A magnetic field is a region around a magnet where magnetic force is experienced. Magnetic field lines: imaginary lines showing the direction and strength of the magnetic field. Properties: (1) They form closed loops from N to S outside the magnet, and S to N inside. (2) They never intersect. (3) Closer field lines indicate stronger field. (4) Direction: North pole to South pole outside the magnet. A compass needle aligns itself with the magnetic field. Earth has a magnetic field — geographic North pole is near magnetic South pole.

Oersted (1820): discovered that a current-carrying conductor produces a magnetic field around it. A compass needle placed near a current-carrying wire gets deflected — proving current produces magnetism. Magnetic field around a straight wire: circular field lines; direction given by Right-Hand Thumb Rule — thumb points in direction of current, curled fingers show field direction. Solenoid: a coil of insulated copper wire — produces a uniform magnetic field inside similar to a bar magnet. Electromagnet: solenoid with a soft iron core — strong magnetic field only when current flows; used in electric bells, cranes, MRI machines. Strength increases with: more turns, more current, soft iron core.

A current-carrying conductor in a magnetic field experiences a force (Fleming's Left Hand Rule — FBI rule): Hold left hand with forefinger (B — field direction), middle finger (I — current direction), and thumb (F — force/motion direction) all mutually perpendicular. Electric motor: converts electrical energy to mechanical energy. Principle: current-carrying coil in a magnetic field rotates due to the force. Components: armature coil, permanent magnet, split ring commutator (reverses current direction every half turn to maintain rotation), brushes. Used in: fans, mixers, electric vehicles, washing machines.

Faraday's Law: A changing magnetic field (or movement of a conductor in a magnetic field) induces an EMF (electromagnetic induction). Fleming's Right Hand Rule: for induced current direction — forefinger (field), thumb (motion), middle finger (induced current). Electric generator: converts mechanical energy to electrical energy. AC generator: produces alternating current (changes direction periodically); uses slip rings. DC generator: produces direct current; uses split ring commutator. In India: AC supply at 220V, 50 Hz. Induced current direction: given by Lenz's Law — induced current opposes the change causing it (conservation of energy).

Domestic wiring uses three wires: Live (L) — red/brown, high potential; Neutral (N) — black/blue, zero potential; Earth (E) — green/yellow, safety wire connected to ground. A fuse (or MCB) is connected in the live wire. Earth wire protects against electric shock — if current leaks to appliance body, it flows to earth instead of through person. Short circuit: live and neutral wires touch — very high current → fuse melts/MCB trips. Overloading: connecting too many appliances → excess current → fire hazard. Each circuit in a house has its own fuse. Earthing is essential for appliances with metal bodies. Miniature Circuit Breakers (MCBs) are safer and reusable alternatives to fuses.