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Class 10 Magnetic Effects of Electric Current notes: NCERT Science Chapter 12 revision

CMDLearn · 4 November 2026

These are short revision notes for Chapter 12 of the NCERT Class 10 Science textbook, "Magnetic Effects of Electric Current" (pages 195 to 207, Reprint 2026-27). The chapter starts from one observation, that a wire carrying a current turns a compass needle, and builds from it: field lines, the field around a wire, a loop and a solenoid, the force on a wire in a field, and the wiring in our homes. The notes end with the key words, the two hand rules side by side, the common mistakes and 8 quick questions of our own with worked answers.

Keep the textbook open next to these notes. The wording here is our own; the textbook is the authority.

How much it counts

CBSE's Class 10 Science curriculum for 2026-27 puts this chapter in Unit IV, Effects of Current, worth 13 of the 80 theory marks, shared with Electricity (curriculum, PDF page 4). For this chapter it lists the magnetic field and field lines, the field around a straight conductor, a coil and a solenoid, the force on a conductor carrying a current, the left-hand rule of Fleming, direct and alternating current, the frequency of AC, the advantage of AC over DC, and domestic electric circuits. It names the electric motor, electromagnetic induction and the electric generator as topics assessed only at school, not in the board paper (PDF page 6). This reprint of the chapter has no sections on those three. On AC, it only says that homes get AC at 220 V and 50 Hz (page 206). More on the units: CBSE Class 10 Science syllabus 2026-27.

The chapter on one page

1. Magnetic field and field lines (section 12.1, pages 195-197)

• In 1820 Hans Christian Oersted saw a compass needle swing when a current flowed in a nearby wire. That showed that electricity and magnetism are related (page 195).
• A compass needle is itself a small bar magnet. The end that points roughly north is its north pole; like poles repel and unlike poles attract (page 196).
• The magnetic field of a magnet is the region round it where its force can be detected. Iron filings sprinkled round a magnet line up along the field lines (page 196).
• Properties of field lines (page 197): - the direction of the field is the way a compass north pole would move, so outside the magnet the lines go from N to S, and inside it from S to N: they are closed curves; - where the lines are closer together, the field is stronger; - two field lines never cross: at a crossing point a compass would have to point two ways at once.
• A magnetic field has both a size and a direction (page 197).

2. The field of a current (section 12.2, pages 197-201)

• Straight wire (pages 198-199): the field lines are concentric circles centred on the wire. Reversing the current reverses the field. A larger current gives a stronger field at a point; at a greater distance from the wire the field is weaker.
• Right-hand thumb rule (page 200): hold the wire in your right hand with the thumb along the current; your curled fingers show the direction of the field lines. (The book also calls it Maxwell's corkscrew rule.)
• Circular loop (pages 200-201): near the wire the circles are small; at the centre of the loop the field lines are almost straight, and every part of the loop adds to the field in the same direction. A coil of n turns gives a field n times that of one turn, because the current goes the same way round in every turn.
• Solenoid (page 201): a long coil of insulated copper wire wound closely like a cylinder. Outside, its field looks like a bar magnet's, with one end acting as a north pole and the other as a south pole. Inside, the field lines are parallel straight lines: the field is uniform.
• Electromagnet (page 201): the strong field inside a solenoid can magnetise a piece of soft iron placed in it.

3. Force on a current-carrying conductor (section 12.3, pages 202-203)

• If a current makes a field that pushes on a magnet, the magnet pushes back on the current: André-Marie Ampère suggested an equal and opposite force (page 202).
• In the book's activity, a small aluminium rod between the poles of a horse-shoe magnet moves when a current flows through it. Reversing either the current or the field reverses the direction of the force (pages 202-203).
• The force is largest when the current is at right angles to the field (page 203).
• Fleming's left-hand rule (page 203): stretch the thumb, first finger and middle finger of the left hand at right angles to one another. First finger = field, middle (second) finger = current, thumb = force (the motion of the conductor).
• Devices that use this force include electric motors, generators, loudspeakers, microphones and measuring instruments (page 203).
• Magnetism in medicine (box, page 204): nerve currents make very weak magnetic fields, strongest in the heart and the brain; MRI uses the body's magnetic fields to make images.

