10Properties of Magnets Testing a magnet 1. Bring one end of an unknown object to a suspended magnet.2. If repulsion occurs, then the unknown object is a magnet since repulsion occurs between like poles.
11Magnetic InductionMagnetic Induction is the process of inducing magnetism in an unmagnetised ferromagnetic material without any contact with the magnet.
12Induced MagnetismMaking of magnetic materials (e.g. steel and Iron) into MagnetsInducing magnetism in an ordinary piece of magnetic materialInduced magnetism is a temporary process
13Induced MagnetismThe two iron nails become induced magnets and show a repulsion between the far ends
14Induced MagnetismRepulsion between the two iron nails increases as a bar magnet is brought towards the nails
15MAGNETIC POLES A magnet is a dipole (two pole) There is no monopole (single pole)
16MAGNETIC POLES A magnet is a dipole (two pole) There is no monopole (single pole)
17Magnetic Materials Most materials are NOT magnetic Naturally occurring magnetic materials are called FERROMAGNETIC (Iron-Like)FERROMAGNETIC MATERIALS areIron, SteelCobaltNickelAlloys of above metals
18Magnetic Domains These are small regions in a FERROMAGNETIC Material where all the magnetic fields of the atoms are aligned
19MagnetizationSNIf the domains are aligned, the material is polarized and becomes magnetized
41Magnetic Properties of Iron & Steel (soft Magnet)Steel(Hard Magnet)Easy to magnetizeCan be magnetized by a weak magnetic fieldHarder to magnetizeRequired a strong magnetic field to magnetiseEasy to demagnetizeHarder to demagnetizeUsed in Electromagnets, transformer cores and magnetic shieldsGood in making permanent magnets and bar magnets
54Magnetic Field due to a solenoid The strength of the magnetic field can beincreased by:Increasing the currentIncreasing the number of turns per unit length of the solenoidUsing a soft-iron core within the solenoid
55Magnetic Field due to a solenoid Electromagnets are far more useful than permanent magnets because:They can be switched on and off.2. The strength of the magnetic field can be changed, by altering the current.3. They can easily be made into a variety of shapes and are less expensive to make
57Uses of electromagnets The electric Bell-The current flows in the coilmaking an electromagnet-The armature is attracted tothe core-As it moves, the circuit isbroken at the contact screw.-The electromagnet is switchedoff, so the armature moves back.The armature keeps vibratingback and forth making thehammer strike the gong.
58Uses of electromagnets Magnetic RelayRelays are used as safety devices.A large current circuit can be switched on by a small current circuitWhen the small current/voltage (that is safe) in the input circuit is switched on, the electromagnet becomes magnetic and attracts the iron armature.The armature rotates towards the electromagnet, pushing the contacts together. This switches on the large current/voltage (that is dangerous) in the output circuit.This type of relay circuit is used in the ignition of a car.