PhysicsICSE Class 9 · Magnetism

The Earth's Magnetic Field, the Compass and Neutral Points: Axial and Equatorial Cases (ICSE Class 9)

Updated 17 October 2026 · Fact-checked

The Earth behaves like a huge bar magnet with its magnetic S pole near geographic north, so the N pole of a compass points north. A neutral point is where the field of a bar magnet cancels the Earth's horizontal field; for a magnet with N pole pointing geographic north the neutral points lie on the equatorial line, and with N pole pointing south they lie on the axial line.

Understand The Earth's Magnetic Field, the Compass and Neutral Points

The Earth as a magnet. Evidence: a freely suspended magnet rests in the north–south direction; a soft iron bar kept along north–south for a long time becomes magnetised; neutral points are found near bar magnets. The Earth acts as if a huge bar magnet lay inside it with its S pole near geographic north and its N pole near geographic south. That is why the N pole of a compass needle points north.

The magnetic compass. A small magnetised needle pivoted so that it swings freely in a horizontal plane above a scale. It aligns along the Earth’s horizontal field. It must be kept away from iron objects and magnets.

Earth’s field in a laboratory. Over a small region the Earth’s horizontal field is uniform: parallel, equally spaced lines pointing from geographic south to north.

Neutral point. When a bar magnet is placed on a table, its non-uniform field adds to the Earth’s uniform 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 does not settle in a single direction.

Two standard cases (magnet along the north–south line, i.e. the magnetic meridian):

Orientation of the magnet	Where the neutral points lie	Why
N pole pointing geographic north	On the equatorial line (the perpendicular bisector), one on each side (east and west)	On the equatorial line the magnet’s field points from N to S, i.e. southward, opposite to the Earth’s northward field
N pole pointing geographic south	On the axial line, one beyond each pole (north and south of the magnet)	Beyond each pole the magnet’s field now points southward, opposite to the Earth’s northward field

Features. The two neutral points are symmetrical about the centre of the magnet. A weaker magnet has its neutral points closer to it; a stronger one farther away. If the magnet is turned through $18 0^{\circ}$ , the neutral points move from one line to the other.

Locating them. Place a plotting compass on the equatorial (or axial) line and move it until the needle, when turned to any direction, stays there without swinging back. That is the neutral point. Mark it and repeat on the other side.

The Earth's Magnetic Field, the Compass and Neutral Points: formulas and key facts

Earth as a magnet: $magnetic S pole near geographic N; N pole near geographic S$; Compass N points north.
Neutral point: $B_{ma g n e t} = B_{E a r t h (h or i z o n t a l)}, opposite in direction$; Net field zero.
Cases: $N north : equatorial line; N south : axial line$; Two neutral points in each case.

How to solve The Earth's Magnetic Field, the Compass and Neutral Points questions

Compare directions of the magnet’s field and the Earth’s field.

1Draw the magnet with its poles labelled and the north direction marked.
2Draw the Earth’s field as a uniform arrow pointing north.
3Find where the magnet’s field points opposite to this arrow.
4Check the points are symmetric about the centre of the magnet.
5Name the line (axial or equatorial) and the two sides.

The Earth's Magnetic Field, the Compass and Neutral Points 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.

Using a compass near a steel desk

Suppose you place a compass on a steel desk beside a bar magnet used by your classmates.

Why is the reading unreliable?

Try it first, then show the solutionSolution

The needle feels the Earth’s field plus the field of the nearby magnet and of the magnetised steel.
Only far from magnets and iron does it show the Earth’s field alone.

Answer: Extra magnetic fields disturb the compass.

Memory hook: Compass needs a clean field.

Tricks to remember The Earth's Magnetic Field, the Compass and Neutral Points

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

Earth’s S is up north
The Earth’s magnetic S pole is near geographic north, which attracts a compass N pole.
Use it when: Pole questions.
North on the equator, south on the axis
N pole points north: neutral points on the equator. N pole points south: on the axis.
Use it when: Neutral point cases.
Net zero means the needle is free
At a neutral point a compass can rest in any direction.
Use it when: Identification of neutral points.

The Earth's Magnetic Field, the Compass and Neutral Points: solved examples

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

Example 1: Pole of the Earth · 1 mark · MCQBoard level

The magnetic pole of the Earth that lies near the geographic north is a:
(a) north magnetic pole
(b) south magnetic pole
(c) neutral pole
(d) both poles

Try it first, then show the solutionSolution

The N pole of a compass points north, so the Earth’s pole near geographic north must be a S pole.

Answer: (b) south magnetic pole

Example 2: Why a compass points north · 2 marks · Short answerBoard level

Explain why the N pole of a freely pivoted compass needle points towards geographic north.

Try it first, then show the solutionSolution

The Earth behaves like a bar magnet with its magnetic S pole near geographic north. (1)
The N pole of the needle is attracted to this S pole (unlike poles attract) and so points north. (1)

Answer: Needle N pole is attracted by the Earth’s S pole in the north

Example 3: Why the equatorial line · 3 marks · Short answerHarder board level

A bar magnet lies on a table along the magnetic meridian with its N pole pointing geographic north. Explain why the neutral points lie on its equatorial line.

Try it first, then show the solutionSolution

On the equatorial line, the magnet’s field points from its N end towards its S end, i.e. towards the south. (1)
The Earth’s horizontal field points north, so the two fields are opposite at these points. (1)
At the point where their magnitudes are equal the net field is zero: there are two such points, one on each side of the magnet (east and west). (1)

Answer: Magnet’s field (southward) opposes the Earth’s (northward) on the equatorial line

Example 4: Compass on the axis · 3 marks · Short answerHarder board level

A bar magnet lies along the magnetic meridian with its N pole pointing geographic north. A compass is placed on the axial line beyond the N pole and another beyond the S pole. In which direction does each needle point, compared with the Earth’s field alone?

