative motion of the two which relative motion of the two which induces voltage – called induces voltage – called electromagnetic inductionelectromagnetic induction

Faraday’s LawFaraday’s Law

• The induced voltage in a coil is The induced voltage in a coil is proportional to the product of the proportional to the product of the number of loops and the rate at number of loops and the rate at which the magnetic field changes which the magnetic field changes within those loops.within those loops.

GeneratorsGenerators

• Moving magnet in and out of coil to Moving magnet in and out of coil to produce currentproduce current– Magnet enters: induces voltage in one Magnet enters: induces voltage in one

directiondirection– Magnet leaves: induces voltage in opposite Magnet leaves: induces voltage in opposite

directiondirection

• Easier to move coil inside magnet Easier to move coil inside magnet rather than move magnet back and rather than move magnet back and forth in coilforth in coil

Generators, pg 2Generators, pg 2

• Generator = Generator = rotating a coil rotating a coil in a stationary in a stationary magnetic fieldmagnetic field– Opposite of a Opposite of a

motormotor– Converts Converts

mechanical mechanical energy into energy into electrical electrical energyenergy

Generators, pg 3Generators, pg 3• Voltage produced by generators Voltage produced by generators

depend on three factors:depend on three factors:– Number of loops in the coil (more loops Number of loops in the coil (more loops

= greater voltage)= greater voltage)– The strength of the magnet (stronger = The strength of the magnet (stronger =

greater voltage)greater voltage)– The speed of rotation of the coil (faster The speed of rotation of the coil (faster

= greater voltage)= greater voltage)

• Produces alternating current (in US – Produces alternating current (in US – 60 Hertz)60 Hertz)

Generators, pg 4Generators, pg 4

• Generators used in power plants to Generators used in power plants to generate electricitygenerate electricity

• Much more complex with huge coils Much more complex with huge coils of wire wrapped around an iron core of wire wrapped around an iron core in a very powerful magnetic fieldin a very powerful magnetic field

• Turns because of the turning of a Turns because of the turning of a turbine (steam, water, wind)turbine (steam, water, wind)

TransformersTransformers• Iron core around which a primary coil is Iron core around which a primary coil is

wrapped and a secondary coil is wrappedwrapped and a secondary coil is wrapped

• Step up transformer – secondary has Step up transformer – secondary has more loops than primary so voltage more loops than primary so voltage increased in secondary (increases increased in secondary (increases voltage)voltage)

• Step down transformer – secondary has Step down transformer – secondary has less loops than primary so voltage less loops than primary so voltage decreased in secondary (decreases decreased in secondary (decreases voltage)voltage)

Transformers, pg 2Transformers, pg 2

• Principal reason most electric power Principal reason most electric power is AC rather than DC – due to ease is AC rather than DC – due to ease with which voltages can be increased with which voltages can be increased or decreasedor decreased

• Reduces the amount of energy lost Reduces the amount of energy lost through the electrical lines through the electrical lines transmitting the currenttransmitting the current

Power TransmissionPower Transmission

• Almost all electrical energy sold as AC Almost all electrical energy sold as AC because it can easily be transformed from because it can easily be transformed from one voltage to anotherone voltage to another

• Travels great distances at high voltages Travels great distances at high voltages and low currentsand low currents

• Voltage is stepped up as it travels from the Voltage is stepped up as it travels from the power plant and then stepped down as it power plant and then stepped down as it approaches businesses and homes – until approaches businesses and homes – until it reaches 120 voltsit reaches 120 volts