Electromagnetism

1. 16-18/21 Electromagnetism How can we make an electromagnet? Starter: Make a list of uses for magnets. Too easy? What are magnets made of ?

2. 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.

3. 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?

4. 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.

5. 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.

7. 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.

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

9. 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.

10. 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

11. 18/21 Electromagnetic induction How can a current be induced in a coil? Starter What can you remember about how electricity is made?

13. 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.

14. 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

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

16. 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?!

17. 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.

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

22. Work your way through the questions.