NCERT Solutions for Class 10 Science Chapter 12: Magnetic Effects of Electric Current

These Class 10 Science Chapter 12 solutions cover Magnetic Effects of Electric Current from the NCERT textbook (session 2026–27). You will find every in-text “Questions” box and the complete end-of-chapter Exercises reproduced exactly as in the book, followed by clear, exam-ready answers — including the right-hand thumb rule, Fleming’s left-hand rule, magnetic field lines, electromagnets and domestic electric circuits.

Class: 10 Subject: Science Chapter: 12 Topic: Magnetic Effects of Electric Current Branch: Physics Session: 2026–27
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Class 10 Science Chapter 12 Solutions – Overview

Chapter 12, Magnetic Effects of Electric Current, builds on the heating effect studied in “Electricity” and shows that electricity and magnetism are deeply linked — a fact Hans Christian Oersted discovered in 1820 when a compass needle was deflected by a nearby current-carrying wire. The chapter explains the magnetic field and its field lines, the pattern of the field around a straight conductor, a circular loop and a solenoid, and how a solenoid’s strong uniform field makes an electromagnet. It then studies the force on a current-carrying conductor placed in a magnetic field (the basis of the electric motor), introduces Fleming’s left-hand rule, and finishes with domestic electric circuits — live, neutral and earth wires, fuses, overloading and short-circuiting.

Key Concepts & Rules

Magnetic field: the region around a magnet (or a current-carrying conductor) where its force can be detected. It is a vector — it has both magnitude and direction.

Magnetic field lines: closed curves that emerge from the north pole and merge at the south pole outside the magnet (and run south → north inside it). They never cross; closer lines mean a stronger field.

Field of a straight wire: concentric circles around the wire; the field increases with current and decreases with distance.

Solenoid: a closely wound cylindrical coil; its field is uniform and like a bar magnet’s, with each end acting as a pole. A soft-iron core inside gives an electromagnet.

Force on a conductor: a current-carrying conductor in a magnetic field experiences a force, greatest when current and field are at right angles.

Right-hand thumb rule: hold the wire in the right hand with the thumb along the current; the curled fingers give the direction of the magnetic field lines.

Fleming’s left-hand rule: stretch the thumb, forefinger and middle finger of the left hand mutually perpendicular — Forefinger = magnetic Field, Centre finger = Current, Thumb = Thrust (force/motion).

Domestic supply (India): AC, 220 V, 50 Hz. Live wire = red, neutral = black, earth = green.

In-text “Questions” — Answers

Page 197

1. Why does a compass needle get deflected when brought near a bar magnet?

ANSWER A compass needle is itself a tiny bar magnet that is free to rotate. When it is brought near a bar magnet, it enters the magnet’s magnetic field. The poles of the needle experience magnetic forces — like poles repel and unlike poles attract. These forces turn the needle until it aligns along the direction of the magnetic field, so the needle is deflected from its earlier position.

Page 200

1. Draw magnetic field lines around a bar magnet.

ANSWER The field lines are closed curves. Outside the magnet they come out of the north pole, curve around the sides, and go into the south pole; inside the magnet they run from the south pole to the north pole, so each line forms a complete loop. The lines are most crowded near the two poles (where the field is strongest) and more widely spaced in the middle. Arrows on each line point from N to S outside the magnet, and no two lines cross.

2. List the properties of magnetic field lines.

ANSWER (i) They are closed, continuous curves — emerging from the north pole and merging into the south pole outside the magnet, and running S to N inside it. (ii) They show the direction of the field — the direction in which a free north pole (the north end of a compass) would move at that point. (iii) They are crowded where the field is strong and spread out where it is weak. (iv) No two field lines ever intersect each other.

3. Why don’t two magnetic field lines intersect each other?

ANSWER The field has only one direction at any given point. If two field lines crossed, then at the point of intersection the compass needle would have to point in two different directions at the same time, which is impossible. Hence field lines never intersect.

