Magnetic Field and Field Lines
Hans Christian Oersted accidentally discovered that a compass needle gets deflected when placed near a current-carrying wire, proving that electricity and magnetism are linked. The region around a magnet where its influence can be felt is called the Magnetic Field.
Magnetic Field Lines are imaginary curves that represent the direction and strength of the magnetic field. Properties of magnetic field lines include:
- They emerge from the North pole and merge at the South pole (outside the magnet).
- Inside the magnet, their direction is from South to North, forming closed loops.
- The closer the lines, the stronger the magnetic field.
- Two magnetic field lines never intersect each other.
Magnetic Field due to Current-Carrying Conductors
The magnetic field produced by a straight current-carrying wire forms concentric circles around the wire. The direction of the field is given by the Right-Hand Thumb Rule: if you grasp the wire with your right hand such that the thumb points in the direction of the current, your curled fingers indicate the direction of the magnetic field.
A coil of many circular turns of insulated copper wire wrapped closely in the shape of a cylinder is called a Solenoid. The magnetic field inside a current-carrying solenoid is uniform and similar to that of a bar magnet. Placing a soft iron core inside a solenoid produces a powerful Electromagnet.
Force on a Current-Carrying Conductor
When a current-carrying conductor is placed in a magnetic field, it experiences a mechanical force. The direction of this force is given by Fleming's Left-Hand Rule: stretch the thumb, forefinger, and middle finger of your left hand mutually perpendicular to each other. If the forefinger points to the magnetic field and the middle finger points to the current, the thumb will point in the direction of the force (or motion).
The Electric Motor
An electric motor is a device that converts electrical energy into mechanical energy. It works on the principle that a current-carrying rectangular coil placed in a magnetic field experiences a torque that causes it to rotate continuously. A commutator (split-ring) reverses the direction of current in the coil every half rotation to maintain continuous rotation.
Electromagnetic Induction and Generators
Michael Faraday discovered that a changing magnetic field near a conductor induces an electric current in the conductor. This phenomenon is called Electromagnetic Induction. The direction of induced current is given by Fleming's Right-Hand Rule.
An Electric Generator uses this principle to convert mechanical energy into electrical energy. It consists of a rotating coil in a magnetic field. Depending on the arrangement of rings, it can produce Alternating Current (AC), which changes direction periodically, or Direct Current (DC), which flows in only one direction.