uses of electromagnets - … 19, 2016 · fill out the worksheet coil magnet cone the signal...
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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?
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 ___________.
•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.
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.
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?
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