Download Power point on Magnetism - EMS Secondary Department

PROPERTIES OF MAGNETS
1. ALL magnets have NORTH and south poles.
2. When freely suspended, all magnets point to the northDirectional property.
NORTH seeking pole
SOUTH seeking pole
Magnetic materials.
Materials that can be attracted by a
magnet. These include:
Iron(steel), Nickel, Cobalt or their
alloys ONLY.
• Non-magnetic materials.
• Materials that do not feel a magnetic
force.
Example: wood, copper, aluminium,
rubber, water, wool, paper,
FEROUS MATERIALS
• Ferrous materials are materials that contain
iron in them.
• Example: Steel, stainless steel, invar.
• Most ferrous materials are magnetic.
NON-FERROUS MATERIALS
• These are materials that do not contain iron
in them.
• Example: Nickel and cobalt which are
magnetic.
• Most non-ferrous materials are non-magnetic.
THE LAW OF MAGNETISM
• Like poles repel, unlike
poles attract.
Breaking a magnet produces two magnets.
N
S
N
S
N
S
N
Repeated
breaking will
create a
smallest magnet
atomic
magnet(dipole)
S
Un-magnetized
material
Domains are not
arranged in any
order.
• Magnetized
material
• Domain aligned
in one direction.
MAGNETIZATION
• A process of making of magnets.
• There are 3 methods of
magnetising;
• 1. Stroking or touching.
• 2. Electrical method.
• 3. Magnetic induction.
Methods of magnetization
Magnetic induction
When a magnetic material is close to a
magnet, it becomes a magnet itself
magnet
S
N
S
We say it has induced magnetism
N
Soft Magnetism
Pure iron is a soft magnetic material
before
S
N
S
after
N
S
NN
Not a
magnet
Iron nail
It is easy to magnetise iron but loses its
magnetism easily.
It is used to make (temporal) electromagnets
Hard Magnetism
Steel is a hard magnetic material
before
S
after
N
S
S
NN
S
N
Steel paper
clip
It is harder to magnetise, but keeps its
magnetism (it is used to make permanent
magnets!)
N
It’s a
magnet!
Magnetic fields
The space around a magnet where it’s
magnetic force is felt.
The magnetic field is shown by field lines
running from North pole to south pole
Magnetic field Patterns
A magnet has strong field at the
poles.
ELECTROMAGNETS
• An ELECTROMAGNET is a magnet
that can be switched on and off by
an electric current.
Switch On: Current
flows and the nails
becomes a magnet.
Switch Off: No
current and the nail
looses its
magnetism.
Increasing the strength of
electromagnets
• 1. Increase amount of current.
–More current produces stronger
electromagnet
• 2. Increase number turns of the
coil.
• 3. Using soft Iron core.
Uses of electromagnets
1. Used in lifting scrap metal
2. Used in many electronic
devices such es electric bell,
electric relay, loud speakers,
etc.