Download Magnetism

Magnetism
Keywords
What is magnetism?
Force of attraction or
repulsion due to
electrons.
Magnetic forces are the
strongest at the poles
Magnets have two
poles: North and South
Properties of magnets
Magnets always have two
poles
If a magnet is cut it will still
have two poles
Like magnetic poles repel
Unlike magnetic poles attract
A magnetic field is the area in
which magnetic forces act
Magnet properties
A freely suppended
bar magnet will
always it always
comes to rest in a
north south
direction.
The end pointing
north is called a
north pole.
Questions
What two forces are involved in
magnetism?
Which subatomic particle accounts for
magnetism?
Explain the interaction between
magnetic poles when they are close
together.
To what use is a freely swinging magnet
put to?
Magnetic materials
Natural magnets have naturally
occurring magnetic properties e.g.:
LODESTONE (magnetite)
The elements iron, nickel and
cobalt only can be magnetised.
Alloys like steel and alnico make
strong man-made magnets
Earth’s magnetic properties
Gilbert was a scientist that showed
that the Earth behaves as a magnet
The Earth’s magnetic field is
strongest at the poles
The Earth’s magnetic field behaves
as if there is a huge bar magnet in
it’s centre.
The Earth’s magnetic field
Compasses
Compasses are used to determine
direction
Compass needles are magnetized
and respond to the magnetic field
of the Earth
Compasses point to the
MAGNETIC POLES OF THE
EARTH
Questions
Which scientist described the
Earth’s magnetic properties?
Name the devices used to
indicate geographic direction
based on the Earth’s magnetic
field.
Magnetic effect of an electric current
Discovered by
Oersted (scientist)
When an electric
current flows in a
wire it creates a
magnetic field
around it.
Questions
Who discovered the magnetic effect of
an electric current?
What happens the compass needle
when the current is switched on?
Name one practical application of this
effect?
Electromagnets
Temporary magnets
Magnetism can be turned on and
off
Made by wrapping wire around a
piece of iron and sending a current
through the wire
Magnetic field is in the same
direction as the electric current
A simple electromagnet
When the power is
switched on the nail
becomes a magnet
and when it is
switched off it loses it’s
magnetism.
Questions
What is electromagnetism?
What type of magnet is an
electromagnet?
If the current is switched off is the
nail magnetic?
Uses of Magnets
Used in compasses
Body scans in hospitals (NMR)
electric motors, electric bells, tranformers,
loudspeakers, telephones, computers and
microwave ovens all use magnets.
In door catchs for fridges and presses.
In magnetic ink on cash cards.
Electromagnets used in scrapyards to move
scrap iron.