MOTORS - WordPress.com · 2015. 10. 18. · PARTS OF A MOTOR coil brushes battery axle Split-ring commutator magnet This reverses the current in the coil to keep it rotating. These

Book pg 187 – 189 Syllabus 6.11 – 6.14

MOTORS

How does that work?

© WWW.CGRAHAMPHYSICS.COM 2015

ELECTROMAGNETISM AND MOVEMENT

What is the link between movement, magnetism and current?


KEYWORDS: Fleming’s le4 hand rule, 3rd right hand rule

Understand how electromagnets can be used to make things

move

ALL – State how electromagnets can be used in motors MOST – Use Fleming’s le8 hand rule or the 3rd right hand rule

© www.cgrahamphysics.com 2015

WHAT IS A 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.

Which devices in your home use an electric motor?


THE MOTOR EFFECT

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

LO: Understand how electromagnets can be used to make things move


FLEMING’S LEFT HAND RULE

LO: Understand how electromagnets can be used to make things move

F = force on wire B = external magnetic field I = current


RIGHT HAND RULE # 3


8 of 26 © Boardworks Ltd 2012

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?


Wire in a magnetic field


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.

l  reversing the current l  reversing the magnetic field

Changing the direction of the force


Increasing the size of the force


The motor effect: true or false?

•  One wire won’t make a motor •  How about a complete loop?

HOW CAN WE TURN A WIRE INTO A MOTOR?



Coil in a magnetic field


DC electric motor simulation


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

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. © WWW.CGRAHAMPHYSICS.COM 2015

•  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

TO INCREASE THE RATE AT WHICH THE MOTOR TURNS


•  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

PRACTICAL MOTORS



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


Plenary: Multiple-choice quiz

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MOTORS - WordPress.com · 2015. 10. 18. · PARTS OF A MOTOR coil brushes battery axle Split-ring commutator magnet This reverses the current in the coil to keep it rotating. These