Explain useful permanent-magnet applications
Connect retained magnetisation to compasses, magnetic catches and the fixed field in a loudspeaker.
Mapped to the named 0654 section using teaching from the corresponding single-science course. A 0654-specific review of every Core and Supplement objective is still in progress. Written practice is self-checked; it does not demonstrate supervised laboratory competence or award an official Cambridge grade.
Before you begin
- Compare permanent and temporary magnets.
- Explain attraction and compass alignment.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
Which property distinguishes the stated permanent-magnet role?
What you will learn
- Describe typical permanent-magnet uses.
- Link a use to retained magnetisation without a continuously powered magnetising coil.
Use a field that remains available
A compass uses a permanently magnetised needle that turns in the surrounding magnetic field. A magnetic cupboard catch uses retained attraction to hold the door closed against a suitable magnetic piece. Neither use requires a continuous current merely to maintain the permanent magnet's magnetisation.
A permanent magnet can supply the fixed magnetic field in a moving-coil loudspeaker. The changing electrical signal drives the coil within that field, and the cone vibrates. The permanent magnet is one component; it does not alone encode the music or create the changing current.
Choose the property rather than memorising a device list
Useful retention makes a permanent magnet suitable when an ongoing field or attraction is desired. A catch can still be opened by a sufficient applied force. Permanently magnetised does not mean permanently attached to every object or impossible to separate.
Some devices use both permanent magnets and powered coils. Identify which component supplies the retained field and which is controlled by current. A loudspeaker example here introduces the use; the later motor-effect sequence teaches its force mechanism in more detail.
Sources for this lesson
Pause and explain
What does a permanent magnet supply in the described loudspeaker?
Worked example
Explain why a magnetic cupboard catch can hold a door without a powered coil.
Show the worked solution
- The catch contains a permanent magnet.
- Its magnetisation is retained.
- It attracts a suitable magnetic piece on the door.
Answer Retained magnetisation provides the attractive holding force without a continuously powered coil.
Try a topic test
Choose Easy, Normal or Difficult. Save your answers and open worked review after finishing.
Test this topic →From guided practice to a new situation
Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
Explain a compass as a permanent-magnet use.
Give me a hint
Identify the magnetic component and its response.
Compare my reasoning
- The needle retains magnetisation.
- It turns in the surrounding field.
- Its north tip indicates local field direction.
A permanently magnetised needle aligns with the local field.
Look for these in your work
- Identify the needle.
- Link retention and alignment.
Explain the permanent-magnet role in a cupboard catch.
Give me a hint
Connect retained magnetisation to the suitable piece it attracts.
Compare my reasoning
- The catch contains a permanent magnet.
- It retains its poles without a powered coil.
- Attraction helps hold a magnetic door piece.
Retained attraction holds a suitable magnetic piece on the door.
Look for these in your work
- Name the magnet's property.
- Specify a magnetic partner.
A loudspeaker has a permanent magnet and a signal-driven coil. Does the magnet alone contain the changing sound information?
Give me a hint
Separate the retained field from the changing electrical input.
Compare my reasoning
- The magnet supplies the fixed field.
- The input signal changes the coil current.
- The changing information is not stored in the permanent magnet alone.
No; the magnet supplies the field and the driven coil receives the changing signal.
Look for these in your work
- Identify both roles.
- Avoid calling the entire device unpowered.
Common mistakes
- A permanent magnet does not mean inseparable contact.
- Distinguish the magnet from a powered coil in the same device.
- Explain the useful property.
What can you explain now?
Does a permanent magnet require a continuous current to retain its useful magnetisation?
Compare with the explanation
No.
Retained magnetisation is the property used in these examples.
After trying it yourself, choose your next review. This is your self-assessment.
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Make it stick
Explain permanent-magnet uses through retained field or attraction and separate other device components.
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.