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Tamil Nadu (TNBSE)Class 9 Science★ 5-6 marks in assessments

Magnetism and Electromagnetism

Samacheer Kalvi (TN State Board) Class 9 Science — Physics Chapter 5, Magnetism and Electromagnetism. Magnetism and electricity are deeply linked. Electromagnetism explains how motors convert electricity into mechanical power, how generators produce electrical energy, and how transformers work. Notes, worked examples, common mistakes, and quick revision.

⏱ 20 min readHard difficulty✓ Free · NCERT-aligned

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The chapter at a glance

Every concept and exam-favourite branch — revisable in 5 minutes.

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Study Guide

Night-before notes

Key points, glossary and the questions most likely to show up.

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

1Describe magnetic field and magnetic lines of force
2State Fleming's Left-Hand and Right-Hand rules
3Explain the working of an electric motor
4Explain electromagnetic induction and electric generators

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Why this chapter matters

Magnetism and electricity are deeply linked. Electromagnetism explains how motors convert electricity into mechanical power, how generators produce electrical energy, and how transformers work.

Before you start — revise these

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

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Class 8 Science — Magnetism

Properties of permanent magnets.

Magnetism and Electromagnetism — Class 9 Science (Samacheer Kalvi)

TN State Board (Samacheer Kalvi) Class 9 Science, Physics — Chapter 5. Magnetism and electricity are deeply linked. Electromagnetism explains how motors convert electricity into mechanical power, how generators produce electrical energy, and how transformers work.

1. About this chapter

This chapter explores magnetic fields, solenoids, electromagnetism, and devices like electric motors and generators.

2. Magnetic Field and Electromagnetism

Magnetic Field: Space around a magnet where magnetic force is experienced.
Oersted's Experiment: Current in a wire produces a magnetic field around it, deflecting a nearby compass needle.
Solenoid: Cylindrical coil of wire that creates a strong magnetic field inside.

3. Fleming's Rules and Motors

Fleming's Left-Hand Rule (LHR): Determines force direction on a conductor (Thumb = Force/Motion, Index = Magnetic Field, Middle = Current). Used in Electric Motors.
Electric Motor: Device converting electrical energy to mechanical energy using magnetic torque.

4. Electromagnetic Induction and Generators

Electromagnetic Induction: A changing magnetic field produces an induced EMF in a coil (Faraday's discovery).
Fleming's Right-Hand Rule (RHR): Determines direction of induced current.
Electric Generator: Converts mechanical energy to electrical energy using slip rings (AC) or split rings (DC).

Key formulas & results

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

Magnetic Force on a Current-Carrying Conductor

F = B I L sin(theta)

B = magnetic field, I = current, L = length of conductor, theta = angle.

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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

✗ Confusing Fleming's Left-Hand and Right-Hand Rules.

✓ Use the Left-Hand rule for motors (force direction when current is applied) and the Right-Hand rule for generators/induced current.

WATCH OUT

✗ Thinking magnetic lines of force cross each other.

✓ Magnetic lines of force never intersect; if they did, the compass would point in two directions at once.

NCERT exercises (with solutions)

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

Multiple Choice Questions

Questions on solenoid, magnetic field lines, and electromagnetic induction.

Questions

Short Answer Questions

Fleming's rules, solenoid fields, and AC vs DC generator differences.

Questions

Practice problems

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

Q1EASY· Concept

What is electromagnetic induction?

▶ Show solution

The phenomenon of producing an induced electromotive force (EMF) and current in a circuit due to a change in the magnetic flux linked with it.

Q2MEDIUM· Concept

Differentiate AC and DC generators.

▶ Show solution

1. AC generator produces alternating current (changes direction periodically) and uses slip rings. 2. DC generator produces direct current (flows in a single direction) and uses split ring commutators.

5-minute revision

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

•Magnetic lines flow North to South outside a magnet.
•Current-carrying wire produces a magnetic field.
•Fleming's LHR: Motor force (Thumb=Force, Index=Field, Middle=Current).
•Fleming's RHR: Generator (Thumb=Motion, Index=Field, Middle=Induced Current).

Tamil Nadu (TNBSE) marks blueprint

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

Typical chapter weightage: 5-6 marks in assessments

Question type	Marks each	Typical count	What it tests
MCQ	1	1-2	Base concepts and definitions
Short Answer	2-3	1-2	Descriptive and application points

Prep strategy

Understand core definitions and solve standard textbook problems.
Review common mistakes to avoid losing easy marks.

Where this shows up in the real world

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

Electric Motors

Found in fans, washing machines, pumps, and electric cars to convert electrical energy to mechanical work.

Power Generators

Dams, wind turbines, and coal plants use large generators based on electromagnetic induction to produce electricity.

Exam strategy

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

Write definitions precisely as defined in the textbook.
Draw neat, labeled diagrams for biology and physics chapters.

Going beyond the textbook

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

Read advanced reference materials to explore concepts beyond the school syllabus.

Where else this chapter is tested

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

Class 9 Annual ExamsHigh

NTSE Stage 1Medium

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Questions students ask

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

A coil of many circular turns of insulated copper wire wrapped closely in the shape of a cylinder. It behaves like a bar magnet when current flows through it.

1. Increase the current. 2. Increase the number of turns in the coil. 3. Use a soft iron core.

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