Magnetism is caused by the alignment of electron spins in atoms. Natural magnets were first discovered in Magnesia, and the Chinese were the first to observe that magnetism could be induced in iron rods near these natural magnets. Michael Faraday established that changing magnetic fields induce electric currents based on electromagnetic induction. This principle led to technologies like generators and transformers that are crucial to modern electricity generation and distribution.

1. MAGNETISM
A Strangely Attractive Topic

2. HISTORY
 Term
comes from the ancient Greek city of
Magnesia, at which many natural magnets
were found.
 We now refer to these natural magnets as
lodestones (lode means to lead or to attract)
which contain magnetite, a natural magnetic
material Fe3O4.

3. HISTORY
 Pliny
the Elder (23-79 AD Roman) wrote of a hill
near the river Indus that was made entirely of a
stone that attracted iron.

4. HISTORY
 Chinese
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
north-south direction.
 Use of magnets to aid in navigation can be
traced back to at least the eleventh century.

5. HISTORY
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?
 Magnetism
is the force of
attraction or repulsion of
a magnetic material due
to the arrangement of its
atoms,
particularly its
electrons.

7. What causes magnetism?
 Atoms
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?
 When
an unmagnetized substance is placed in a
magnetic field, the substance can become
magnetized.
 This happens when the spinning electrons line up
in the same direction.

9. What causes magnetism?
 An
unmagnetized substance looks like this…
 While
a magnetized substance looks like this…

10. How to “break” a magnet?
 Drop
it.
 Heat
it.
 This
causes the domains to
become random again!

11. A big natural magnet..
 It
exerts magnetic
forces and is
surrounded by a
magnetic field that
is strongest near the
North and South
magnetic poles.
Magnetic South Pole
Geographic South Pole
Geographic North Pole
Magnetic North Pole

12. PROPERTIES OF MAGNETS
 There
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
 Every
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.
 No
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.
 It
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
 Michael
Faraday realized that a magnet has a
„magnetic field‟ distributed throughout the
surrounding space.
 This
field exerts a force on any charge/magnetic
material on it.

16. 2. Magnetic Fields, cont.
 Field
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
 LAW
of MAGNETISM: Like poles repel, unlike poles
attract.

18. 4. Attract only magnetic materials

Magnets only attract certain types of metals, other
materials such as glass, plastic and wood aren't
attracted.

Metals such as iron, nickel and cobalt are attracted
to magnets.

Most metals however are not attracted to
magnets,
these
include
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
them away.

19. 5. Action at a Distance
 Although
two magnets
may not be
touching, they still
interact through their
magnetic fields.
 This
explains the
„action at a
distance‟, say of a
compass.

21. Electricity to Magnetism
Hans Oersted


first observed that a current in a wire affects a
nearby compass needle
Implication: an electric current creates a
magnetic field

22. Electromagnets
- Magnets created using a current
Magnetic strength increases with:
 more current in the wire
 more coils of wire
 bigger ferromagnetic core

23. Uses of Electromagnetism
1. Electric motors
 Converts electrical energy to mechanical energy
 Anytime electricity is converted into a motion its
through an electric motor

24. Uses of Electromagnetism
2. Current meters
 Galvanometer – used to measure small currents
 Ammeter – used to measure currents
 Voltmeter – used to measure voltage

25. Magnetism to Electricity
Michael Faraday


if an electric current can create a magnetic
field, then maybe a magnetic field can create a
electric current
this led to his Law of Electromagnetic Induction

26. Law of Electromagnetic Induction
 Any
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

27. Uses of Electromagnetic Induction
1. Generator
 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
thermoelectric (heat)

28. Uses of Electromagnetic Induction
2. Transformer
 Used to increase or decrease
voltage/current
 Step-up or Step-down
 High voltage electricity is
used in long distance
transmission
 Low voltage is used in homes