Describe a magnet and coil induction experiment
Specify apparatus, controlled observations and repeated comparisons for a school induction demonstration.
Cross-referenced from the related Cambridge IGCSE Chemistry 0620 or Physics 0625 teaching to the 0652 syllabus. Exact 0652 Core/Supplement objective coverage and this final-series course’s examiner fit still need specialist review. Written practice is self-checked and does not predict a Cambridge grade or demonstrate supervised laboratory competence.
Before you begin
- Distinguish induced e.m.f. from current.
- Read a signed centre-zero scale.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
What does a centre-zero detector allow you to observe?
What you will learn
- Specify apparatus, controlled observations and repeated comparisons for a school induction demonstration.
- Plan the apparatus, changing condition, stationary control and signed measurements of induction.
Use a sensitive detector and no supply in the receiver
Connect a school coil to a sensitive centre-zero galvanometer or suitable signed voltage detector. Move a bar magnet toward the coil, hold it still, then withdraw it. A deflection during movement and a zero return during the fixed hold demonstrate the changing-condition requirement. The receiving coil does not need an external electrical supply.
Keep coil orientation, magnet pole and detector connections unchanged while comparing approach and withdrawal. The two movements give opposite signs under the same connections. Swapping the approaching pole also reverses the sign. A meter sign is defined by its terminals; without that convention, positive does not name a universal direction.
Make comparisons controlled and repeatable
To compare speeds, keep the same magnet, coil, path and travel interval, move more slowly and more quickly, and compare peak deflection with repeated trials. To compare turns or magnet strength, change that one factor while holding speed, geometry and the detector circuit appropriately constant. Current measurements can also depend on circuit resistance.
The class demonstration uses suitable school apparatus, secure components and the teacher’s safety arrangements. Do not connect the receiving coil to mains. A written method checks planning and interpretation; it does not prove that the learner has performed an accurate practical or met the full practical-assessment requirements.
Sources for this lesson
Pause and explain
With magnet pole and terminals unchanged, approach and withdrawal produce what comparison?
Worked example
A coil detector gives +0.4 divisions on approach, 0 during hold and −0.4 on equal-speed withdrawal. Interpret without a supplied current calibration.
Show the worked solution
- Movement changes the linked field.
- Opposite movement reverses the sign with unchanged terminals.
- Divisions alone are not amperes or volts.
Answer Opposite signed deflections during change; no sustained hold response; calibration is needed for physical units.
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.
Write a short magnet–coil induction method including approach, hold and withdrawal.
Give me a hint
Include apparatus and expected observations, not just the conclusion.
Compare my reasoning
- Connect a suitable coil to a sensitive centre-zero detector.
- Approach, hold and withdraw the magnet with unchanged pole and terminals.
- Expect a deflection, zero steady hold and an opposite deflection.
A controlled approach–hold–withdrawal sequence demonstrates induction and sign reversal.
Look for these in your work
- Name the detector.
- Include a stationary control.
How would you compare magnet movement speeds fairly using detector peaks?
Give me a hint
Hold magnet, path, coil and measurement setup fixed.
Compare my reasoning
- Use the same pole and travel path.
- Compare slow and fast motion under unchanged circuit conditions.
- Repeat and compare peak magnitudes.
Change speed alone and compare repeated peak magnitudes.
Look for these in your work
- Control the other factors.
- Do not use a single uncontrolled reading as proof.
A report gives deflections +3 and −3 divisions but claims these are exactly ±3 A without a calibration. Correct it.
Give me a hint
A scale number needs its physical-unit relationship.
Compare my reasoning
- The signs identify opposite detector responses.
- Divisions measure indicated scale positions.
- A current calibration is required to convert them to amperes.
Report ±3 divisions and opposite signs; exact amperes are not established.
Look for these in your work
- Preserve the observed evidence.
- Identify the missing calibration.
Common mistakes
- Keep terminals and pole fixed for a comparison.
- Detector divisions are not automatically A or V.
- No mains supply is needed in the receiving coil.
What can you explain now?
Why include the stationary hold in the experiment?
Compare with the explanation
It controls for a magnet being present without changing linking.
It separates steady-field proximity from the changing condition producing induction.
After trying it yourself, choose your next review. This is your self-assessment.
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Make it stick
Plan the apparatus, changing condition, stationary control and signed measurements of induction.
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.