4. Domestic electric circuits (section 12.4, pages 204-205)

• The mains supply has a live wire (red insulation) and a neutral wire (black insulation), with 220 V between them. The supply is AC at 50 Hz (pages 204, 206).
• At the meter board the wires go through a main fuse and the electricity meter, then a main switch to the house circuits (page 204).
• Houses often have a 15 A circuit for high-power appliances such as geysers and air coolers, and a 5 A circuit for bulbs and fans (page 204).
• The earth wire (green insulation) goes to a metal plate deep in the ground. It is joined to the metal body of appliances such as an iron, toaster, table fan or refrigerator, so a leaking current flows away through a low-resistance path and the user does not get a severe shock (page 204).
• Appliances are connected in parallel, each with its own switch, so each gets the same potential difference (page 205).
• Short circuit: the live and neutral wires touch directly (damaged insulation or a faulty appliance) and the current jumps. Overloading can also come from a sudden rise in supply voltage or too many appliances on one socket. The fuse melts by Joule heating and breaks the circuit (page 205).

Key words at a glance

• Magnetic field: the region round a magnet where its force can be detected.
• Field line: the path a free north pole would tend to follow.
• Solenoid: a long, closely wound cylindrical coil of insulated wire.
• Electromagnet: a soft-iron core magnetised by the field of a solenoid.
• Live, neutral, earth: red, black and green insulation.
• Short circuit: live and neutral touching, so the current rises sharply.
• Overloading: more current than the circuit is rated for.

The two hand rules side by side

A quick way to keep them apart: Fleming's left hand gives the Force.

Mistakes that cost marks

• Drawing field lines that stop or cross. They are closed curves and never cross.
• Using the wrong hand. Field round a wire: right hand. Force on a wire in a field: left hand.
• Mixing up the fingers. First finger, field; second finger, current; thumb, force.
• Mixing up the wire colours. Live is red, neutral black, earth green.
• Calling every blown fuse a short circuit. Overloading (too many appliances, a voltage rise) also blows it.

Quick check: 8 questions of our own

These are our own questions, written for these notes and checked against the textbook pages named; no practising teacher has reviewed them yet. Every number was re-computed by a script.

Question 1. A long straight wire stands upright, and the current in it flows upwards. (a) Looked at from above, do the field lines go clockwise or anticlockwise? (b) A small compass is placed on the ground just to the east of the wire. Which way does its north pole point, if the wire's field is much stronger there than the Earth's? (c) What happens to the compass if the current is switched to flow downwards?

Answer: (a) anticlockwise; (b) north; (c) it turns to point south. (a) With the right thumb pointing up along the current, the fingers curl anticlockwise when seen from above (page 200). (b) On an anticlockwise circle, the point due east of the centre is moving north, so the field there points north, and a compass north pole lines up with the field (page 197). (c) Reversing the current reverses the field (page 198), so the needle swings round to point south.

Question 2. A student's notebook says: "Magnetic field lines start at the north pole and end at the south pole, and the field is strongest halfway between the poles, where the lines are spread out." Correct both mistakes.

Answer: field lines do not start or end, and the field is strongest where the lines are crowded. Outside the magnet the lines run from N to S, and inside it from S to N, so each line is a closed curve with no start or end. The strength of the field is shown by how close the lines are; they crowd together near the poles, so the field is strongest there (page 197).

Question 3. A horizontal wire carries a current from north to south. The magnetic field round it is vertical and points upwards. In which direction is the force on the wire?

Answer: towards the west. Use Fleming's left-hand rule (page 203): first finger up (the field), second finger pointing south (the current). With those two at right angles, the thumb points west. (Check: if the current ran south to north instead, the force would point east, since reversing the current reverses the force, page 203.)

Question 4. A student makes an electromagnet by winding insulated copper wire round a soft iron nail and connecting it to a cell. (a) Why a soft iron nail, and not a piece of copper or wood? (b) Using the chapter, name two changes to the coil and its circuit that make the field inside it stronger.

Answer: (a) soft iron is a magnetic material, so the coil's field magnetises it; (b) more turns of wire, or more current. (a) The strong field inside a solenoid can magnetise a piece of magnetic material, such as soft iron, placed inside it (page 201); copper and wood are not magnetised this way. (b) A coil of n turns gives a field n times that of one turn (page 201), and the field at a point grows when the current grows (page 199).

