Download 10. Motors and Generators

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Transcript
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Electromagnetism and movement
What is the link between movement, magnetism and electric
current?
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Wire in a magnetic field
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Changing the direction of the force
The direction of the force acting on a wire in an
electromagnetic field can be reversed by:
 reversing the current
 reversing the magnetic field
The direction of the force is therefore relative to both the
direction of the magnetic field and the current.
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Fleming’s left-hand rule
It is possible to predict the direction of the force acting on
a wire – its motion – if the direction of the current or the
magnetic field are known. Fleming’s left-hand rule is
used to do this.
thuMb = Motion
First finger = magnetic Field
seCond finger = Current
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Increasing the size of the force
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Coil in a magnetic field
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The motor effect: true or false?
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What are electric motors?
How many items do you own that contain an electric motor?
An electric motor is a device that
converts electrical energy into
mechanical energy to produce a
turning effect.
Most motors are powered using direct
current (DC), which is produced by
cells and batteries.
Motors powered by mains electricity
use alternating current (AC).
These motors use electromagnets
rather than permanent magnets.
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How does an electric motor work?
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DC electric motor simulation
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How do we increase motor strength?
Would the same strength motor be used in both of these?
How can the strength of an electric motor be increased?
 increase the current flowing through the coil
 increase the strength of the magnet
 increase the number of turns on the coil
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Inducing current in a wire
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Fleming’s right-hand rule
It is possible to predict the direction of the induced current
produced by a generator if the direction of the force (or
motion) or the magnetic field are known. Fleming’s righthand rule is used to do this.
thuMb = Motion
First finger = magnetic Field
seCond finger = Current
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What is electromagnetic induction?
When current flows through a wire held in a magnetic field,
a force is created that moves the wire.
The opposite is also possible: if a
wire is moved across a magnetic
field, a current is produced. This is
called electromagnetic induction.
Induction also occurs if a magnet is
moved in a coil of wire, or if a coil of
wire rotates in a magnetic field.
In all these methods of inducing a current, the wire and
magnetic field move perpendicular to each other. If they
move parallel to each other, no current is induced.
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Inducing current in a coil
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What are generators?
A generator is a device that converts mechanical energy
into electrical energy. It is the opposite of an electric motor.
Power stations use generators
to produce electricity on a large
scale. Mechanical energy is
provided by rotating turbines
that can be powered by:
 high-pressure steam – in
coal, oil, gas and nuclear
power stations
 wind – in wind turbines
 falling water – in hydroelectric power stations
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How do AC generators work?
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AC generator simulation
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Increasing the size of the induced current
How can the size of an induced current be increased?
 increase the speed at which the coil rotates
 increase the strength of the magnetic field
 increase the number of turns in the coil
 increase the total area of the coil.
In a power station
generator, an
electromagnet is often
used as this can provide
a stronger magnetic field
than is possible with a
permanent magnet.
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Factors affecting induced current
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Induction: true or false?
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Glossary
 alternating current – A current that constantly changes




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direction. It is produced by most electrical generators.
commutator – The part of a motor that enables the coil to
rotate using direct current.
direct current – A current that always flows in the same
direction. It is produced by cells and batteries.
generator – A device that converts mechanical energy into
electrical energy.
induction – Generating a current in a wire by moving the
wire in a magnetic field, or by moving a magnet inside a coil.
motor – A device that converts electrical energy into
mechanical energy.
slip rings – The parts of a generator that enable the
rotating coil to produce alternating current.
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Anagrams
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Multiple-choice quiz
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