Where Mindful Learning Begins
Where Mindful Learning Begins
Class 10 Science NCERT Solutions Chapter 12 (CBSE 2026-27) — every in-text question, every embedded Activity question, and all 9 back-of-chapter Exercises on this one page, solved with full reasoning.
Magnetic Effects of Electric Current picks up right where Chapter 11 left off — a current-carrying wire, it turns out, behaves like a magnet. The chapter builds from magnetic field lines around a bar magnet, to the concentric-circle field around a straight current-carrying wire (found with the right-hand thumb rule), to the fields of a circular loop and a solenoid (which behaves just like a bar magnet, and is the basis of an electromagnet), to the force a magnetic field exerts on a current-carrying conductor (found with Fleming's left-hand rule) — and closes with domestic electric circuits: live, neutral and earth wires, short circuits, overloading, and fuses. These NCERT solutions work through every Activity-based conceptual question and the full 9-question Exercise set in detail.
Magnetic Effects of Electric Current is built entirely around one surprising fact, first observed by Hans Christian Oersted: a wire carrying current deflects a nearby compass needle, meaning current produces its own magnetic field. The chapter works out what that field looks like in three shapes — straight wire (concentric circles, found with the right-hand thumb rule), circular loop (field lines straighten out at the centre), and solenoid (a uniform field just like a bar magnet, which is what makes an electromagnet possible) — before turning the relationship around: if current creates a magnetic field, does a magnetic field exert a force on a current-carrying conductor placed inside it? It does, and Fleming's left-hand rule gives its direction, which is the working principle behind devices like electric motors. The chapter closes with something every household actually uses this physics for: domestic electric circuits — the live, neutral and earth wires, why appliances are wired in parallel, and how short circuits, overloading, and fuses actually work. Every question woven through the chapter is solved here, section by section, in the order the textbook presents it: all thirteen "QUESTIONS" spread across the chapter, the questions embedded directly inside the Activities, and the full 9-question Exercise set at the end.
Magnetic field lines around a bar magnet and a straight current-carrying wire, found with the right-hand thumb rule.
Circular loops, solenoids and electromagnets, and Fleming's left-hand rule for the force on a current in a magnetic field.
Live, neutral and earth wires, why circuits use parallel wiring, and how short circuits, overloading and fuses work.
A compass needle is itself a small bar magnet. When brought near another bar magnet, it experiences a force due to the magnetic field of that magnet — this force causes it to align itself along the direction of the magnetic field, i.e., it gets deflected from its original (north-south) orientation.
The field lines emerge from the north pole, curve around outside the magnet, and merge into the south pole; inside the magnet, they run from the south pole back to the north pole, forming continuous closed loops. The lines are closer together (denser) near the poles, where the field is strongest.
If two field lines crossed at a point, it would mean that a compass needle placed at that point would have to point in two different directions at once — which is not possible, since the magnetic field at any given point has only one definite direction. Hence, field lines never intersect.
Applying the right-hand thumb rule around the loop (curling fingers in the direction of the clockwise current, as seen from above): the magnetic field points into the table (downward) inside the loop, and comes back out of the table (upward) outside the loop, consistent with field lines forming closed curves.
A uniform magnetic field is represented by a set of parallel, equally-spaced straight lines, all pointing in the same direction — showing that the field has the same magnitude and direction at every point in that region.
Answer: (d) is the same at all points — the field lines inside a solenoid are parallel straight lines, showing the field is uniform throughout its interior.
Answer: (c) velocity and (d) momentum. The magnetic force on a moving charged particle acts perpendicular to its velocity, so it changes the direction of motion (velocity, and hence momentum) without doing work on the particle — so its speed (and mass) remain unchanged.
In all three cases, the displacement (force) would increase: (i) increasing the current increases the force on the conductor; (ii) a stronger magnet produces a stronger magnetic field, increasing the force; (iii) a longer rod (within the magnetic field) experiences a greater total force, since more of the current-carrying conductor is within the field.
