Transcript Electromagnetic Induction Notes

Electromagnetic Induction
Notes
CP Physics
Ms. Morrison
• 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?
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
Electromagnetic Induction, pg 2
• 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
Electromagnetic Induction, pg 3
• 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
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.
Generators
• 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
Generators, pg 2
• 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:
– 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)
Generators, pg 4
• 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
• 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
• 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)
Transformers, pg 2
• 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
Power Transmission
• 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
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