Chapter 12: Magnetic Effects of Electric Current
Magnetic Fields and Field Lines
An electric current produces a magnetic field around it, discovered by Hans Christian Oersted. This field can be visualized using iron filings or compass needles. The direction of the magnetic field is defined as the direction a north pole of a compass would point and is represented by field lines. These lines emerge from the north pole and enter the south pole of a magnet, forming closed loops. The closeness of the field lines indicates the strength of the field. Two magnetic field lines never cross each other.
Magnetic Effects of Current-Carrying Conductors
The magnetic field around a straight current-carrying conductor consists of concentric circles and its direction follows the right-hand thumb rule. When the conductor is bent into a circular loop, the field becomes stronger at the center. In a solenoid—a coil of wire—the magnetic field is uniform inside and resembles that of a bar magnet. A solenoid with a soft iron core becomes an electromagnet. The strength of the field depends on the current, number of turns, and the core material.
Force, Domestic Circuits, and Safety
A current-carrying conductor placed in a magnetic field experiences a force, whose direction is given by Fleming’s left-hand rule. This principle is used in devices like electric motors. In homes, electric circuits involve live (red), neutral (black), and earth (green) wires. Safety devices like fuses protect against overloading and short circuits, which can occur when too many appliances are connected or due to damaged insulation. Earth wires prevent electric shocks by safely redirecting leaked current into the ground.