Page 201–202

1. Consider a circular loop of wire lying in the plane of the table. Let the current pass through the loop clockwise. Apply the right-hand rule to find out the direction of the magnetic field inside and outside the loop.

ANSWER Applying the right-hand thumb rule to small sections of the loop, every part of the wire produces a field in the same direction at the centre. For a current flowing clockwise (as seen from above), the magnetic field inside the loop is directed into the plane of the table (downwards, away from the viewer). Outside the loop the field is in the opposite sense, i.e. it is directed out of the plane of the table (upwards).

2. The magnetic field in a given region is uniform. Draw a diagram to represent it.

ANSWER A uniform magnetic field is represented by equally spaced, parallel straight lines all pointing in the same direction (for example, equal horizontal arrows pointing left to right). Equal spacing shows that the field has the same magnitude everywhere, and the parallel arrows show it has the same direction everywhere.

3. Choose the correct option.The magnetic field inside a long straight solenoid-carrying current(a) is zero.   (b) decreases as we move towards its end.   (c) increases as we move towards its end.   (d) is the same at all points.

ANSWER (d) is the same at all points. Inside a long current-carrying solenoid the field lines are parallel straight lines, so the field is uniform — equal in magnitude and direction at every interior point.

Page 203–204

1. Which of the following property of a proton can change while it moves freely in a magnetic field? (There may be more than one correct answer.)(a) mass   (b) speed   (c) velocity   (d) momentum

ANSWER (c) velocity and (d) momentum. The magnetic force on a moving charge always acts perpendicular to its velocity, so it changes the direction of motion but not the speed. Since velocity (a vector) and momentum (mass × velocity) both depend on direction, they change. The proton’s mass and speed remain unchanged.

2. In Activity 12.7, how do we think the displacement of rod AB will be affected if (i) current in rod AB is increased; (ii) a stronger horse-shoe magnet is used; and (iii) length of the rod AB is increased?

ANSWER The force on a current-carrying conductor in a magnetic field increases with the current, with the strength of the field, and with the length of the conductor in the field. So in each case the force grows and the rod is displaced more: (i) If the current is increased, the force increases, so the displacement increases. (ii) If a stronger horse-shoe magnet is used (stronger field), the force increases, so the displacement increases. (iii) If the length of rod AB is increased, the force increases, so the displacement increases.

3. A positively-charged particle (alpha-particle) projected towards west is deflected towards north by a magnetic field. The direction of magnetic field is(a) towards south   (b) towards east   (c) downward   (d) upward

ANSWER (d) upward. Apply Fleming’s left-hand rule: the middle finger (current) points west (direction of conventional current for a positive charge moving west), and the thumb (force) points north (the deflection). The forefinger then points upward, which is the direction of the magnetic field.

Page 205

1. Name two safety measures commonly used in electric circuits and appliances.

ANSWER (i) Electric fuse: a thin wire of low melting point connected in the live wire; it melts and breaks the circuit if the current rises dangerously (overloading or short circuit), protecting the wiring and appliances. (ii) Earthing (earth wire): the metallic body of an appliance is connected to a green earth wire joined to a metal plate deep in the ground. This provides a low-resistance path so that any leakage current flows to earth, preventing severe electric shock.

2. An electric oven of 2 kW power rating is operated in a domestic electric circuit (220 V) that has a current rating of 5 A. What result do you expect? Explain.

ANSWER Current drawn by the oven, I = P / V. I = 2000 W ÷ 220 V = 9.09 A (approximately). This current (about 9.09 A) is much larger than the circuit’s rating of 5 A. The circuit will be overloaded; the excessive current produces heavy Joule heating, so the fuse will melt (or the wiring may overheat) and the circuit will break. Hence the oven should not be run on a 5 A circuit.

3. What precaution should be taken to avoid the overloading of domestic electric circuits?

ANSWER (i) Do not connect too many high-power appliances to a single socket or circuit at the same time. (ii) Use a fuse of suitable rating and good-quality wires of adequate thickness. (iii) Avoid joining the live and neutral wires (prevent short circuits) by using properly insulated, undamaged wiring. (iv) Use a stabiliser where supply voltage fluctuates, and run high-rating appliances such as geysers and air-coolers on a separate 15 A circuit.

