Permanent and Induced Magnets Magnets can be classified as either permanent or induced. Permanent magnets are objects made from materials like iron, nickel, cob...
Permanent and Induced Magnets
Magnets can be classified as either permanent or induced. Permanent magnets are objects made from materials like iron, nickel, cobalt, or rare earth metals that generate their own persistent magnetic field. Induced magnets are temporarily magnetized by the magnetic field surrounding them.
Magnetic Fields
A magnetic field is the area around a magnet where magnetic forces can be detected. Magnetic field lines represent the direction of the net magnetic force at any given point.
The direction of magnetic field lines outside a bar magnet emerge from the N-pole and enter the S-pole.
The Earth's magnetic field causes a freely suspended magnet to align in a N-S direction.
Magnetic Fields and Currents
An electric current flowing through a wire creates a circular magnetic field around the wire. The direction of this magnetic field is given by the right-hand grip rule.
The strength of the field depends on the current and number of turns in a coil (solenoid).
The motor effect describes the force on a current-carrying wire in a magnetic field.
Fleming's Left-Hand Rule: Relating the force (F), current (I), and magnetic field (B) vectors.
Force on a Motor Coil Example
Problem: Calculate the force on a 0.2 m long wire carrying 3 A of current in a 0.5 T magnetic field.
Solution:
Given: L = 0.2 m, I = 3 A, B = 0.5 T
Using F = BIL, F = 0.5 × 3 × 0.2 = 0.3 N
Electromagnetic Induction
Changing magnetic fields can induce electric currents in conductors - this is called electromagnetic induction and is the generator effect.
Generators and alternators use this principle to produce AC currents by rotating a coil in a magnetic field.
Transformers use induction to step up/down AC voltages for efficient transmission.
The National Grid transmits electrical energy over long distances using transformers.