Induce voltage by changing the field linking a coil
Explain induction with a stationary conductor and a changing linked field, including a stationary-field control.
Exam scope and assessment notes
Core and Extended · Physics 0972, 2026–2028. Use the stated source, operating conditions and meter ranges. Written practice is self-checked. Human subject-teacher review, supervised practical competence and cumulative assessment remain pending. Cambridge states that IGCSE 0972 has the same subject content as IGCSE 0625, with 9–1 grading. This StudyForA pathway maps the 2026–2028 syllabus only. This 9–1 graded qualification is available only in a limited number of administrative zones. Confirm that your centre can enter you for this code and exam series with Cambridge International. Cambridge has published a separate syllabus for 2029. StudyForA has not reconciled that version yet; this page supports exams in 2026, 2027 and 2028 only.
Before you begin
- Describe a magnetic field around a magnet or coil.
- Distinguish a steady state from a changing state.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
What does a stationary bar magnet provide around it?
What you will learn
- Explain induction with a stationary conductor and a changing linked field, including a stationary-field control.
- Describe the actual change in linked magnetic field, including controls where everything stays fixed.
The conductor need not move
A changing magnetic field linking a conductor can induce an e.m.f. even if the conductor itself is stationary. Moving a bar magnet toward or away from a fixed coil changes the linked field. A nearby electromagnet with changing current can provide a field change without moving either coil.
A magnet held still in a fixed position beside a stationary coil gives an approximately steady linked field, so no sustained induced e.m.f. occurs in that unchanged arrangement. Field strength being large is not by itself sufficient: the linking must change.
Name the change, not just the object
Compare three states: magnet approaching, magnet held still, and magnet withdrawing. Approaching and withdrawing can induce e.m.f.; holding still after the movement stops gives zero in the ideal steady-field case. Changes in coil orientation or effective linked area can also alter linking even when a field source is fixed.
An induced e.m.f. drives current only through an appropriate complete path. This is induction between circuits or between a moving magnet and coil; it is not charge directly travelling from the magnet into the coil. Supplement work later explains the induced direction.
Pause and explain
A strong magnet and coil are held fixed. What is expected after transients have ended?
Worked example
A magnet approaches a fixed coil, is held stationary, then is withdrawn. Identify the induction states.
Show the worked solution
- Approach changes the linked field.
- Holding both fixed leaves it steady.
- Withdrawal changes it again.
Answer Induction during approach and withdrawal; none sustained during the fixed hold.
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.
Classify a fixed coil with magnet approaching, held still and withdrawing.
Give me a hint
Identify linked-field change in each stage.
Compare my reasoning
- Approach changes linking.
- A fixed hold keeps it steady.
- Withdrawal changes linking again.
Approach: induction; fixed hold: none sustained; withdrawal: induction.
Look for these in your work
- Include all stages.
- State the steady arrangement assumption.
A nearby source electromagnet and receiving coil are both fixed. Explain why increasing source current can induce e.m.f. in the receiving coil.
Give me a hint
Changing current changes the source magnetic field.
Compare my reasoning
- Source current increases.
- Its linked magnetic field changes.
- The receiving coil can develop induced e.m.f.
Changing source current can induce e.m.f. without mechanical movement.
Look for these in your work
- Name the field change.
- Do not transfer charge between separate circuits.
A student says induction always requires the receiving wire to move. Use two counterexamples.
Give me a hint
Change the linked field while keeping the receiver fixed.
Compare my reasoning
- Move a magnet toward a fixed coil.
- Change current in a nearby fixed electromagnet.
- Both change the field linking the stationary receiver.
A moving magnet or changing source current can induce in a stationary receiving coil.
Look for these in your work
- Provide two distinct changes.
- Keep the receiving conductor stationary.
Common mistakes
- A strong steady linked field is not enough.
- Changing source current can induce without motion.
- Charge does not transfer from magnet to coil.
What can you explain now?
Can a stationary coil have induced e.m.f.?
Compare with the explanation
Yes, if its linked magnetic field changes
Induction can follow a changing linked field even though the conductor remains still.
After trying it yourself, choose your next review. This is your self-assessment.
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Make it stick
Describe the actual change in linked magnetic field, including controls where everything stays fixed.
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.