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Tamil Nadu (TNBSE)Class 8 Science★ 4-7 marks in the TN Class 8 annual exam through book-back MCQs and short answers

Magnetism

Samacheer Kalvi (TN State Board) Class 8 Science — Physics Chapter 7, Magnetism. Magnetic materials and poles, natural, artificial, permanent and temporary magnets, the magnetic field and the Earth as a magnet, the magnetic compass, the electromagnet and its uses (including Maglev and MRI), and the iron ores. Notes with the actual book-back questions, common mistakes and quick revision.

⏱ 16 min readEasy difficulty✓ Free · NCERT-aligned

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By the end of this chapter you'll be able to…

1Identify magnetic materials and the pole rule
2Classify magnets (natural/artificial, permanent/temporary)
3Explain the Earth's magnetic field and the compass
4Describe the electromagnet and its uses
5Name the iron ores

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Why this chapter matters

Magnetism explains compasses, electromagnets and modern machines from Maglev trains to MRI scanners. Magnet types, the Earth's field and electromagnet uses are directly tested book-back content in the TN Class 8 exam.

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A 5-minute refresher here will save you 30 minutes of confusion below.

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Class 6 — Fun with magnets

Magnetic and non-magnetic materials.

Magnetism — Class 8 Science (Samacheer Kalvi)

TN State Board (Samacheer Kalvi) Class 8 Science, Physics — Chapter 7. Magnets, poles, fields and their uses.

1. About this chapter

This chapter covers magnetic materials and poles, types of magnets, the magnetic field and the Earth as a magnet, the compass, the electromagnet and its uses, and the iron ores.

2. Magnetic materials, poles and types

A magnet attracts magnetic materials — iron, steel, nickel and cobalt.
Every magnet has two poles, north (N) and south (S); like poles repel, unlike poles attract; poles cannot be separated.
Natural magnet: lodestone (magnetite). Artificial magnets: bar, U-shaped, horseshoe, cylindrical, disc, ring and electromagnets.
Permanent magnets (e.g., neodymium, alnico) keep their magnetism; temporary magnets are magnetic only for a while.

3. Magnetic field, Earth and the compass

The magnetic field is the region around a magnet where its force acts, shown by field lines from N to S.
The Earth behaves like a giant bar magnet, so its magnetic field resembles that of a bar magnet.
A compass needle is a tiny pivoted magnet that points north–south; a compass is used for navigation, detecting a magnetic field and plotting magnetic field lines.

4. Electromagnet, uses and iron ores

An electromagnet is made by passing current through a coil on an iron core; it is magnetic only while current flows and is stronger with more turns and more current.
Uses: electric bell, electric motor, loudspeaker, microphone, Maglev train (floats above the track), magnetic conveyor belts (sorting magnetic scrap), and MRI (Magnetic Resonance Imaging) in hospitals.
Iron ores: Hematite (≈69% iron), Magnetite (≈72.4% iron) and Siderite (≈48.2% iron).

5. Worked examples

Example 1. What does a magnet attract? Magnetic materials such as iron and steel.

Example 2. The Earth's magnetic field resembles that of what? An imaginary bar magnet.

Example 3. Expand MRI. Magnetic Resonance Imaging.

6. Book-back questions (Samacheer Kalvi)

I. Choose the correct answer

A magnet attracts — (a) wood / (b) plastic / (c) iron and steel. Ans: (c) iron and steel.
An example of a permanent magnet is — (a) soft iron / (b) neodymium. Ans: (b) neodymium.
The south pole of a bar magnet and the north pole of a U-shaped magnet will — (a) attract each other / (b) repel. Ans: (a) attract.
The Earth's magnetic field resembles that of an imaginary — (a) horseshoe / (b) bar magnet. Ans: (b) bar magnet.
MRI stands for — (a) Magnetic Resonance Imaging.
A compass is used for — plotting magnetic lines, detecting a magnetic field, navigation → (d) all of these.

II. Answer briefly 7. Name the three iron ores. (Hematite, magnetite, siderite.) 8. Give two uses of an electromagnet. (Electric bell, Maglev train — also motors, loudspeakers, MRI, conveyors.)

7. Common mistakes

Mistake: Thinking a single magnetic pole can exist. Fix: Poles always come in pairs (N and S).
Mistake: Saying all metals are magnetic. Fix: Only iron, steel, nickel and cobalt are strongly magnetic.
Mistake: Treating an electromagnet as a permanent magnet. Fix: It is magnetic only while current flows.

8. Quick revision

Physics Ch 7 · magnets, poles, field, electromagnet, ores.
Magnets attract iron/steel/nickel/cobalt; like poles repel, unlike attract.
Permanent magnets (neodymium); artificial magnets: bar, U-shaped, horseshoe, ring, electromagnet.
Earth's field resembles a bar magnet; compass for navigation/detection/plotting.
Electromagnet uses: bell, motor, loudspeaker, Maglev, conveyor, MRI; iron ores: hematite, magnetite, siderite.

