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Motors Book pg 187 – 189

Syllabus 6.11 – 6.14

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The Motor effect – where?

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What device does not use a motor?


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



Have you ever wondered

How would a world without motors look like?

The bigger picture

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

Fleming’s left hand rule


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

Right Hand rule # 3


10 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.

reversing the current reversing the magnetic field

Changing the direction of the force


Increasing the size of the force


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?



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.

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


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



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

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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