Class 10 Science Chapter 12 — Magnetic Effects of Electric Current (International Edition)

NCERT / RBSE Syllabus 2026–27 · Learn by doing · Includes four labelled diagrams

Prepared by: NCERTClasses Team — textbook specialists and experienced teachers.
Based on: NCERT Class 10 Science textbook, Chapter 12, and the Board of Secondary Education, Rajasthan syllabus 2026–27.
Published: 24 September 2026 · Last updated: 24 September 2026

In 1820, Hans Christian Ørsted was teaching a class when he noticed something by chance — the moment current flowed through a nearby wire, a compass needle sitting some distance away swung sharply. Electricity and magnetism, treated as entirely separate subjects for centuries, had just turned out to be connected.

That single discovery is exactly what powers every electric motor, fan, and household fuse today.

How to read this — first you think or try it, then comes the explanation:
🔍 Wonder · 🧪 Try it · 📖 Understand · 🔗 Apply · ✅ Check yourself
"Check yourself" has three levels — 1, 2, 3.

Contents

1. Foundation check
2. Magnetic field and field lines
3. Field due to a straight conductor
4. Field due to a circular loop
5. Solenoid and electromagnet
6. Force on a conductor — Fleming's left-hand rule
7. Domestic electric circuits
8. Your ladder
9. Marking scheme
10. Common mistakes
11. Final test
12. Glossary
13. For parents and teachers
14. Beyond NCERT

Foundation check

1. How many poles does a magnet have?
2. What happens when like poles are brought close together?
3. What is Ohm's law's formula? (Chapter 11)

Answers

1. Two — north and south. 2. Repulsion (they push apart). 3. V=IR. This chapter examines why that same current, flowing through a wire, starts behaving like a magnet in its own right.

1. Magnetic field and field lines

🔍 Wonder — Why does a compass needle always settle in a north-south direction?

🧪 Try it — Place a bar magnet under a sheet of paper, sprinkle iron filings on top, and tap gently. Think first — will the filings scatter randomly, or form a pattern?

What happened? The filings arranged themselves into curved lines — dense near the poles, sparse farther away. This is how magnetic field lines are made visible.

📖 Understand — The region around a magnet where its influence can be felt is called the magnetic field, measured in tesla (T). It is represented using field lines:

• Outside the magnet, lines emerge from the north pole and merge into the south pole (inside the magnet they run south to north, forming closed loops).
• Two field lines never cross — if they did, a compass needle placed at that point would have to point in two directions at once, which is impossible.
• Where lines are denser, the field is stronger.

Figure 1 — A bar magnet's field lines run from the north pole to the south pole outside, and south to north inside — forming a closed loop.

🔗 Apply — Earth itself behaves like a giant magnet, which is exactly why a freely suspended compass always settles roughly north-south.

✅ Check yourself

Level 1 Which pole do field lines emerge from? — Answer: The north pole.
Level 2 Why do two field lines never cross? — Answer: At the crossing point, a compass needle would have to point in two different directions at once, which is impossible.

2. Field due to a straight conductor

🔍 Wonder — In Ørsted's experiment, why did the compass needle move the moment current flowed, when there was no magnet anywhere near the wire?

Figure 2 — Field lines around a straight wire form concentric circles; the right-hand thumb rule gives their direction.

📖 Understand — Any current-carrying conductor generates a magnetic field around itself — this was Ørsted's discovery. Around a straight wire, this field forms concentric circles, denser closer to the wire.

To find the direction, use the right-hand thumb rule (Maxwell's rule) — grip the conductor with your right hand so that your thumb points in the direction of current; your curled fingers then show the direction of the magnetic field lines.

Worked example 1: A straight wire lies north-south, carrying current from north to south. Which way will a compass needle placed directly above the wire turn?
Solution: Apply the right-hand thumb rule — point the thumb in the current's direction (north to south). Directly above the wire, the curled fingers point toward the west. So the compass needle's north end will swing west — exactly the kind of result Ørsted originally observed.

🔗 Apply — Field strength increases with higher current and decreases with distance from the wire.

✅ Check yourself

Level 1 What shape do field lines take around a straight wire? — Answer: Concentric circles.
Level 2 What does the thumb represent in the right-hand thumb rule? — Answer: The direction of current.
Level 3 If the current's direction is reversed, what happens to the field's direction? — Answer: It reverses too — reapplying the right-hand rule, the curled fingers now point exactly opposite to before.

3. Field due to a circular loop

🔍 Wonder — If a straight wire is bent into a loop, how does the field pattern change?

📖 Understand — At every point along a circular loop, concentric circles still form (just as with a straight wire), but near the centre of the loop, these circles become so large that they appear as nearly straight, parallel lines. More turns in the loop mean a stronger field — each turn adds its own contribution.

