Magnetism ICSE Class 9: Induced Magnetism, Field Lines and Neutral Points

What Magnetism is about

Weightage: CISCE publishes no chapter weightage and no question-paper layout for ICSE Class 9 Physics. Class IX is examined by your school: one 80-mark paper of 2 hours plus 20 marks of internal assessment. Magnetism is in the 8. Electricity and Magnetism (ii) part of the 2028 syllabus.Source: CISCE ICSE 2028 Physics syllabus, Class IX

Key concepts

Magnetic and non-magnetic materials; poles

Magnetic materials are attracted by a magnet and can be magnetised: iron, steel, nickel, cobalt. Non-magnetic materials are not: wood, plastic, copper, aluminium, glass.

A bar magnet has two poles near its ends, where its effect is strongest. A freely suspended magnet comes to rest along the north–south direction; the end pointing north is its north pole (N).

Like poles repel; unlike poles attract.

Repulsion is the sure test of magnetism: a magnet attracts both an unlike pole and a piece of unmagnetised iron, but repels only a like pole of another magnet.

Worked example

Two identical-looking bars X and Y are given; one is a magnet. When the N pole of a known magnet is brought near one end of X, it is repelled. What can you conclude?

Try it first, then show the solutionSolution

1. Repulsion happens only between like poles.
2. So that end of X is a north pole, and X is a magnet.
3. Y is the unmagnetised bar.

Answer: X is the magnet; the end tested is its N pole.

Induced magnetism

When a magnetic material (such as a soft iron bar) is placed near or in contact with a magnet, it becomes a temporary magnet. This is magnetic induction, and the magnetism produced is induced magnetism.

The end of the iron nearer the magnet's pole gets the opposite (unlike) pole; the far end gets a like pole.

Soft iron gains and loses induced magnetism easily (temporary magnet; used in electromagnets); steel is harder to magnetise but keeps its magnetism (permanent magnet).

Example: a chain of iron nails hangs from a magnet, each nail magnetised by the one above it; when the magnet is removed, the nails fall apart.

Worked example

The N pole of a bar magnet is brought near end A of a soft iron bar AB. Name the poles induced at A and B.

Try it first, then show the solutionSolution

1. The near end gets the unlike pole: A becomes S.
2. The far end gets the like pole: B becomes N.

Answer: A: south pole; B: north pole

Induction precedes attraction

A magnet attracts a piece of iron only after inducing magnetism in it:
1. The magnet first induces an unlike pole on the near end of the iron.
2. The unlike poles attract each other.
3. The like pole induced at the far end is repelled, but it is further away, so the attraction is stronger and the iron is pulled in.

This is why we say induction precedes attraction. It also explains why only magnetic materials are attracted: non-magnetic materials cannot be magnetised by induction.

Worked example

Why does a magnet attract an iron nail but not a copper wire?

Try it first, then show the solutionSolution

1. Iron is magnetic: the magnet induces an unlike pole on the nearer end of the nail, which is then attracted.
2. Copper is non-magnetic: no magnetism is induced, so there is no attraction.

Answer: Induction happens in iron but not in copper.

Magnetic field lines and their properties

A magnetic field line is the path along which a free (isolated) north pole would tend to move. Its tangent at any point gives the direction of the field there (the direction a compass needle's N points).

Properties:

• Outside a magnet, field lines go from the N pole to the S pole; inside the magnet they go from S to N, so each line is a closed loop.
• Field lines never intersect (if they did, the field would have two directions at one point).
• They are crowded where the field is strong (near the poles) and spread out where it is weak.
• Parallel, equally spaced lines show a uniform field.

Field lines can be traced with a small plotting compass, or shown by sprinkling iron filings around a magnet.

Worked example

Why can two magnetic field lines never cross each other?

Try it first, then show the solutionSolution

1. At a crossing point there would be two tangents, i.e. two directions of the field.
2. A compass needle there would have to point two ways at once, which is impossible.

Answer: The field has only one direction at a point.

The Earth's magnetic field and the compass

Evidence that the Earth behaves like a magnet:

• a freely suspended magnet always comes to rest along the north–south direction;
• a soft iron bar buried in the ground along north–south for a long time becomes magnetised;
• neutral points are found when a bar magnet's field is combined with the Earth's (see below).

The Earth acts as if a huge bar magnet lay inside it with its S pole near the geographic north and its N pole near the geographic south. That is why the N pole of a compass points north.

A magnetic compass is a small magnetised needle pivoted to turn freely in a horizontal plane over a scale, used for finding directions.

Over the small area of a laboratory, the Earth's field is uniform: its horizontal field lines are parallel, equally spaced and point from geographic south to north.

Worked example

If the Earth behaves like a bar magnet, which of its magnetic poles is near the geographic North Pole? Explain using the compass.

Try it first, then show the solutionSolution

1. The N pole of a compass needle points to the geographic north.
2. Unlike poles attract, so a magnetic S pole must be near the geographic north.

