Revision as of 06:06, 25 February 2009

Outcomes

• Pupils can predict and draw the direction of a magnetic field around a wire
• Pupils can use the right hand grip rule to draw the magnetic field around 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
• Pupils can recall how to make an electromagnet stonger
• 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 double 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.

Practical: To investigate whether placing different materials inside a solenoid will increase the magnetic field strength of the solenoid or not. Students to record observations noting the following:

• must keep the number of turns on the solenoid the same (fair test)
• each bar placed inside the solenoid must be the same size and shape (fair test)
• students can test strength of this 'electromagent' by using it to pick up paper clips or 10 grammes masses (depending on what number of turns are used.

Plenary

'Did any of the materials make the elctromagnet stronger? Which ones?'

'Did any of the materials make the elctromagnet weaker?'

'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?'

Conclusions:

• Magnetism is 'induced' in some materials like iron when they are placed in a magnetic field..
• Soft iron is called a 'soft magnetic material' because is gains and loses magneism easily. Materials that keep their magnetism for long periods are called 'hard magnetic materials'.

'What have you used in practicals recently that must be made from a hard magnetic material?'

Homework

Additional Information

Resources Required

hollow solenoids - prewound if easier variety of cores of identical size but different materials : soft iron, steel, wood, plastic, aluminium, plasticine. paperclips 100 gramme mass sets high current dc power supplies

Textbook References

Website References

Skills Addressed

Safety/Hazards

solenoid wire can get hot

Notes