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Motors Book pg 187 – 189
Syllabus 6.11 – 6.14
©cgrahamphysics.com 2015 The Butterfly Effect 05/09/2016
The Motor effect – where?
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What device does not use a motor?
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Aim • Know the link between movement, magnetism and
current
• Know how electric motors work
• Use Fleming’s left hand rule or the 3rd right hand rule
Key words
• Motor effect - motor
• Electromagnetism - commutator
• Fleming’s rule or RHR #3 - brushes
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Have you ever wondered
How would a world without motors look like?
The bigger picture
What is a motor?
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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.
Which devices in your home
use an electric motor?
The Motor Effect
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If a wire carrying a current is placed into a magnetic field, an interesting thing happens. As part of the GCSE course, you are required to know which way a wire placed into a magnetic field moves
Fleming’s left hand rule
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F = force on wire B = external magnetic field I = current
Right Hand rule # 3
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The motor effect
When current flows through a wire held in a magnetic field,
it can create a force that moves the wire.
This is called the motor effect.
If the magnetic field and current
are at right angles to each other,
this results in the maximum force
possible on the wire.
If the magnetic field and current
are parallel to each other, there
is no force.
force
What do you think happens if the wire is held at a different
angle to the magnetic field?
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Wire in a magnetic field
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The direction of the force acting on a wire in an
electromagnetic field can be reversed by:
The direction of the force is therefore relative to both the
direction of the magnetic field and the current.
reversing the current reversing the magnetic field
Changing the direction of the force
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Increasing the size of the force
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The motor effect: true or false?
How can we turn a wire into a motor? • One wire won’t make a
motor • How about a complete
loop?
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Coil in a magnetic field
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DC electric motor simulation
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Producing continuous rotation
Unless the direction of the current is reversed every
half turn, the coil will stop rotating. This happens when
the current-carrying coil and the lines of force from the
permanent magnets are parallel.
A device called a
commutator is used to
momentarily break the
circuit and change the
direction of the current.
This ensures that the
coil turns continuously.
Parts of a motor
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coil
brushes
battery
axle
Split-ring commutator
magnet
This reverses the current in the coil to keep it rotating.
These provide a permanent magnetic field.
These provide the connection to the battery.
When current passes through this, forces act on it.
This allows the coil to spin. This provides the energy source.
To increase the rate at which the motor turns
• Increase the number of loops
• Increase the strength of the magnetic field
• Increase the current flowing through the wire
• A real motor differs from a loop of wire
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Practical Motors
• The permanent magnets are replaced with curved electromagnets capable of producing very strong magnetic fields
• The single loop is replaced with several coils of wire wrapped on the same axis
• This makes the motor more powerful and allows it to run more smoothly
• The coils are wrapped on a laminated soft iron core. This makes the motor more efficient and more powerful
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Energy transfers in motors
A motor converts electrical energy into useful
mechanical energy.
Motors are not 100 percent efficient. Some energy is lost as
heat energy.
friction
electrical
mechanical
resistance
other losses
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Plenary: Multiple-choice quiz
Key words • Motor effect - the term used when a current-carrying wire in the
presence of a magnetic field experiences a force. • Motor – a loop of wires spinning around an axle driven by a
battery • Commutator – reverses the current and keeps the coil spinning • Brushes – provide the connection to the battery • Electromagnetism - the interaction of electric currents or fields
and magnetic fields. • Fleming’s left hand rule – FBI - F = force on wire, B = external
magnetic field, I = current. F = thumb, B is index fg, I = middle fg • RHR #3 – thumb points in direction of current, flat finger in
direction of external field from N to S, force comes out of palm of your hand
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