Answer: A magnetic south pole.

Neutral points

Around a bar magnet on a table, its non-uniform field combines with the Earth's uniform horizontal field. A neutral point is a point where the magnet's field is equal and opposite to the Earth's horizontal field, so the net field is zero. A compass placed there points in any direction (it does not settle).

Two standard cases (magnet along the magnetic meridian):

• N pole of the magnet pointing geographic north: the two neutral points lie on the equatorial line (perpendicular bisector of the magnet), one on the east side and one on the west side.
• N pole pointing geographic south: the two neutral points lie on the axial line (the magnet's axis), one beyond each pole.

Neutral points are themselves evidence of the Earth's magnetic field.

Worked example

A bar magnet is placed with its N pole pointing towards geographic south. Where will the neutral points be, and why?

Try it first, then show the solutionSolution

1. Beyond the N pole (to the south), the magnet's field points south, while the Earth's points north: they can cancel on the axis.
2. Beyond the S pole (to the north), the magnet's field points south (towards S) and the Earth's north: they can cancel there too.
3. So the neutral points lie on the axial line, one beyond each pole.

Answer: On the axial line, beyond each pole.

Physics in real life: Magnetism

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.

Topics in this chapter

• The Earth's Magnetic Field, the Compass and Neutral Points
• Magnetic Materials, Induced Magnetism and Magnetic Field Lines

Magnetism formula sheet

Pole rule

$\text{like poles repel};\text{unlike poles attract}$

Repulsion is the sure test.

Induced pole

$N\text{near}\Rightarrow S\text{induced at near end}$

Like pole at the far end.

Field direction

$N\to S(\text{outside});S\to N(\text{inside})$

Closed loops.

Neutral point

$B_{magnet}=B_{Earth(horizontal)}\text{(opposite)}$

Net field zero.

Magnetism: diagrams to practise

Practise each one on paper: draw it from the checklist, then tick off every label.

How the school exam asks Magnetism

The question patterns to expect, and the method that works for each.

Tricks to remember Magnetism

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

• Opposites at the doorstep

  Induction puts the opposite pole at the near end, then the opposites attract.

  Use it when: Induced poles.

• Repel to reveal

  Only a magnet can repel a magnet, so repulsion reveals a magnet.

  Use it when: Sure test of a magnet.

• Out N, in S

  Outside, lines come out of N and go into S; inside the magnet they return S to N.

  Use it when: Field-line direction.

• North-north, neutral on the sides

  N pole facing north: neutral points to the sides (equatorial). N facing south: neutral points on the ends (axial).

  Use it when: Neutral points.

Magnetism: exam-level solved questions

Ordered from exam level to HOTS. Cover the solution, write your own, then compare step by step.

Case-study practice (Section B style)

Read the situation, then answer every part. In a school exam set on the board pattern this is a 8-mark question split into 2 + 3 + 3 marks.

Where the marks are

How a typical answer is split into step marks. Show every step: a right final answer alone rarely earns full marks.

Where students lose marks in Magnetism

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

• ✗Mistake: Wrong direction of field lines inside the magnet

  CISCE's 2025 ICSE Physics report (Class X) lists the direction of magnetic field lines inside and outside a magnet, and identifying a magnet's poles, among the topics candidates found difficult or confusing.

  Wrong working

  Arrows from S to N outside the magnet

  Right working

  Outside N → S; inside S → N (closed loops)

  ✓Do this: Check with a compass rule: its N end points along the field, away from N and towards S outside.

  Usually costs: 1 to 2 diagram marks.

• ✗Mistake: Neutral points on the wrong line

  Students mix up the two cases.

  ✓Do this: N towards north: equatorial; N towards south: axial.

  Usually costs: 1 to 2 marks.

• ✗Mistake: Using attraction to test for a magnet

  Attraction also happens between a magnet and unmagnetised iron.

  ✓Do this: Use repulsion as the sure test.

  Usually costs: 1 mark.

• ✗Mistake: Crossing or unlabelled field lines

  Field lines never cross, and lines without arrows show no direction.

  ✓Do this: Draw smooth, non-crossing lines with arrows on each.

  Usually costs: 1 mark.

• ✗Mistake: Same pole induced at the near end

  Induction gives the unlike pole at the near end.

  ✓Do this: Near end opposite, far end same.

  Usually costs: 1 mark.

Practice questions on Magnetism

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

1. Q1 · 1 mark · MCQExam level

   Which material is attracted by a magnet?
   (a) copper
   (b) aluminium
   (c) nickel
   (d) glass

   Hint

   Magnetic metals.

   Answer

   (c)

2. Q2 · 1 mark · MCQExam level

   Inside a bar magnet, magnetic field lines run:
   (a) from N to S
   (b) from S to N
   (c) nowhere
   (d) in circles around the magnet

   Hint

   Closed loops.