End-of-chapter Exercises — Solutions

1. Which of the following correctly describes the magnetic field near a long straight wire?(a) The field consists of straight lines perpendicular to the wire.(b) The field consists of straight lines parallel to the wire.(c) The field consists of radial lines originating from the wire.(d) The field consists of concentric circles centred on the wire.

ANSWER (d) The field consists of concentric circles centred on the wire. The magnetic field around a long straight current-carrying wire is made of concentric circles in planes perpendicular to the wire, as confirmed by the iron-filings pattern and the right-hand thumb rule.

2. At the time of short circuit, the current in the circuit(a) reduces substantially.(b) does not change.(c) increases heavily.(d) vary continuously.

ANSWER (c) increases heavily. In a short circuit the live and neutral wires touch directly, so the resistance of the path becomes very small. By I = V / R, a very small R gives a very large current, so the current increases heavily.

3. State whether the following statements are true or false.(a) The field at the centre of a long circular coil carrying current will be parallel straight lines.(b) A wire with a green insulation is usually the live wire of an electric supply.

ANSWER (a) True. Near the centre of a long circular coil (solenoid) the arcs of the field circles appear as parallel straight lines, giving a uniform field. (b) False. Green insulation is used for the earth wire, not the live wire. The live wire usually has red insulation.

4. List two methods of producing magnetic fields.

ANSWER (i) By using a permanent magnet, such as a bar magnet or a horse-shoe magnet, which has a magnetic field around it. (ii) By passing an electric current through a conductor — a straight wire, a circular coil or a solenoid — which produces a magnetic field around it (an electromagnet).

5. When is the force experienced by a current–carrying conductor placed in a magnetic field largest?

ANSWER The force is largest when the conductor is placed perpendicular (at right angles, 90°) to the direction of the magnetic field. When the current and the field are mutually perpendicular, the displacement (and hence the force) on the conductor is maximum.

6. Imagine that you are sitting in a chamber with your back to one wall. An electron beam, moving horizontally from back wall towards the front wall, is deflected by a strong magnetic field to your right side. What is the direction of magnetic field?

ANSWER The electrons move from the back wall to the front wall, so the conventional current is directed from front to back (opposite to electron motion). The force (deflection) is towards your right side. Applying Fleming’s left-hand rule with the thumb pointing right (force) and the middle finger pointing from front to back (current), the forefinger points downward. Hence the magnetic field is directed vertically downward.

7. State the rule to determine the direction of a (i) magnetic field produced around a straight conductor-carrying current, (ii) force experienced by a current-carrying straight conductor placed in a magnetic field which is perpendicular to it, and (iii) current induced in a coil due to its rotation in a magnetic field.

ANSWER (i) Right-hand thumb rule (also called Maxwell’s corkscrew rule): hold the wire in the right hand with the thumb along the current; the curled fingers give the direction of the field lines. (ii) Fleming’s left-hand rule: forefinger → field, middle finger → current, thumb → force/motion of the conductor. (iii) Fleming’s right-hand rule: forefinger → field, thumb → motion of the conductor, middle finger → direction of the induced current.

8. When does an electric short circuit occur?

ANSWER A short circuit occurs when the live wire and the neutral wire come into direct contact. This usually happens when the insulation of the wires is damaged or there is a fault in an appliance. The resistance of the path falls suddenly, the current rises abruptly to a very large value, and excessive Joule heating can cause fire or damage — which is why a fuse is used.

9. What is the function of an earth wire? Why is it necessary to earth metallic appliances?

ANSWER The earth wire (green insulation) is connected to a metal plate buried deep in the earth and provides a low-resistance conducting path to the ground. It is necessary to earth metallic appliances (such as electric press, toaster, refrigerator, table fan) because if the live wire accidentally touches the metallic body, the leakage current flows safely to the earth instead of through the user. This keeps the body of the appliance at the potential of the earth, so a person touching it does not receive a severe electric shock.

