comes from the ancient Greek city of
Magnesia, at which many natural magnets
We now refer to these natural magnets as
lodestones (lode means to lead or to attract)
which contain magnetite, a natural magnetic
the Elder (23-79 AD Roman) wrote of a hill
near the river Indus that was made entirely of a
stone that attracted iron.
as early as 121 AD knew that an iron rod
which had been brought near one of these
natural magnets would acquire and retain the
magnetic property, and that such a rod when
suspended from a string would align itself in a
Use of magnets to aid in navigation can be
traced back to at least the eleventh century.
Basically, we knew the phenomenon existed
and we learned useful applications for it.
We did not understand it.
Not until its connection to electrical charges and
currents was discovered.
6. What is magnetism?
is the force of
attraction or repulsion of
a magnetic material due
to the arrangement of its
7. What causes magnetism?
themselves have magnetic properties
due to the spin of the atom‟s electrons.
Groups of atoms join so that their magnetic fields
are all going in the same direction.
These areas of atoms are called “domains”.
8. What causes magnetism?
an unmagnetized substance is placed in a
magnetic field, the substance can become
This happens when the spinning electrons line up
in the same direction.
9. What causes magnetism?
unmagnetized substance looks like this…
a magnetized substance looks like this…
10. How to “break” a magnet?
causes the domains to
become random again!
11. A big natural magnet..
forces and is
surrounded by a
magnetic field that
is strongest near the
North and South
Magnetic South Pole
Geographic South Pole
Geographic North Pole
Magnetic North Pole
12. PROPERTIES OF MAGNETS
are north poles and south poles.
Magnets set up a magnetic field around it.
Like poles repel, unlike poles attract.
Magnetic forces attract only magnetic materials.
Magnetic forces act at a distance.
13. 1. North and South Poles
magnet has at least one north pole and
one south pole.
If you take a bar magnet and break it into two
pieces, each piece will again have a north pole
and a south pole.
matter how small the pieces of the magnet
become, each piece will have a north pole and
a south pole.
14. 1. North and South Poles, cont.
has not been shown to be possible to end up
with a single North pole or a single South
pole, which is a monopole ("mono" means one
or single, thus one pole).
15. 2. Magnetic Fields
Faraday realized that a magnet has a
„magnetic field‟ distributed throughout the
field exerts a force on any charge/magnetic
material on it.
16. 2. Magnetic Fields, cont.
lines converge where the magnetic force is
strong, and spread out where it is weak. In a
compact bar magnet or dipole, field lines
spread out from one pole and converge
towards the other.
17. 3. Like poles, unlike poles
of MAGNETISM: Like poles repel, unlike poles
18. 4. Attract only magnetic materials
Magnets only attract certain types of metals, other
materials such as glass, plastic and wood aren't
Metals such as iron, nickel and cobalt are attracted
Most metals however are not attracted to
copper, silver, gold, magnesium, platinum, aluminium
and more. They may however magnetize a small
amount while placed in a magnetic field.
Magnetism can attract magnetic objects or push
19. 5. Action at a Distance
may not be
touching, they still
interact through their
„action at a
distance‟, say of a
20. Electricity to Magnetism
first observed that a current in a wire affects a
nearby compass needle
Implication: an electric current creates a
- Magnets created using a current
Magnetic strength increases with:
more current in the wire
more coils of wire
bigger ferromagnetic core
22. Uses of Electromagnetism
1. Electric motors
Converts electrical energy to mechanical energy
Anytime electricity is converted into a motion its
through an electric motor
23. Uses of Electromagnetism
2. Current meters
Galvanometer – used to measure small currents
Ammeter – used to measure currents
Voltmeter – used to measure voltage
24. Magnetism to Electricity
if an electric current can create a magnetic
field, then maybe a magnetic field can create a
this led to his Law of Electromagnetic Induction
25. Law of Electromagnetic Induction
change in the magnetic field of a coil of
wire will cause a voltage to be induced in the
coil, called the induced voltage.
If the conductor circuit is closed, the current will
also circulate through the circuit and this current
is called induced current.
How to increase induced voltage/current
Increase number of coils
Increase magnetic field
Increase speed of relative motion between coil
and magnetic field
26. Uses of Electromagnetic Induction
Converts mechanical energy to electrical energy
Used in most power plants to create electricity
In coal, oil, natural gas, nuclear or geothermal
power plants, the heat is used to boil water into
steam which is then used to rotate the turbines
In wind, hydroelectric (dam/falls) and tidal power
plants, the turbines are rotated by the wind/water
The only sources of electricity that does not use
generators are solar, chemical
(batteries), piezoelectric (crystals) and
27. Uses of Electromagnetic Induction
Used to increase or decrease
Step-up or Step-down
High voltage electricity is
used in long distance
Low voltage is used in homes