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Uses of electromagnets 05/09/2016 ©cgrahamphysics.com 2016

Which one is the odd out?

05/09/2016 ©cgrahamphysics.com 2016

Starter Discuss on your table

• 1. How to make an electromagnet

• 2. Factors affecting the strength of an electromagnet

• 3. Uses for electromagnets


Aims • To understand and explain how a speaker works

• To understand and explain how an electric bell works

Key words

• Armature

• Reed switch

• Solenoid

• Core

• Loud speaker

• Relay


How would our world look like without electromagnetism?

05/09/2016

Have you ever wondered?

The bigger picture

©cgrahamphysics.com 2016

What are electromagnets

• In electromagnets the magnetism can be switched on and off by switching an electric current on and off.

• For example electromagnets attached to cranes are used to move wrecked cars around in a scrap yard.

Current on Current off


Loudspeakers From learning about electromagnets we know:

• When a current passes through a coil of wire it creates a magnetic field

• If the coil of wire is placed near a magnet what will happen?

• If the current changes direction, what will happen?

• If the current continuously changes direction, what will happen?


Loudspeakers


How does a loudspeaker work • An electrical signal is translated into an audible sound • Speakers contain an electromagnet and a permanent

magnet • Reversing the direction of the

current flips the poles of the magnet. • The direction of its magnetic field is also changed. • Electromagnet is in turn attracted to and repelled from the

permanent magnet • The electromagnet is attached to a cone made of a flexible

material which amplifies these vibrations • Sound waves are traveling towards your ears. • How A Speaker Works.flv


How A Speaker Works.flv



COIL

MAGNET

CONE

Fill out the worksheet


The signal generator sends an electrical ___________ through

the coil.

•The ________ becomes magnetised. This pulls the coil

towards the ____________.

•The coil is attached to the _________ so as the coil moves the

cone also ________.

•As the current in the coil __________ the coil moves back and

forwards, causing the cone to __________.

•The vibrating cone produces ___________.

current

coil

magnet

cone

moves

changes

vibrate

sound


Uses of electromagnets – electric bell

When the circuit is closed, the

electromagnet pulls the

armature towards it, causing

the hammer to strike the bell.

The movement of the

armature breaks the circuit,

and the hammer returns to its

original position.

This sequence repeats,

causing the bell to sound

continuously.

The circuit for a door bell includes an electromagnet.


Label the diagram – electric bell


Task

• Join Edpuzzle using the code eLpo4r

• Answer the questions while watching the video “Application of electromagnets”


Maglev trains • Maglev is short for magnetic levitation. Maglev trains can

travel at speeds of up to 310 mph (500 kph).

• Metal coils line a guide way or track, making electromagnets.

• There are large guidance magnets attached to the underside of the train.

• The train floats over the guide way on a ‘cushion’ of air which eliminates friction between the train and the track.


Using electromagnets – door bells


Plenary • Give two ways of increasing

the strength of an electromagnet.

• Explain why an iron core is better than a steel core for an electromagnet.

• Describe how an electromagnet is used to move cars around in a scrap yard.

• Why is an electromagnet, rather than a permanent magnet used to remove a steel splinter from a metal-worker’s eye?

• Why can a Maglev train go faster than other trains?

Use Coach Robin to take turns in answering these questions


Electromagnets: summary


Key words • Armature - The iron part of a relay that moves when electricity

is flowing in the solenoid (or electromagnet).

• Relay - A switch that is switched on and off by electricity.

• Reed switch - A switch made from two thin pieces of metal, which closes when it is in a magnetic field.

• Solenoid – a coil of wire

• Core - A solid bar inside an electromagnet – usually made of iron.

• Loud speaker – an electromagnet, that switches the direction of current flow, causes a cone to vibrate


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