PhysicsICSE Class 9 · Magnetism

Magnetic Materials, Induced Magnetism and Field Lines: Reasoning Questions (ICSE Class 9)

Updated 17 October 2026 · Fact-checked

A magnet repels a like pole, but attracts an unlike pole and also unmagnetised iron, so repulsion is the sure test of magnetism. A magnetic material near a pole acquires an unlike pole at its near end by induction, and only then is attracted. Field lines run N to S outside a magnet, S to N inside, never cross and are crowded where the field is strong.

Understand Magnetic Materials, Induced Magnetism and Magnetic Field Lines

Magnetic and non-magnetic materials. Iron, steel, nickel and cobalt are attracted by a magnet and can be magnetised; wood, plastic, copper, aluminium and glass cannot. A freely suspended bar magnet settles along north–south; its two ends are the poles. Like poles repel; unlike poles attract.

Sure test. Attraction is not enough (a magnet also attracts unmagnetised iron). A bar is surely a magnet only if it repels the like pole of a known magnet.

Induced magnetism. A magnetic material near a magnet becomes a temporary magnet: the end nearer the magnet’s pole gets the unlike pole, the far end the like pole. Soft iron is magnetised and demagnetised easily (temporary magnet; electromagnets); steel keeps its magnetism (permanent magnets, compass needles).

Induction precedes attraction. A magnet attracts iron only after inducing magnetism:
1. the near end of the iron gets an unlike pole;
2. the unlike poles attract; the like pole at the far end is repelled, but it is farther away and the attraction wins;
3. so every magnetic material is attracted by either pole, and non-magnetic materials, which cannot be magnetised, are not.

Chain of nails. If the N pole of a magnet touches the top of nail 1, and nail 2 hangs from nail 1 and nail 3 from nail 2, each nail has an S pole at its top (nearer the N source) and an N pole at its bottom. When the magnet is removed the soft iron nails lose their magnetism and fall apart.

Magnetic field and field lines. A magnetic field line is the path of a free north pole; the tangent gives the field direction.

Outside a magnet lines run from N to S; inside they run from S to N, forming closed loops.
Lines never intersect (the field cannot have two directions at a point).
Lines are crowded where the field is strong (near poles), spread out where weak.
Parallel, equally spaced lines show a uniform field.

Field between magnets.

*Unlike poles facing each other:* lines run straight from N to S across the gap; the field is nearly uniform between the poles.
*Like poles facing each other:* the lines bend away and do not cross; between the poles there is a point (a neutral point) where the two fields cancel. If one magnet is stronger, this point lies nearer the weaker pole.

Tracing. Use a small plotting compass or iron filings: the filings become magnetised by induction and set along the lines.

Magnetic Materials, Induced Magnetism and Magnetic Field Lines: formulas and key facts

Pole rule: $like poles repel; unlike poles attract$; Repulsion is the sure test.
Induction rule: $near end of iron gets the unlike pole$; Then attraction follows.
Field lines: $N \to S (outside); S \to N (inside)$; Closed loops; never cross.

How to solve Magnetic Materials, Induced Magnetism and Magnetic Field Lines questions

For pole-labelling questions, work from the source pole outward.

1Identify the source magnet and the pole nearest to the first piece of iron.
2Label the near end of that piece with the unlike pole and the far end with the like pole.
3Repeat for the next piece, treating the previous far end as the new source.
4For field patterns, draw lines from N to S outside, never crossing, crowded near poles.
5Say "temporary magnet" for soft iron and "permanent magnet" for steel.

Magnetic Materials, Induced Magnetism and Magnetic Field Lines in real life

Each concept, met in an everyday situation. Read the situation, try the problem, then check the solution. The one-line hook is what to remember.

Picking up pins

Suppose you touch a magnet’s N pole to a soft iron pin and the pin then holds a second soft iron pin hanging from it.

Explain what happens and why the second pin falls when the magnet is pulled away.

