5-MAG-3

Outcomes

• students can sketch magnetic field patterns for various electromagnets and make link to bar magnets
• students explain how the electric bell and different relays work
• pupils see how magnets and electromagnets work together to produce movement in a speaker

Specification References

• 6.9 describe construction of electromagnets
• 6.10 sketch and recognise magnetic field patterns for a straight wire, a flat circular coil and a solenoid when each is carrying a current

Starter

• Using the mini white boards ask pupils to recall the shape of a magnetic field around a bar magnet. Identify the important aspects: continuous filed lines and arrows for direction. Can also ask for ways to strengthen an electromagnet (from last lesson)

Main Body of Lesson

Demo the 3 shapes of electromagnet (single wire, flat coil and solenoid). Use plotting compasses and/or iron filings to show field lines. Wires get pretty hot due to high currents. Pupils need good replicas of these in their notes as they need to be able to sketch and recognise them.

The main practical is to build a small speaker. We'll deal with the motor effect more formally in the next lesson but start by having pupils think about what happens when two magnets are brought together. Does it matter if one of these is an electromagnet? Speakers can be tested with pupil music which they really enjoy.

Although they don't now need to know about relays and electric bells they make a suitable extension if the practical has worked well.

Plenary

• Use the 'Electric Bell' and 'Relays' worksheet. Pupils should stick them in their books and use them to fully explain how they work.

Homework

• Complete Physics texbook - page 209, Q 1-4

Additional Information

Resources Required

• single wire, flat loop and solenoid demos, plotting compasses and iron filings
• build a speaker kits
• electric bell demo, different relay demos, circuit breakers RCD's, coils, power supplies

Textbook References

• None

Website References

• None

Safety/Hazards

• With high currents the wires may get hot.

Notes

• None