3-MAG-02

Outcomes

• Pupils can use the right hand grip rule to draw the magnetic field around a wire, a flat circular coil and a solenoid
• 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
• Pupils can explain that the magnetic field of an electromagnet is the result of the magnetic field around the current (in the wires) and the alignment of domains in an iron core

Specification References

6.3 recall 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 magentic field round it.

6.9 describe the construction of electromagnets

6.10 sketch and recognise magentic field patterns for a straight wire, a flat circular coil and a solenoid when each carrying a current

Starter

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

Main Body of Lesson

For a single lesson:

Demo on OHP using iron filings or plotting compasses the shape of the magneic field around:

• a straight wire
• a flat coil
• a solenoid

Students to sketch shapes of magnetic fields for each. Introduce the right hand grip rule and how it is used to predict the direction of the magnetic field.

Then for two singles or a double lesson:

Practical: To investigate how the current in a wire wound electromagnet or the number of turns affects the strength of the electromagnet. Use this worksheet to help the pupils plan their fair test and record the data. The key points in this experiment are:

• Making this experiment a fair test. The pupils should select the variable they wish to investigate. They need to write about how they will make it a fair test.
• They need to measure the average mass of the paper clips and find an average weight. This improves the speed of the experiment and the accuracy of results; discuss with the pupils the idea of taking a larger sample to make the value of the weight of a paper clip more reliable.
• The paper clips are hung end to end.
• The pupils will have to share their results at the end.
• Using the large blue power supplies, set the voltage to 6V.
• If pupils vary the number of turns from 5 to 35, then a voltage of 4 amps should be used.
• If pupils vary the current, then they should have 20 turns of wire and vary the current from 1.5 amps to 4 amps.

Plenary

Ask open ended questions to test their understanding:

'What do you think is happening to a material, like soft iron, which makes the electomagnet stronger?

'What happens to the electromagnet with the soft iron bar inside when the current is switched off? Why?'

'What do you think would happen if you increased the current in the wire to 10A?'

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

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