   Answer

   (b)

3. Q3 · 2 marks · Short answerExam level

   State two differences between a uniform and a non-uniform magnetic field, with one example of each.

   Hint

   Lines' shape and spacing.

   Answer

   Uniform: same strength and direction everywhere; parallel, equally spaced lines (the Earth's field in a room). Non-uniform: strength and/or direction vary; curved or unevenly spaced lines (field of a bar magnet).

4. Q4 · 1 mark · Assertion-reasonHarder exam level

   Assertion (A): An iron nail is attracted by both poles of a magnet.
   Reason (R): The pole of a magnet induces an unlike pole at the nearer end of the nail.
   (a) (A) is true and (R) is false.
   (b) (A) is false and (R) is true.
   (c) Both (A) and (R) are true, and (R) is the correct explanation for (A).
   (d) Both (A) and (R) are true, but (R) is not the correct explanation for (A).

   Hint

   Induction precedes attraction.

   Answer

   (c)

5. Q5 · 2 marks · Short answerHarder exam level

   How can you magnetise an iron bar using a bar magnet without touching it? Name the poles formed.

   Hint

   Induction.

   Answer

   Bring a pole of the magnet close to one end of the bar: magnetism is induced. If the N pole is near end A, A becomes S and the far end becomes N.

6. Q6 · 2 marks · Short answerExam level

   A compass needle placed at a point near a bar magnet does not settle in any particular direction. What is that point called, and what is the net magnetic field there?

   Hint

   Cancellation.

   Answer

   A neutral point; the net field is zero.

7. Q7 · 2 marks · Short answerHarder exam level

   Explain why field lines are crowded near the poles of a bar magnet.

   Hint

   Strength.

   Answer

   The field is strongest near the poles, and crowding of field lines represents a stronger field.

8. Q8 · 2 marks · Short answerHarder exam level

   Draw the field lines of the Earth in a small region and describe them.

   Hint

   Uniform field.

   Answer

   Parallel, equally spaced straight lines with arrows pointing from geographic south to geographic north (the horizontal component), showing a uniform field.

9. Q9 · 2 marks · Short answerHarder exam level

   Give a reason: a magnetic compass should not be kept near iron objects or magnets.

   Hint

   Local fields.

   Answer

   Iron gets magnetised by induction and magnets have their own fields; these disturb the field at the needle, so it no longer points along the Earth's field.

10. Q10 · 4 marks · Long answerHOTS / competency

    You have three identical-looking bars: one magnet, one iron, one aluminium. Using only the three bars, explain how you would identify each.

    Hint

    Repulsion, then attraction.

    Answer

    First, the aluminium bar is the one not attracted by either of the other two. Call the remaining bars X and Y; their ends attract each other. Now touch one end of X to the middle of Y. If they attract strongly, X is the magnet: its pole induces magnetism in the iron. If there is hardly any attraction, Y is the magnet, because the middle of a magnet has almost no magnetism and X (iron) has no poles of its own.

11. Q11 · 4 marks · Long answerHOTS / competency

    Draw the field pattern of a bar magnet with its N pole pointing geographic south and mark the neutral points. Explain why there are no neutral points on the equatorial line in this case.

    Hint

    Direction of the magnet's field on the equatorial line.

    Answer

    Neutral points lie on the axis beyond each pole. On the equatorial line the magnet's field points from N to S, i.e. now northwards, in the same direction as the Earth's field, so the two add and can never cancel there.

12. Q12 · 3 marks · Short answerHarder exam level

    Two compasses are placed at points P and Q near a bar magnet, P closer to a pole than Q. Which needle is affected more by the magnet, and how would the field lines at P and Q differ in a drawing?

    Hint

    Distance from the pole.

    Answer

    P, being closer to the pole where the field is stronger. Field lines are drawn closer together at P than at Q.

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. 1.What is induced magnetism?Show answer

   Temporary magnetism produced in a magnetic material near a magnet.

2. 2.What is the sure test of a magnet?Show answer

   Repulsion with a known magnet.

3. 3.Direction of field lines outside a magnet?Show answer

   From N pole to S pole.

4. 4.Do field lines ever intersect?Show answer

   No.

5. 5.What is a neutral point?Show answer

   A point where the net magnetic field is zero.

6. 6.Neutral points when N points north?Show answer

   On the equatorial line (east and west).

7. 7.Which magnetic pole is near the geographic north?Show answer

   A magnetic south pole.

8. 8.Is the Earth's field in a room uniform or non-uniform?Show answer

   Uniform.

Quick revision checklist

The night before the exam: can you do each of these without looking?

• ☐Can you name the induced poles on a soft iron bar?
• ☐Can you explain 'induction precedes attraction'?
• ☐Can you explain why repulsion is the sure test?
• ☐Can you list four properties of field lines?
• ☐Do your field lines go N to S outside and S to N inside?
• ☐Can you give evidence for the Earth's magnetic field?
• ☐Can you place neutral points for both orientations?

Magnetism: frequently asked questions