Electromagnetic Induction Notes CP Physics Ms. Morrison

1820 – Oersted discovered that electric current produced a magnetic field 1820 – Oersted discovered that electric current produced a magnetic field Question arose if the reverse was true – Could a magnetic field be used to produce electric current? Question arose if the reverse was true – Could a magnetic field be used to produce electric current?

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

Electromagnetic Induction, pg 2 Amount of voltage produced depends on how quickly the wire moves through the magnetic field Amount of voltage produced depends on how quickly the wire moves through the magnetic field Greater number of loops in wire that move in a magnetic field = greater induced voltage, greater current in wire Greater number of loops in wire that move in a magnetic field = greater induced voltage, greater current in wire

Electromagnetic Induction, pg 3 Coil with more loops is a stronger electromagnet so it takes more force to move the magnet through the coil Coil with more loops is a stronger electromagnet so it takes more force to move the magnet through the coil Does not matter which moves – the coil of wire or the magnet – it is the relative motion of the two which induces voltage – called electromagnetic induction Does not matter which moves – the coil of wire or the magnet – it is the relative motion of the two which induces voltage – called electromagnetic induction

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

Generators Moving magnet in and out of coil to produce current Moving magnet in and out of coil to produce current –Magnet enters: induces voltage in one direction –Magnet leaves: induces voltage in opposite direction Easier to move coil inside magnet rather than move magnet back and forth in coil Easier to move coil inside magnet rather than move magnet back and forth in coil

Generators, pg 2 Generator = rotating a coil in a stationary magnetic field Generator = rotating a coil in a stationary magnetic field –Opposite of a motor –Converts mechanical energy into electrical energy

Generators, pg 3 Voltage produced by generators depend on three factors: Voltage produced by generators depend on three factors: –Number of loops in the coil (more loops = greater voltage) –The strength of the magnet (stronger = greater voltage) –The speed of rotation of the coil (faster = greater voltage) Produces alternating current (in US – 60 Hertz) Produces alternating current (in US – 60 Hertz)

Generators, pg 4 Generators used in power plants to generate electricity Generators used in power plants to generate electricity Much more complex with huge coils of wire wrapped around an iron core in a very powerful magnetic field Much more complex with huge coils of wire wrapped around an iron core in a very powerful magnetic field Turns because of the turning of a turbine (steam, water, wind) Turns because of the turning of a turbine (steam, water, wind)

Transformers Iron core around which a primary coil is wrapped and a secondary coil is wrapped Iron core around which a primary coil is wrapped and a secondary coil is wrapped Step up transformer – secondary has more loops than primary so voltage increased in secondary (increases voltage) Step up transformer – secondary has more loops than primary so voltage increased in secondary (increases voltage) Step down transformer – secondary has less loops than primary so voltage decreased in secondary (decreases voltage) Step down transformer – secondary has less loops than primary so voltage decreased in secondary (decreases voltage)

Transformers, pg 2 Principal reason most electric power is AC rather than DC – due to ease with which voltages can be increased or decreased Principal reason most electric power is AC rather than DC – due to ease with which voltages can be increased or decreased Reduces the amount of energy lost through the electrical lines transmitting the current Reduces the amount of energy lost through the electrical lines transmitting the current

Power Transmission Almost all electrical energy sold as AC because it can easily be transformed from one voltage to another Almost all electrical energy sold as AC because it can easily be transformed from one voltage to another Travels great distances at high voltages and low currents Travels great distances at high voltages and low currents Voltage is stepped up as it travels from the power plant and then stepped down as it approaches businesses and homes – until it reaches 120 volts Voltage is stepped up as it travels from the power plant and then stepped down as it approaches businesses and homes – until it reaches 120 volts