🔗 Apply — This is exactly the foundation for the solenoid (next section) — wrapping many loops one after another multiplies the field many times over.

✅ Check yourself

Level 1 What do field lines look like at the centre of a circular loop? — Answer: Nearly straight, parallel lines.
Level 2 How does increasing the number of turns affect the field? — Answer: It strengthens the field — each turn adds its own contribution.

4. Solenoid and electromagnet

Figure 3 — A solenoid's field is exactly like a bar magnet — one end behaves as a north pole, the other as a south pole, with a uniform field inside.

📖 Understand — Many turns of wire wound closely in a cylindrical shape form a solenoid. When current flows through it, the magnetic field produced is exactly like that of a bar magnet — one end behaves like a north pole, the other like a south pole. Inside, the field lines are straight and parallel — the field is uniform.

Electromagnet — placing a soft iron core inside a solenoid greatly strengthens the magnetic field — this is an electromagnet. Its key trait: it behaves as a magnet only as long as current flows — switch the current off, and the magnetism nearly vanishes.

🔗 Apply — This exact trait makes electromagnets far more useful than permanent magnets in many settings — cranes that lift and drop heavy iron scrap, or electric bells, simply switch the current on or off to control the magnetism at will.

✅ Check yourself

Level 1 What is the field like inside a solenoid? — Answer: Uniform (straight, parallel lines).
Level 2 Why is a soft iron core placed inside an electromagnet? — Answer: To greatly strengthen the magnetic field.
Level 3 Why are electromagnets, not permanent magnets, used in cranes that lift scrap iron? — Answer: An electromagnet's magnetism is controlled by current — switching current on lifts the heavy iron, switching it off releases it instantly. A permanent magnet offers no such control.

5. Force on a conductor — Fleming's left-hand rule

🔍 Wonder — We've seen that current creates a magnetic field. Does the reverse also happen — can a magnetic field push on a current-carrying wire?

Figure 4 — Fleming's left-hand rule: forefinger for field, middle finger for current, thumb for force — all three mutually perpendicular.

📖 Understand — Yes! When a current-carrying conductor is placed in a magnetic field, it experiences a mechanical force — this is the working principle of the electric motor. To find this force's direction, use Fleming's left-hand rule:

Stretch the forefinger, middle finger and thumb of the left hand mutually perpendicular

Memory aid: FBI — Fore-finger = Field, seCond finger = Current, thUmb = Force.

Worked example 2: A conductor carries current from north to south, and the magnetic field points from west to east. Find the direction of the force on the conductor.
Solution: Point the left hand's forefinger in the field's direction (west to east) and the middle finger in the current's direction (north to south) — holding all three mutually perpendicular, the thumb points vertically upward. So the force on the conductor acts upward.

Electric bell — another everyday application of the electromagnet: pressing the button magnetises a solenoid, which pulls a hammer toward it; the hammer strikes the bell, which breaks the contact in the process; the magnetism vanishes, the hammer springs back — and this cycle repeats rapidly for as long as the button stays pressed.

🔗 Apply — The force is always perpendicular to both current and field — which is exactly why, when this force is continually redirected the right way inside a motor, the coil keeps spinning continuously. This is the core principle behind every electric motor, from ceiling fans to mixers.

✅ Check yourself

Level 1 What does the thumb represent in Fleming's left-hand rule? — Answer: The direction of force (motion).
Level 2 Which device's principle is this rule the basis of? — Answer: The electric motor.
Level 3 If the current's direction is reversed but the field stays the same, what happens to the force's direction? — Answer: It reverses too — which is exactly why a motor's coil current is switched every half-turn (via a split-ring arrangement), so the force always acts in the direction that keeps it turning.

6. Domestic electric circuits

📖 Understand — In India, household supply is typically 220 V, delivered through three wires:

Why is the earth wire necessary? If a fault causes current to leak into an appliance's outer metal casing, the earth wire safely conducts it into the ground — so anyone touching the appliance doesn't receive a shock. (The fuse/MCB from Chapter 11's short-circuit and overloading protection is also part of this same domestic circuit.)

🔗 Apply — All household appliances are connected in parallel (recall Chapter 11) so every appliance gets the full 220 V, and switching one off doesn't affect the rest.

✅ Check yourself

Level 1 What colour is the earth wire typically? — Answer: Green.
Level 2 What is the earth wire's main job? — Answer: To safely conduct any current leaking into an appliance's metal casing into the ground, preventing electric shock.

Your ladder

Marking scheme

(An example of a typical examiner's approach — not an official scheme.)

Question (5 marks): Why is a solenoid's magnetic field like that of a bar magnet? Explain with a labelled diagram, and state one difference between an electromagnet and a permanent magnet.