Extra Practice Questions

Short Answer Type Questions

Q1. Who discovered the magnetic effect of electric current, and how?

ANSWERHans Christian Oersted discovered it in 1820 when he noticed that a compass needle was deflected whenever an electric current passed through a metallic wire placed near it, showing that electricity and magnetism are related.

Q2. What is a solenoid, and why is its field useful?

ANSWERA solenoid is a coil of many circular turns of insulated copper wire wound closely in the form of a cylinder. Its field inside is strong and uniform, like a bar magnet’s, so it can magnetise a soft-iron core to make a powerful electromagnet.

Q3. Differentiate between an electromagnet and a permanent magnet.

ANSWERAn electromagnet (a solenoid with a soft-iron core) is magnetic only while current flows and its strength can be changed; a permanent magnet keeps its magnetism without any current and its strength is fixed.

Q4. State two ways to increase the strength of an electromagnet.

ANSWER(i) Increase the current through the coil, and (ii) increase the number of turns in the coil. Using a soft-iron core also greatly increases the field.

Q5. Why are the field lines inside a solenoid parallel and equally spaced?

ANSWERBecause the magnetic field inside a long solenoid is uniform — it has the same magnitude and direction at every interior point — the field lines are drawn as parallel, equally spaced straight lines.

Long Answer Type Questions

Q1. Explain Fleming’s left-hand rule and state where it is applied.

ANSWERFleming’s left-hand rule helps find the direction of the force on a current-carrying conductor placed in a magnetic field. Stretch the thumb, forefinger and middle finger of the left hand so that they are mutually perpendicular. If the forefinger points in the direction of the magnetic field and the middle finger in the direction of the current, then the thumb points in the direction of the force (motion) on the conductor. The force is greatest when the current and field are at right angles. This rule is the working principle of devices such as electric motors, loudspeakers, microphones and moving-coil measuring instruments.

Q2. Describe the structure of a common domestic electric circuit and the role of each wire.

ANSWERA home receives AC power at 220 V, 50 Hz through three wires. The live wire (red insulation) carries current at high potential; the neutral wire (black insulation) completes the circuit at near-zero potential; the potential difference between them is 220 V. The earth wire (green insulation) is connected to a metal plate in the ground for safety. The wires pass through an electricity meter and main fuse to the main switch, then to separate circuits — often a 15 A circuit for heavy appliances (geysers, coolers) and a 5 A circuit for bulbs and fans. Appliances are connected in parallel across live and neutral so each gets the full 220 V and has its own switch. A fuse in the live wire protects against overloading and short-circuiting.

Q3. How does the magnetic field around a straight conductor depend on current and distance? How is its direction found?

ANSWERThe magnetic field around a long straight current-carrying conductor forms concentric circles in planes perpendicular to the wire. Its magnitude is directly proportional to the current — increasing the current increases the field at a given point — and it decreases as the distance from the wire increases, which is why the iron-filing circles grow larger and fainter farther out. The direction of the field is found by the right-hand thumb rule: holding the wire in the right hand with the thumb pointing along the current, the curled fingers show the direction of the circular field lines. Reversing the current reverses the direction of the field.

MCQs & Assertion–Reason

1. The magnetic field around a long straight current-carrying wire is in the form of:

(a) radial lines    (b) parallel straight lines    (c) concentric circles    (d) ellipses

2. Who first observed the magnetic effect of electric current?

(a) Faraday    (b) Oersted    (c) Ampere    (d) Maxwell

3. The direction of magnetic field around a straight conductor is given by:

(a) Fleming’s left-hand rule    (b) Fleming’s right-hand rule    (c) right-hand thumb rule    (d) Lenz’s law

4. Inside a long current-carrying solenoid, the magnetic field is:

(a) zero    (b) uniform    (c) strongest at the centre only    (d) circular

5. Fleming’s left-hand rule gives the direction of:

(a) magnetic field    (b) current    (c) force on the conductor    (d) induced current