Key formulas & results

Everything you need to memorise, in one card. Screenshot this for revision.

Pole rule

like poles repel; unlike attract

Two inseparable poles.

Earth's field

resembles a bar magnet

Basis of the compass.

Electromagnet

current in a coil on an iron core

Magnetic only while current flows.

Iron ores

hematite (69%), magnetite (72.4%), siderite (48.2%)

Percentage of iron.

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Common mistakes & fixes

These are the exact errors that cost students marks in board exams. Read them once, save yourself the trouble.

WATCH OUT

✗ Thinking a single magnetic pole can exist

✓ Poles always come in pairs (N and S).

WATCH OUT

✗ Saying all metals are magnetic

✓ Only iron, steel, nickel and cobalt are strongly magnetic.

WATCH OUT

✗ Treating an electromagnet as a permanent magnet

✓ It is magnetic only while current flows.

NCERT exercises (with solutions)

Every NCERT exercise from this chapter — what it covers and how many questions to expect.

Choose the correct answer

Book-back MCQs on magnetic materials, permanent magnets, Earth's field, MRI and the compass.

Questions

Answer briefly

Iron ores, uses of electromagnets, the compass needle.

Questions

Answer in detail

Electromagnet and its applications.

Questions

Practice problems

Try each one yourself before tapping "Show solution". Active recall > rereading.

Q1EASY· MCQ

A magnet attracts (a) wood (b) plastic (c) iron and steel.

▶ Show solution

(c) iron and steel.

Q2EASY· MCQ

An example of a permanent magnet is ____.

▶ Show solution

neodymium.

Q3EASY· MCQ

The Earth's magnetic field resembles that of an imaginary ____.

▶ Show solution

bar magnet.

Q4EASY· MCQ

Expand MRI.

▶ Show solution

Magnetic Resonance Imaging.

Q5EASY· Answer briefly

Name the three iron ores.

▶ Show solution

Hematite, magnetite and siderite.

Q6MEDIUM· Answer briefly

Give two uses of an electromagnet.

▶ Show solution

Electric bell and Maglev train (also motors, loudspeakers, MRI and magnetic conveyors).

5-minute revision

The whole chapter, distilled. Read this the night before the exam.

•Physics Chapter 7 of Samacheer Kalvi Class 8 Science.
•Magnets attract iron/steel/nickel/cobalt; like poles repel, unlike attract.
•Permanent magnets (neodymium); artificial: bar, U-shaped, horseshoe, ring, electromagnet.
•Earth's field resembles a bar magnet; compass for navigation/detection/plotting.
•Electromagnet uses: bell, motor, loudspeaker, Maglev, conveyor, MRI.
•Iron ores: hematite (69%), magnetite (72.4%), siderite (48.2%).

Tamil Nadu (TNBSE) marks blueprint

Where the marks come from in this chapter — so you can plan your prep.

Typical chapter weightage: 4-7 marks across book-back MCQ and short answers

Question type	Marks each	Typical count	What it tests
MCQ	1	2-4	Materials, magnets, Earth's field, MRI
Short Answer	2-3	1-2	Iron ores, electromagnet uses
Long Answer	3-5	0-1	Electromagnet and applications

Prep strategy

Learn the pole rule and magnetic materials
Note permanent magnets (neodymium) and types
Remember Earth's field resembles a bar magnet
List electromagnet uses and the three iron ores

Where this shows up in the real world

This chapter isn't just an exam topic — it lives in the world around you.

Navigation

The magnetic compass shows direction.

Machines and transport

Electromagnets run motors, loudspeakers and Maglev trains.

Medicine

MRI scanners use strong magnetic fields to image the body.

Exam strategy

Battle-tested tips from teachers and toppers for this chapter.

State the pole rule and magnetic metals
Recall Earth's field = bar magnet
List electromagnet uses
Name the three iron ores with iron percentage

Going beyond the textbook

For olympiad aspirants and curious learners — topics that build on this chapter.

Explain how to make a temporary magnet by the single-touch method.
Compare the iron content of hematite, magnetite and siderite.

Where else this chapter is tested

CBSE board isn't the only one — other exams test this chapter too.

TN Class 8 Annual ExamHigh

Foundation / NMMS ScienceMedium

School unit testsHigh

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Questions students ask

The real ones — pulled from the Q&A community and tutor sessions.

Powerful electromagnets make the train float just above the track, removing friction so it can move very fast.

It is a tiny pivoted magnet that aligns itself with the Earth's magnetic field, whose poles lie near the geographic north and south.

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