Uses of electromagnets How would our world look like without electromagnetism?

19/05/2016

Starter

Discuss on your table

1. How to make an electromagnet

2. Factors affecting the strength of an electromagnet

3. Uses for electromagnets

Aims

Aims:

To understand and explain how a speaker works

To understand and explain how an electric bell works

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

Fill out the worksheet

Coil Magnet Cone 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 __________. This produces a sound.

The vibrating cone produces ___________.

COIL

MAGNET

CONE

•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 __________. This

produces a sound.

•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 guideway or track, making electromagnets.

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

The train floats over the guideway 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?

Electromagnets: summary