Try it first, then show the solutionSolution

The first pin is magnetised by induction: S pole at the top, N pole at the bottom; the second pin is magnetised in the same way.
Removing the magnet removes the induction; the soft pins lose most of their magnetism and drop.

Answer: Induced (temporary) magnetism; the chain breaks when the magnet is removed.

Memory hook: No magnet, no induction.

Tricks to remember Magnetic Materials, Induced Magnetism and Magnetic Field Lines

Short memory aids. Say each one aloud once, then use it on a question the same day.

Repel to be sure
Only repulsion proves magnetism.
Use it when: Test questions.
Near end opposite
Near end of iron gets the opposite pole of the magnet.
Use it when: Induced poles.
Lines never cross
Crossing lines would give two directions at one point.
Use it when: Field line properties.

Magnetic Materials, Induced Magnetism and Magnetic Field Lines: solved examples

Ordered from board level to HOTS. Try each one before you open the solution.

Example 1: Sure test · 1 mark · MCQBoard level

The sure test for a bar being a magnet is that it:
(a) attracts iron filings
(b) repels the like pole of a magnet
(c) attracts the pole of a magnet
(d) attracts a steel needle

Try it first, then show the solutionSolution

Unmagnetised iron is attracted by a magnet but never repelled, so only repulsion proves the bar is a magnet.

Answer: (b)

Example 2: Iron near a pole · 2 marks · Short answerBoard level

A soft iron nail is brought near the S pole of a bar magnet. Name the poles formed at the two ends of the nail and say what happens when the magnet is removed.

Try it first, then show the solutionSolution

The end nearer the S pole becomes a N pole and the far end becomes a S pole (induced magnetism). (1)
On removing the magnet the soft iron nail loses most of its magnetism. (1)

Answer: Near end N, far end S; the nail demagnetises

Example 3: Chain of nails · 3 marks · Short answerHarder board level

The N pole of a bar magnet touches the top of iron nail 1. Nail 2 hangs from nail 1 and nail 3 from nail 2. Give the poles at the top and bottom of each nail and explain why nail 2 is attracted.

Try it first, then show the solutionSolution

Nail 1: top S, bottom N. (1)
Nail 2: top S, bottom N; nail 3: top S, bottom N (each is induced by the nail above). (1)
Nail 2 is attracted because the N pole at the bottom of nail 1 induces an S pole at its top; unlike poles attract. (1)

Answer: Each nail: top S, bottom N

Example 4: Identifying the magnet · 3 marks · Short answerHarder board level

Bars A and B look identical; one is a magnet and the other soft iron. Describe a test with only these two bars to decide which is the magnet.

Try it first, then show the solutionSolution

Touch one end of A to the middle of B. A magnet’s middle has little attraction, but its ends do. (1)
If A sticks strongly to B’s middle, A is the magnet (its end attracts iron at B’s middle). (1)
If there is little or no attraction, then B is the magnet (the middle of a magnet attracts weakly) and A is the iron; reverse the roles to confirm. (1)

Answer: End of the magnet to the middle of the iron attracts; end of the iron to the middle of the magnet hardly does

Example 5: Two magnets side by side · 4 marks · Case-basedHOTS / competency

Two identical bar magnets lie in a line with their N poles facing each other, 6 cm apart.
(a) Describe the field lines between the poles.
(b) Where is the neutral point, and what is the net field there?
(c) If the right magnet is replaced by a stronger one, where does the neutral point move?
(d) If the right magnet is turned so that unlike poles face each other, describe the field between them.

Try it first, then show the solutionSolution

(a) Lines from both N poles bend away from each other and do not cross. (1)
(b) Midway between the poles; the fields are equal and opposite, so the net field is zero. (1)
(c) Nearer the weaker magnet. (1)
(d) Lines run straight from the N pole of one to the S pole of the other; a nearly uniform field. (1)

Answer: (a) lines repel, no crossing (b) midway; zero (c) towards the weaker magnet (d) straight lines, uniform

Where students lose marks in Magnetic Materials, Induced Magnetism and Magnetic Field Lines

The slips examiners see most often, and what to write instead.

