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The regoin around a magnet in which this magnetic effect can be detected
All magnetic fields
start from N pole and end at the S pole
lines cannot cross each other
have lines that are closer together in a stronger magnetic field
A magnetic field can be mapped by using a plotting compass to trace the field line
a neutral point is a place where the resultant magnetic field strength is zero.
Law of Magnetism
Like poles repel,unlike poles attract
North and south pole
If a magnet is allowed to hang freely,it will come to rest in the North-South direction
The end pointing to the Northern end of thr Earth is the North-seeking pole
Every magnet has a North and south pole.
These are the strongest parts of the magnet
They are found very near to the ends of the magnet.
Attract Magnetic stuff
Steel is more difficult to demagnetised
Steel is usually used to make permanent magnet
Iron is easier to demagnetised
Iron is usually used to make temporary magnet
Theory of Magnetism
In magnetic materials,millions of neighbouring atoms align themselves ingroups each point in a certain direction
Each of these groips is called domain. When they are being magnetised the domain are aligned in the same direction.
1.Occurs when non magnetised material is brought near a magnet
2.Magnetic material will be come a weak magnet
3.The pole of the non-material being induced will be opposite of the magnet inducing
Magnetisation by Stroking
the end of the object(e.g steel bar) where the stroke finishes has the opposite polarity to that of the stroking magnet in contact with it.
Magnetisation using direct current
object is placed inside a solenoid which has a direct current passed through it to magnetise the object
Demagnetisation Using Alternating Current
a low alternating current is flowed through a solenoid which has the magnet tobe demagnetised incontact with it.
Demagnetisation by heating and Hammering
if a magnet is hammered vigorously or heated to red-hot its magnetism will become weaker or dissapear.
Magnetic Properties of Iron and steel
Iron is easy to magnetise but loses its magnetism easily
soft magnetic material (temporary magnets)
Steel is hard to magnetise but does not lose its magnetism easily.
hard magnetic material (permanent magnets)
Uses of permanent magnets
Magnetic door catches
Refridgerator door seals
consist of a coil made from several hundred turns of insulated copper wire wound on a core of soft magnetic material like soft iron
When switch closed, curent flows through the coil and the core becomes magnetised.
When circuit is open, no more current flows through the coil, the soft iron core loses its magnetism
Magnetic field strength can be increased by
passing larger current through the coil
increasing the number of turns of the coil
inserting a core made of soft magnetic materials
Sorting scrap metal
Audio and video tapes
Credit,debit and ATM cards
Television and computer monitor