Try it first, then show the solutionSolution

Beyond the N pole the magnet’s field points away from N, i.e. northwards, the same as the Earth’s field. (1)
Beyond the S pole the magnet’s field points towards S, i.e. northwards again. (1)
In both places the two fields add, so each needle points north (more firmly than far from the magnet); there is no neutral point on the axis for this orientation. (1)

Answer: Both point north; the fields add

Example 5: A laboratory activity · 4 marks · Case-basedHOTS / competency

A bar magnet lies on a sheet with its N pole pointing geographic south. Two neutral points P and Q are found on the axial line, both 12 cm from the centre of the magnet.
(a) On which side of the magnet is each point?
(b) Find the distance PQ.
(c) What does a compass do at P?
(d) The magnet is replaced by a weaker one. Where do the neutral points move?

Try it first, then show the solutionSolution

(a) One beyond each pole (north and south of the magnet) on the axis. (1)
(b) $P Q = 12 + 12 = 24$ cm (symmetric about the centre). (1)
(c) It does not settle in one direction; the net field is zero. (1)
(d) Closer to the magnet, because the magnet’s field is weaker and cancels the Earth’s at a smaller distance. (1)

Answer: (a) beyond each pole on the axis (b) 24 cm (c) no steady direction (d) closer

Where students lose marks in The Earth's Magnetic Field, the Compass and Neutral Points

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

Mistake: Earth’s pole near geographic north called north pole
It is a S pole.
Wrong working
The Earth’s magnetic N pole is near geographic north.
Right working
The Earth’s magnetic S pole is near geographic north.
Do this: Compass N is attracted to S.
Usually costs: 1 mark.
Mistake: Neutral point called a place where the Earth’s field is zero
It is where the net field is zero.
Wrong working
The Earth’s field is zero at the neutral point.
Right working
The magnet’s field is equal and opposite to the Earth’s horizontal field.
Do this: Say "net field is zero".
Usually costs: 1 mark.
Mistake: Wrong line chosen for the neutral points
N pointing north gives equatorial; N pointing south gives axial.
Wrong working
N pole north: axial line.
Right working
N pole north: equatorial line.
Do this: Remember: north-equator, south-axis.
Usually costs: 2 marks.

Exam tips

State the orientation of the magnet before naming the line of neutral points.
Give the direction of both fields at the neutral point.
Write "the net field is zero" for a neutral point.
Mention that a compass can point in any direction at a neutral point.

Practice questions on The Earth's Magnetic Field, the Compass and Neutral Points

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
A freely suspended bar magnet comes to rest:
(a) east–west
(b) north–south
(c) in any direction
(d) vertically only
Hint
Evidence of Earth’s magnetism.
Answer
(b) north–south
Q2 · 1 mark · Very short answerBoard level
In which direction does the Earth’s horizontal magnetic field point in a laboratory?
Hint
Think of the compass N pole.
Answer
From geographic south to north.
Q3 · 2 marks · Short answerHarder board level
Describe how you would locate the neutral points of a bar magnet with a plotting compass.
Hint
Look for the point where the needle has no preferred direction.
Answer
Place the magnet with its axis along the north–south line. Move the plotting compass along the correct line (equatorial or axial); at the neutral point the needle turns freely and rests in any direction. Mark the point and repeat on the other side.
Q4 · 3 marks · Short answerHarder board level
Explain why the field of a bar magnet and the Earth’s field combine to give a neutral point at a particular distance, and not at the pole.
Hint
Near the pole the magnet’s field is much larger.
Answer
Close to the magnet its field is much stronger than the Earth’s field, so the two cannot cancel. As one moves farther the magnet’s field falls until, at a certain distance and direction, it equals the Earth’s horizontal field and is opposite in direction. That is the neutral point.
Q5 · 2 marks · Assertion-reasonHarder board level
Assertion (A): The Earth’s magnetic south pole lies near the geographic north.
Reason (R): The N pole of a freely suspended compass needle points towards the geographic north.
(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
Unlike poles attract.
Answer
(a)
Q6 · 3 marks · Short answerHOTS / competency
A student first places a bar magnet with its N pole pointing geographic north and finds two neutral points on the equatorial line. She then turns the magnet through 180° so that its N pole points south. Predict where the neutral points will be now and justify with directions of the fields.
Hint
Reverse the magnet’s field direction.
Answer
They move to the axial line, one beyond each pole. Reversing the magnet reverses its field: on the equatorial line it now points northward (same as the Earth’s), so no cancellation there; on the axial line, beyond the poles, the magnet’s field now points southward, opposite to the Earth’s northward field, so cancellation is possible.

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.Earth’s pole near geographic north?Show answer
A magnetic S pole.
2.Neutral point?Show answer
A point where the magnet’s field cancels the Earth’s horizontal field.
3.N pole pointing north: neutral points on?Show answer
The equatorial line.
4.N pole pointing south: neutral points on?Show answer
The axial line.
5.Number of neutral points?Show answer
Two, symmetrical about the magnet.

The Earth's Magnetic Field, the Compass and Neutral Points: frequently asked questions

Why does the compass needle point north?

The Earth behaves like a bar magnet with a magnetic S pole near geographic north, so the N pole of the needle is attracted toward it.

What is a neutral point?

A point where the field of a magnet is equal and opposite to the Earth’s horizontal field, so the resultant field is zero.

Where are the neutral points of a bar magnet?

On the equatorial line when its N pole points geographic north, and on the axial line when its N pole points geographic south.