5-MAG-2

Outcomes

• Pupils can recall ways to magnetise and demagnetise ferromagnetic materials
• Pupils can explain the difference between magnetically soft and hard materials
• Pupils know how to make an electromagnet and how to make it stronger

Specification References

6.3 describe the properties of magnetically hard and soft materials

6.5 understand that magnetism is induced in some materials when they are placed in a magnetic field

6.8 recall that an electric current in a conductor produces a magnetic field round it.

6.9 describe the construction of electromagnets

Starter

Pupils use the mini white boards to answer questions from previous lesson 'what is a magnetic field?', 'where is the magnetic field uniform?' & 'draw the magnetic field pattern around a bar magnet'.

Main Body of Lesson

Practical: To investigate how the current in a wire wound electromagnet or the number of turns affects the strength of the electromagnet. Pupils will have done this in the 2nd form so this shouldn't take long. To see a noticeable effect they should do large changes to the number of coils on the steel bar. Depending on the length of the wire this could be 20 turns at a time. They should also vary the current (with a fixed number of turns) to see the effect this has. Finally they can use a wooden core if they want. It's pretty rubbish if they do.

Plenary

Look at the difference between an iron nail and a steel nail and introduce the idea of magnetically soft and hard materials. Can also demo a magnetising and demagnetising coil with dc and ac.

Recap the main points of magnetism that have been covered.

Homework

• Read Complete Physics pages 206 - 209 and answer questions at the bottom of 207 & 209.
• Investigate the design of magnets in particle accelerators - how do they differ to the bar magnets and electromagnets that you have met?

Additional Information

Resources Required

• Make an electromagnet kit (steel bar, wire, croc clips, high current ammeter, variable resistor)
• Iron and Steel "nail" (bars are fine)
• Magnetising/Demagnetising coil, AC/DC supply

Textbook References

Complete Physics pages 206 - 207

Safety/Hazards

• When using iron filings wear safety goggles.
• Solenoid wire can get hot, this is due to large currents caused by High voltages