Question 5. On a 15 A household circuit at 220 V, a 2,000 W geyser and a 1,000 W electric iron are working together. (a) What current does each draw, to two decimal places, and what is the total? (b) Someone then switches on a 1,500 W room heater on the same circuit. What is the new total, and what should happen?

Answer: (a) about 9.09 A and 4.55 A, total about 13.64 A; (b) about 20.45 A, more than 15 A, so the circuit is overloaded and the fuse should melt. (a) I = P ÷ V: 2,000 ÷ 220 ≈ 9.09 A and 1,000 ÷ 220 ≈ 4.55 A. Appliances on a circuit are in parallel, so their currents add (page 205): 3,000 ÷ 220 ≈ 13.64 A, below 15 A. (b) 4,500 ÷ 220 ≈ 20.45 A. Too many appliances on one circuit is overloading, and the fuse breaks the circuit by Joule heating (page 205).

Question 6. A house has a 5 A circuit and a 15 A circuit, both at 220 V. Which circuit should each of these use: (a) a 9 W LED bulb; (b) a 1,500 W immersion rod for heating water? Show the current each draws.

Answer: (a) the 5 A circuit; (b) the 15 A circuit. (a) 9 ÷ 220 ≈ 0.04 A, tiny, so it suits the 5 A circuit used for bulbs and fans. (b) 1,500 ÷ 220 ≈ 6.82 A, more than 5 A, so it needs the 15 A circuit meant for high-power appliances (page 204).

Question 7. A 2.2 kW air conditioner runs on 220 V. (a) What current does it draw? (b) Which fuse would you choose for its line: 5 A, 13 A or 30 A? Give a reason for each one you reject.

Answer: (a) 10 A; (b) 13 A. (a) I = P ÷ V = 2,200 ÷ 220 = 10 A. (b) A 5 A fuse would melt every time the air conditioner ran normally. A 30 A fuse would let three times the normal current through before melting, so a fault could damage the wiring first. 13 A is just above the normal 10 A, so it carries the working current and melts when the current rises sharply in a fault (the fuse's job, page 205).

Question 8. A compass is placed near a long straight wire. Put these three set-ups in order, from the largest deflection of the needle to the smallest: (A) 2 A in the wire, compass 6 cm away; (B) 4 A in the wire, compass 2 cm away; (C) 2 A in the wire, compass 2 cm away. Explain the order.

Answer: B, then C, then A. At a given point the field grows with the current, and for a given current it weakens with distance (page 199). B and C are at the same distance, and B has more current, so B > C. C and A carry the same current, and C is closer, so C > A.

Revise with questions

Test yourself next: Class 10 Magnetic Effects of Electric Current, 8 practice questions with answers. Free practice on this chapter, marked instantly in your browser: Class 10 Magnetic Effects of Electric Current questions. The chapter before this one: Class 10 Electricity notes and Electricity questions with answers. For timed practice, the free Class 10 revision papers include a Science paper laid out in 1, 2, 3 and 5-mark sections.

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Sources

All checked on 4 November 2026. NCERT page numbers are the printed page numbers of the textbook (printed page = PDF page + 194).

• NCERT, Science, Textbook for Class X, Chapter 12, "Magnetic Effects of Electric Current" (pages 195-207, Reprint 2026-27): section 12.1 (pages 196-197); 12.2, the straight wire, the right-hand thumb rule, the loop and the solenoid (pages 197-201); 12.3, the force and Fleming's left-hand rule (pages 202-203); 12.4, domestic circuits (pages 204-205); summary (page 206). ncert.nic.in/textbook/pdf/jesc112.pdf
• CBSE, Science curriculum, Class X, 2026-27: unit marks (PDF page 4) and Unit IV contents for this chapter (PDF page 6): cbseacademic.nic.in/web_material/CurriculumMain27/SecPart1/Science_SecP1_2026-27.pdf

The facts, section numbers and figure numbers are from the documents above. The wording of these notes, the table of the two hand rules, the list of mistakes and the 8 questions are our own.

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