Electromagnetism How can we make an electromagnet? Starter: Make a list of uses for magnets. Too easy? What are magnets made of ? 16-18/21

Glossary Words Electromagnet – A magnet formed when a coil of wire with a current through it, its wrapped around an iron core. Electromagnetic induction – the process of inducing a potential difference in a wire by moving the wire so it cuts across magnetic field.

What do magnetic fields look like? Demo – magnet and compass. Demo - magnet and iron filings Demo making an electromagnet with a wire, nail and paper clips. How can we increase the strength of the magnet?

Notes - printed An electromagnet is made by coiling an insulated wire about an iron core. This produces a magnetic field around the bar making it temporarily magnetic. Switch off the current, and the iron will lose the magnetism. Steel is no good because it keeps its magnetism.

Uses. Read page 243 and answer these questions. 1) name 4 uses of electromagnets. 2) What is the benefit of using electromagnets in a scrap yard crane, rather than a permanent magnet. 3) Briefly describe how a circuit breaker works.

A relay switch A relay is a switch. Pass a current through the EM the armature is pulled towards it. This closes a gap and allows something to be turned on.

Increasing the strength of an electromagnet 1) increase number of coils. 2) increase current.

Mark the long answer question What is the mark out of 6? Now … correct it to make it a full mark answer using the marking criteria.

3. Quality of written communication: One mark for correct sequencing. 1 bolt out → plunger up → switch off / circuit broken any five from 5 high current flows electromagnet is stronger the iron bolt is pulled out the plastic plunger moves up the switch is lifted / open / off accept circuit is broken no current flowing to re-set the plunger must be pushed down

Electromagnetic induction How can a current be induced in a coil? Starter What can you remember about how electricity is made? 18/21

Glossary Generator – a system consisting of an iron core and coil of wire which will produce a voltage when moved. TOP TIP- on an exam question if there is a power supply it is NOT electromagnetic induction.

Generators (notes) A voltage is induced across the ends of the wire when it cuts across a magnetic field. (The conductor has to cross the magnetic field). This is electromagnetic induction. If the wire is in a complete circuit it will make an electric current

DEMOs Coil and magnet Coils on a cardboard tube and iron core page 247

The Motor Effect Electric motors work because a force produced in a magnetic field can make things move. E.g. in an electric motor. This is the motor effect. How can I work out the direction of the force?!

Which direction is the force? Your first finger points in the direction of the magnetic field (North to South). Your second finger points in the direction of conventional current (positive to negative). Your thumb points in the direction of the thrust or force on the conductor. Use a pen to write these on your hand, and work out the direction of the force.

Force Factors Increase the size of the force in the motor by – Increase size of current – Use a stronger magnet.

Work your way through the questions.