Key Points

Hans Christian Oersted discovered that an electric current flowing through a conductor produces a magnetic field around it, establishing the link between electricity and magnetism.

A magnetic field is the region around a magnet where its force can be detected. It is represented by imaginary lines called magnetic field lines, which show the direction and strength of the field.

Magnetic field lines are closed curves. By convention, they emerge from the north pole and merge at the south pole outside the magnet, and move from south to north inside the magnet.

The density of field lines indicates the magnetic field's strength; closer lines mean a stronger field. Two magnetic field lines never intersect each other.

The magnetic field lines around a straight current-carrying conductor are concentric circles. The field strength is directly proportional to the current and inversely proportional to the distance from the wire.

This rule determines the direction of the magnetic field. If you hold a current-carrying wire in your right hand with the thumb pointing in the direction of the current, your fingers will curl in the direction of the magnetic field lines.

At the center of a current-carrying circular loop, the magnetic field lines are straight and perpendicular to the plane of the loop. The field strength is proportional to the current and the number of turns.

A solenoid is a coil with many circular turns of insulated wire. When current flows through it, it behaves like a bar magnet, with a strong and uniform magnetic field inside it.

An electromagnet is a temporary magnet created by placing a soft iron core inside a current-carrying solenoid. Its strength can be changed by varying the current or the number of turns.

A conductor carrying a current experiences a force when placed in a magnetic field. The force is maximum when the direction of the current is perpendicular to the direction of the magnetic field.

This rule finds the direction of the force on a conductor. If the forefinger points in the direction of the magnetic field and the middle finger in the direction of the current, the thumb indicates the direction of the force.

In domestic circuits, the live wire (red insulation) is at a high potential, the neutral wire (black insulation) is at zero potential, and the earth wire (green insulation) is for safety.

In India, the electric power supplied to homes has a potential difference of $220 \\text{ V}$ between the live and neutral wires, with a frequency of $50 \\text{ Hz}$.

Overloading occurs when the current drawn from a circuit exceeds its safety limit. This can be caused by connecting too many appliances to a single socket or a sudden voltage hike.

A short circuit occurs when the live wire and the neutral wire come into direct contact. This causes the resistance of the circuit to become very low, resulting in a very high current flow.

An electric fuse is a safety device containing a wire with a low melting point. It melts and breaks the circuit if the current exceeds a safe level, protecting appliances from damage due to overloading or short-circuiting.

The earth wire connects the metallic body of an appliance to the ground. It provides a low-resistance path for leakage current, preventing the user from getting an electric shock.