6. The potential difference between the live and neutral wires in Indian homes is:

(a) 110 V    (b) 220 V    (c) 12 V    (d) 440 V

7. The earth wire of a domestic circuit has insulation of colour:

(a) red    (b) black    (c) green    (d) blue

8. The force on a current-carrying conductor in a magnetic field is maximum when the angle between current and field is:

(a) 0°    (b) 45°    (c) 90°    (d) 180°

9. An electromagnet uses a core of:

(a) steel    (b) soft iron    (c) copper    (d) aluminium

10. At the time of a short circuit, the current in the circuit:

(a) decreases    (b) becomes zero    (c) increases heavily    (d) stays the same

Answer key: 1-(c), 2-(b), 3-(c), 4-(b), 5-(c), 6-(b), 7-(c), 8-(c), 9-(b), 10-(c).

For each Assertion–Reason question, choose: (A) Both true and the Reason correctly explains the Assertion; (B) Both true but the Reason is not the correct explanation; (C) Assertion true, Reason false; (D) Assertion false, Reason true.

A-R 1. Assertion: Two magnetic field lines never intersect each other.

Reason: At a point of intersection the compass needle would have to point in two directions at once, which is impossible.

A-R 2. Assertion: The magnetic field inside a long solenoid is uniform.

Reason: The field lines inside such a solenoid are parallel straight lines.

A-R 3. Assertion: A soft-iron core is used in an electromagnet rather than steel.

Reason: Soft iron loses its magnetism easily when the current is switched off.

A-R 4. Assertion: The earth wire is connected to the metallic body of an appliance.

Reason: The earth wire carries the normal working current of the appliance.

A-R 5. Assertion: The magnetic force on a freely moving proton changes its speed.

Reason: The magnetic force always acts perpendicular to the velocity of the charge.

Answer key: 1-(A), 2-(A), 3-(A), 4-(C), 5-(D).

Common Mistakes & Exam Tips

Watch out for these

  • Mixing up the two Fleming’s rules — use the left hand for the force on a current (motor), and the right hand for the induced current (generator).
  • Forgetting that conventional current is opposite to the direction of electron flow when solving beam/charge problems.
  • Saying field lines “start and stop” — they are always closed loops and never cross.
  • Calling the green wire “live” — green is the earth wire; live is red and neutral is black.
  • Writing that a short circuit reduces current — resistance drops, so the current rises sharply.

How to score full marks in this chapter

For any direction question, write down which finger/hand rule you are using before stating the answer. In domestic-circuit numericals, always compute I = P / V and compare it with the circuit rating to justify overloading. Remember the colour code (live = red, neutral = black, earth = green) and the supply values (220 V, 50 Hz, AC). When asked to draw fields, label the poles, put arrows on the lines, and keep them closer near the poles — examiners award marks for these details.

Frequently Asked Questions

What is Class 10 Science Chapter 12 about?

Chapter 12, Magnetic Effects of Electric Current, deals with magnetic fields and field lines, the field due to a straight wire, a circular loop and a solenoid, electromagnets, the force on a current-carrying conductor (Fleming’s left-hand rule), and domestic electric circuits with fuses and earthing.

What is the difference between Fleming’s left-hand and right-hand rules?

Fleming’s left-hand rule gives the direction of the force on a current-carrying conductor in a magnetic field (used in motors), while Fleming’s right-hand rule gives the direction of the current induced when a conductor moves in a magnetic field (used in generators).

Why is the earth wire important in domestic circuits?

The green earth wire connects the metallic body of an appliance to the ground through a low-resistance path. If the live wire touches the body, the leakage current flows safely to earth instead of through the user, preventing severe electric shock.

Are these Class 10 Science Chapter 12 solutions free?

Yes. All solutions are free and follow the official NCERT Science textbook for session 2026–27, with every in-text and exercise question solved step by step.

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