Use opposition to change for magnet and coil directions
Predict the induced magnetic pole facing an approaching or withdrawing magnet in a closed receiver.
Extended only (Supplement); Physics 0625, 2026–2028. Use the stated source, operating conditions and meter ranges. Written practice is self-checked.
Before you begin
- Use attraction and repulsion of magnetic poles.
- Relate clockwise/anticlockwise conventional coil current to its viewed pole.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
Which poles attract?
What you will learn
- Predict the induced magnetic pole facing an approaching or withdrawing magnet in a closed receiver.
- Predict opposition to the actual change, then translate near-face pole to current using an explicit viewing direction.
Oppose the change causing induction
The induced e.m.f. has a direction that opposes the change producing it. In a closed conducting coil, its induced current creates a magnetic field with that opposing effect. For a north pole approaching the coil face, the coil face becomes north and repels the approach. For the same north pole withdrawing, the face becomes south and attracts it, opposing separation.
The opposition concerns the change, not simply the source field being present. With a south pole approaching, the near coil face becomes south; with it withdrawing, the face becomes north. A stationary magnet and coil with no other field change have no sustained induced response to assign.
State the viewing face before naming current
Viewed from the magnet side looking at the near coil face, anticlockwise conventional current makes that face north and clockwise current makes it south. Thus an approaching north pole gives anticlockwise current under this view, while a withdrawing north pole gives clockwise current. Looking from the other side reverses apparent clockwise sense.
These current statements assume a closed receiver. An open coil can have induced e.m.f. but does not have the same sustained loop current or corresponding current-produced opposing field. Do not use an undefined detector positive sign as a universal clockwise convention.
Pause and explain
A south pole approaches a closed coil. What is the near face and current viewed from the magnet side?
Worked example
A north pole approaches a closed coil. Viewed from the magnet side, identify coil face and current sense.
Show the worked solution
- Oppose approach by repelling the north pole.
- The near coil face must be north.
- A north face corresponds to anticlockwise conventional current from this view.
Answer Near face north; anticlockwise from the magnet side.
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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.
A north pole approaches a closed coil. Determine near-face pole and current from the magnet-side view.
Give me a hint
Choose the interaction opposing approach.
Compare my reasoning
- Repulsion opposes approach.
- The near face is north.
- Its current is anticlockwise from the stated view.
North face; anticlockwise from the magnet side.
Look for these in your work
- Explain opposition.
- State the view.
A north pole withdraws from the same closed coil. Determine face and current from the same view.
Give me a hint
Choose the interaction opposing separation.
Compare my reasoning
- Attraction opposes withdrawal.
- The near face becomes south.
- Its current is clockwise from the stated view.
South face; clockwise from the magnet side.
Look for these in your work
- Explain attraction.
- Keep the viewing side unchanged.
A south pole approaches, then withdraws from a closed coil. Give near-face poles and current senses from the magnet side.
Give me a hint
Apply opposition separately to approach and separation.
Compare my reasoning
- Approach requires a south face, repelling it.
- Withdrawal requires a north face, attracting it.
- Current is clockwise on approach and anticlockwise on withdrawal.
Approach: south/clockwise; withdrawal: north/anticlockwise from the magnet side.
Look for these in your work
- Evaluate each change.
- Keep the current convention explicit.
Common mistakes
- Oppose the change, not merely the field.
- Name the viewing side.
- Current-produced opposition requires a closed path.
What can you explain now?
A north pole withdraws from a closed coil. What should the near coil face do?
Compare with the explanation
Become south and attract it
Attraction opposes the increasing separation that causes the field-linking change.
After trying it yourself, choose your next review. This is your self-assessment.
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Make it stick
Predict opposition to the actual change, then translate near-face pole to current using an explicit viewing direction.
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