Mistake: Attraction given as the test for a magnet
Iron is also attracted.
Wrong working
It attracts iron filings, so it is a magnet.
Right working
It repels a like pole.
Do this: Say "repulsion".
Usually costs: 1 mark.
Mistake: Same pole induced at the near end
The near end gets the unlike pole.
Wrong working
Near end N for a N pole of the magnet.
Right working
Near end S.
Do this: Opposite, then attraction.
Usually costs: 1 to 2 marks.
Mistake: Field lines crossing in a diagram
Field lines never intersect.
Wrong working
Lines drawn crossing between like poles.
Right working
Lines bend away without crossing.
Do this: Draw arrows and keep them apart.
Usually costs: Diagram mark.

Exam tips

Draw arrows on field lines and label N and S.
Name the induced poles at both ends of each piece of iron.
Quote "induction precedes attraction" with the two-step explanation.
Mention soft iron (temporary) and steel (permanent) when asked about retention.

Practice questions on Magnetic Materials, Induced Magnetism and Magnetic Field Lines

Write each answer on paper first. Open the hint only if you are stuck, and the answer only when you have finished.

Q1 · 1 mark · MCQBoard level
Which of the following is NOT attracted by a magnet?
(a) nickel
(b) cobalt
(c) aluminium
(d) steel
Hint
Non-magnetic materials.
Answer
(c) aluminium
Q2 · 1 mark · Very short answerBoard level
In which direction do the magnetic field lines run inside a bar magnet?
Hint
Closed loops.
Answer
From the S pole to the N pole.
Q3 · 2 marks · Short answerHarder board level
Why does a magnet attract a piece of iron from a distance but never a piece of wood?
Hint
Think of induction.
Answer
Iron is magnetised by induction (an unlike pole forms at the near end), which is attracted; wood cannot be magnetised, so no induction and no attraction occurs.
Q4 · 3 marks · Short answerHarder board level
Why can two magnetic field lines never intersect? Why are the lines closed loops?
Hint
Direction at a point.
Answer
If they crossed, a compass at the crossing point would have to point in two directions. Outside the magnet the lines run N to S and inside S to N, so each line continues as a closed loop.
Q5 · 2 marks · Assertion-reasonHarder board level
Assertion (A): Both poles of a magnet attract a piece of soft iron.
Reason (R): Each pole of the magnet induces an unlike pole at the near end of the iron.
(a) Both true, R explains A.
(b) Both true, R does not explain A.
(c) A true, R false.
(d) A false, R true.
Hint
Induction precedes attraction.
Answer
(a)
Q6 · 3 marks · Short answerHOTS / competency
A steel needle and a soft iron needle are stroked with a magnet. Which one is a better choice for (a) a compass needle and (b) the core of an electromagnet? Give the property in each case.
Hint
Think of retaining the magnetism.
Answer
(a) The steel needle: it retains its magnetism (permanent magnet). (b) Soft iron: it is magnetised and demagnetised easily, so the magnetism can be switched on and off.

Test your recall

Answer in your head or on paper first, then open the card. Pulling an answer out of memory makes it stick far better than re-reading.

1.Sure test of magnetism?Show answer
Repulsion.
2.Induced pole at the near end?Show answer
The unlike pole.
3.Where are magnetic field lines most crowded?Show answer
Near the poles, where the field is strongest.
4.Can field lines cross?Show answer
No.
5.Which material is a temporary magnet?Show answer
Soft iron.

Magnetic Materials, Induced Magnetism and Magnetic Field Lines: frequently asked questions

What is induced magnetism?

The magnetism produced in a magnetic material when it is placed near or in contact with a magnet; the near end gets the unlike pole.

What does "induction precedes attraction" mean?

A magnet attracts iron only after it has induced an unlike pole at the near end of the iron.

What are the properties of magnetic field lines?

They run from N to S outside the magnet and S to N inside, form closed loops, never intersect and are crowded where the field is strong.