Answer: (d) upward. Applying Fleming's left-hand rule with current (motion of positive charge) towards the west and force (deflection) towards the north, the magnetic field must point vertically upward.
(i) Electric fuse — stops the flow of unduly high current, protecting the circuit and appliances from damage. (ii) Earth wire — provides a low-resistance path to the ground for any leakage current from a metallic appliance body, preventing electric shocks.
Current drawn by the oven = P/V = 2000W/220V ≈ 9.09 A, which is greater than the circuit's 5A current rating. This would cause the current in the circuit to exceed its safe limit, which would melt/blow the fuse, breaking the circuit — the oven should therefore not be operated on this circuit, or the circuit's rating needs to be increased.
Avoid connecting too many high-power appliances to a single socket or circuit at the same time; use separate circuits for high-power appliances (like geysers, air coolers) and low-power ones (like bulbs, fans); use appliances of a power rating suited to the circuit's current rating; and use fuses of the correct rating for each circuit.
It indicates that the electric current flowing through the wire has produced a magnetic effect — i.e., electricity and magnetism are linked, and a current-carrying conductor generates its own magnetic field around it.
The magnet exerts a force on the iron filings in the region surrounding it, causing them to align along that force. This demonstrates the existence of a magnetic field around the magnet, and the pattern the filings form represents the magnetic field lines.
Yes — reversing the current direction reverses the direction of the magnetic field lines. The deflection of the compass needle increases as the current through the wire increases (a stronger field), and decreases as the compass is moved farther from the wire (the field weakens with distance).
A current-carrying conductor placed inside a magnetic field experiences a force (as first suggested by Ampere) — this force displaces the rod. The direction of this force reverses if either the current direction or the magnetic field direction is reversed, since the force depends on both.
Answer: (d) The field consists of concentric circles centred on the wire.
Answer: (c) increases heavily.
(a) True — at the centre of a large circular coil, the field lines effectively straighten out into parallel lines.
(b) False — a wire with green insulation is usually the earth wire, not the live wire (the live wire has red insulation).
(i) Using a permanent magnet (e.g., a bar magnet). (ii) Passing an electric current through a conductor (e.g., a straight wire, circular loop, or solenoid).
The force is largest when the direction of the current is at right angles (perpendicular) to the direction of the magnetic field.
Since electrons move from the back wall towards the front wall, the conventional current is in the opposite direction — from the front wall towards you (back wall). Applying Fleming's left-hand rule with current towards you and force/deflection to your right, the magnetic field must be directed vertically downward (from ceiling to floor).
(i) Right-hand thumb rule: hold the conductor in your right hand with the thumb pointing in the direction of current — your fingers curl around the conductor in the direction of the magnetic field lines.
(ii) Fleming's left-hand rule: stretch the thumb, forefinger and middle finger of the left hand mutually perpendicular — forefinger = direction of field, middle finger = direction of current, and the thumb then gives the direction of the force.
(iii) Fleming's right-hand rule: stretch the thumb, forefinger and middle finger of the right hand mutually perpendicular — forefinger = direction of field, thumb = direction of motion of the conductor, and the middle finger then gives the direction of the induced current.
A short circuit occurs when the live wire and the neutral wire come into direct contact with each other (e.g., due to damaged insulation or a fault in an appliance). This causes the resistance in the circuit to drop suddenly, and the current increases abruptly to a very high value.
The earth wire provides a low-resistance conducting path, connected to a metal plate buried deep in the earth, and is connected to the metallic body of an appliance. If any current leaks to the appliance's metal body due to a fault, the earth wire safely carries this current to the ground, keeping the body at earth (zero) potential.
It is necessary to earth metallic appliances (like electric irons, toasters, refrigerators) because, without earthing, a fault could make the appliance's metal body "live" — carrying current — posing a serious electric shock hazard to anyone who touches it.
Next up is Chapter 13 — Our Environment, the final chapter in the Class 10 Science NCERT Solutions series. Or explore the full chapter list, browse the Class 10 Science hub, or book a free demo class for personalised coaching.
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