Definition of a solenoid. 1 mark
Labelled diagram — field lines, poles. 2 marks
Reason for the bar-magnet comparison. 1 mark
One difference between electromagnet and permanent magnet. 1 mark

Common mistakes

Final test — mixed

9+ correct = chapter mastered.

1. Which pole do magnetic field lines emerge from?
2. Why do two field lines never cross?
3. What shape do field lines take around a straight wire?
4. What does the thumb represent in the right-hand thumb rule?
5. What is the field like inside a solenoid?
6. Why is a soft iron core placed in an electromagnet?
7. What does the thumb represent in Fleming's left-hand rule?
8. Which device's principle is this rule the basis of?
9. What colour is a home's earth wire typically?
10. (Chapter 11) What is always true of equivalent resistance in parallel?
11. (Chapter 10) Which lens corrects myopia?

Answers — 1. North pole | 2. A single point can't show two directions | 3. Concentric circles | 4. Direction of current | 5. Uniform (straight, parallel lines) | 6. To greatly strengthen the field | 7. Force/motion direction | 8. Electric motor | 9. Green | 10. Always less than the smallest individual resistor | 11. Concave lens

Glossary

For parents and teachers

Five-minute check: Have them demonstrate both hand-rules — which finds field, which finds force. Why does a solenoid resemble a bar magnet? Why is a home's earth wire necessary?

To try at home: a bar magnet + paper + iron filings — a completely safe way to actually "see" field lines for themselves.

Beyond NCERT — For Curious Readers

This section goes beyond the RBSE/NCERT Class 10 syllabus and is not required for the board exam. It draws only on government and internationally reputed university sources, for curious readers who want to see where this chapter leads.

Ørsted's discovery was, by most historical accounts, a genuine accident

Hans Christian Ørsted's 1820 discovery reportedly happened during a lecture demonstration — he was showing current heating a wire when he noticed a nearby compass needle deflect. Historians of science regard it as one of the rare major discoveries that emerged not from a deliberately designed experiment, but from one alert scientist noticing something unplanned. This single observation opened up the entire field now known as electromagnetism — the unified study of electric and magnetic phenomena.

Faraday found the exact reverse relationship

This chapter shows that current produces a magnetic field. A few years later, English scientist Michael Faraday demonstrated the converse — that a changing magnetic field can itself induce a current in a wire. This principle, electromagnetic induction, is the foundation of every electric generator in use today — precisely how power stations turn turbine motion into the electricity supplied to homes. This chapter's content and generator theory covered in later years of schooling are two sides of the very same coin.

Maglev trains

Trains such as those operating in Japan and China use powerful electromagnets to levitate above the track without touching it, and to propel themselves forward — an advanced, large-scale application of exactly this chapter's "force on a current-carrying conductor" principle. With friction against the track reduced to almost zero, these trains can exceed 500 km/h.

MRI machines — a giant electromagnet in medicine

At the heart of the MRI (Magnetic Resonance Imaging) machines used in hospitals sits an extremely powerful electromagnet — typically thousands of times stronger than Earth's own magnetic field. It helps produce detailed images of internal body tissue without any harmful radiation — a life-saving medical application built on the same core principle this chapter introduces.

How the ammeter works

Chapter 11 introduced the ammeter simply as "a device that measures current." In reality, a traditional pointer-style ammeter contains a small coil suspended within a permanent magnet's field — the moment current flows, exactly this chapter's "force on a conductor" principle pushes on the coil, rotating it by an amount proportional to the current. That rotation moves the pointer, giving the reading. This underlying device, called a galvanometer, is the basis for both ammeters and voltmeters — a direct, practical application of this very chapter.

India's electric motor manufacturing industry

Under India's Ministry of Heavy Industries, the country has a substantial domestic industry manufacturing electric motors, fans and generators — every fan, mixer, and pump running in a home works on exactly Fleming's left-hand rule, covered in this chapter.

Sources for this section

• ncert.nic.in — NCERT, Government of India
• ePathshala — Ministry of Education, Government of India
• mohfw.gov.in — Ministry of Health and Family Welfare, Government of India (for the MRI reference)

Note: nothing from these sources has been copied into this text; all statements above are written in the author's own words for general educational understanding, and are not medical or engineering advice.

Continue reading
← Previous: Chapter 11 — Electricity (7 marks)
→ Next: Chapter 13 — Our Environment (5 marks)

Related material

• Chapter 11 — Electricity (English)
• Chapter 10 — The Human Eye and the Colourful World (English)
• Class 10 Science Mega Test — 200 MCQs

Based on the Class 10 Science (Code 07) syllabus 2026–2027 of the Board of Secondary Education, Rajasthan, Ajmer — Chapter 12, marks weightage 6. Textbook: Science, NCERT. All diagrams are original.