Explain induced magnetism in soft iron
Track the temporary poles formed in a nearby iron object and explain its attraction without contact.
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
- Recall the pole force rules.
- Identify initially unmagnetised magnetic material.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
Which pair attracts?
What you will learn
- Describe magnetisation induced by a nearby magnet.
- Identify the near and far induced poles in a soft-iron model.
Induce opposite poles
A magnetic material can become magnetised when placed in a magnetic field. Bring a north pole near one end of a soft-iron bar: the near end becomes south and the far end becomes north. The near unlike poles attract. Contact is not required for this induction.
If the inducing pole is south, the near end becomes north and the far end south. The initially unmagnetised piece can therefore be attracted by either inducing pole. Magnetised means it has acquired an organised magnetic response; it does not mean an electrical charge was transferred into it.
Remove the inducing influence
Soft iron is useful when an induced magnet should be temporary. Much of its induced magnetism is lost when the external field is removed. A chain of iron pieces can consequently separate when the inducing magnet is taken away.
The amount retained depends on the material and its history. Use soft iron for the stated temporary model rather than asserting that every magnetic material instantly loses all magnetisation. This induction is different from electromagnetic induction of a voltage, which belongs to a later section.
Sources for this lesson
Pause and explain
A south pole approaches the near end of soft iron. What pole is induced at that near end?
Worked example
A north pole approaches the left end of an initially unmagnetised soft-iron bar. Name the induced ends.
Show the worked solution
- The near end must be unlike the inducing pole.
- The left near end becomes S.
- The right far end becomes N.
Answer Near end S, far end N; the bar is attracted toward the inducing magnet.
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.
Name the induced near and far poles when an N pole approaches soft iron.
Give me a hint
Make the near pole unlike and use the opposite pole at the far end.
Compare my reasoning
- The inducing pole is N.
- The near end is S.
- The far end is N.
Near S; far N.
Look for these in your work
- Read near versus far.
- Include both induced ends.
Repeat for an S inducing pole and state the force direction.
Give me a hint
Reverse both induced pole labels when the source pole reverses.
Compare my reasoning
- The near end becomes N.
- The far end becomes S.
- The iron is attracted toward the source magnet.
Near N; far S; attraction toward the source.
Look for these in your work
- Reverse the pole labels.
- State attraction.
An induced soft-iron chain falls apart when the source magnet is removed. Explain the change.
Give me a hint
Connect loss of the inducing field to temporary magnetisation.
Compare my reasoning
- The source supplied the inducing field.
- Soft iron loses much of its induced magnetism after removal.
- The magnetic support between pieces becomes too weak to hold the chain.
Removal weakens the temporary magnetisation and the supporting attraction.
Look for these in your work
- Name the inducing influence.
- Use the stated soft-iron model.
Common mistakes
- The near induced pole is unlike the source pole.
- Induction need not require contact.
- Magnetic induction here does not mean charging.
What can you explain now?
Can an unmagnetised soft-iron bar be attracted by either pole?
Compare with the explanation
Yes.
The near induced end is opposite to whichever source pole is presented.
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Make it stick
Track induced poles and explain attraction and loss of temporary magnetism.
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.