History of Magnets

1
History of Magnets

• Lodestone
• Always pointed in one direction (North)
• Use to keep ships on course.
• Magnetite (Fe3O4)
• First found in region of Asia--Magnesia

2
Types of Substances

• Magneticattracted to a magnet.
• Ferromagnetic
• become magnetic when
  placed in a magnetic field.
• Iron, nickel, cobalt
• Non magnetic

3
Magnetism

• Two poles
• North-Seeking
• South-Seeking
• Opposite poles attract
• Like poles repel

4
Earth is a magnet

• The Earth behaves like a giant bar magnet.
• Magnets are surrounded by a magnetic field.
• Fields exert forces on each otherlike
  gravitational and electric.

5
Compass

• When placed in the Earths magnetic field
• A bar magnet will align so that its north seeking
  pole faces Geographic North.
• A bar magnet will align itself so that its south
  seeking pole faces Geographic South.

6
Magnetism Basics

• Materials that contain iron, nickel, or cobalt
  are attracted to magnets.
• Permanent Magnets
• Ferromagnetic materials
• Temporary Magnets
• Certain metals can be induced to become magnetic
  for short periods of time.

7
How Do Magnets Work?

• All mass is surrounded by a gravitational field
• All charges are surrounded by an electric field.
• If a charge is moving, it is surrounded by a
  magnetic field.

8
Magnetic Field Strength vs. Electron Spin
Direction

• All atoms contain electrons that are in motion.
• Electrons spin in different directions and their
  magnetic fields cancel out.
• Electrons spin in the same direction and their
  magnetic fields strengthen.

9
Magnetic Domains

• In a magnet, clusters of atoms line up with each
  other as their electrons spin in the same
  direction.
• Microscopic clusters called domains.
• Difference between regular iron and magnetic iron
  is alignment of domains.

10
Temporary vs. Permanent Magnets

• If a ferromagnetic material is placed in a strong
  magnetic field, it will become a permanent magnet
  (Steel).
• If certain metals are brought into a magnetic
  field, their domains can align to form a
  temporary magnet (Iron).

11
How To Make a Magnet

• By Contact
• Iron becomes a temporary magnet.
• Steel becomes a permanent magnet.
• Why the difference?
• Which would you want your compass to be made
  from?
• By Induction
• By Electricity

12
How to Demagnetize a Magnet

• Heat
• Contact
• Hammering or Jarring

13
Magnets

• Because magnetism is produced by individual
  atoms, the two poles cannot be separated
  (difference from charge).

14
Magnetic Fields

• Moves from North to South
• Strongest at poles where field lines closest.
• Exert force on other magnetic fields
  (metals/other magnets)

15
Magnetic Fields
16
Magnetic Fields
17
Interaction of Magnetic Fields
18
Electric Current Produces Magnetism

• A spinning electron produces a magnetic field.
• Many charges in motion (electric current) can
  also produce a magnetic field.
• As charged particles (electrons) move through a
  wire, a magnetic field is created around that
  wire.

19
Electric Current Produces a Magnetic Field

• Right Hand Rule

20
Electric Current Produces Magnetism

• If a current carrying wire is bent into a loop,
  the electric field lines become concentrated
  inside the loop.

21
Electric Current Produces Magnetism

• As the number of loops is increased, the electric
  field from each loop adds together to produce a
  much stronger magnetic field.

22
Electromagnets

• If an iron core is placed at the center of the
  loops, the domains in the iron will align with
  the magnetic field, creating an electromagnet.

23
Electromagnets
24
Strength of an Electromagnet

• Number of coils
• Current
• Thickness of core
• Applications
• Speakers
• Telephones
• Motors and engines
• Electric guitar
• Maglev trains
• Television

25
Magnetic Field Exerts Force On Moving Charges

• When a charged particle moves through a magnetic
  field, it feels a force.
• Force, magnetic field, current all perpendicular
  to each other.

26
Speakers

• This is the principle behind speakers.
• Current passes through wire that is placed near a
  magnet.
• As current moving through wire alternates, polar
  orientation of magnetic field changes.
• As orientation changes, the direction of the
  force changes.
• Creates vibration attach wire to cone?sound

27
Speakers
Click for Animation
28
Motor

• Converts Electrical Energy to Mechanical Energy.
• Consists of a permanent magnet, and an
  electromagnet (the armature/rotor)

29
Motor

• When electric current runs through the wire, the
  armature becomes magnetized.

30
Motor

• The north end of the armature is attracted to the
  south pole of the permanent magnet.
• The south end of the armature is attracted to the
  north pole of the permanent magnet

31
Motor

• After half a turn, the direction of the current
  is reversed causing the poles on the
  electromagnet to reverse and rotation to occur.

32
Motor
33
Motor
Click for Animation
34
Generator

• 1831Michael Faraday found that it is possible to
  obtain electricity from magnetism.
• Placed a permanent magnet in a coil of wire.
• Movement produces current.
• Electric current?magnetic field
• Magnetic field?electric current

35
Generator

• Electromagnetic Induction
• Producing current by moving a magnet through a
  coil of wire.
• Produces alternating current (AC)

36
Generator

• Converts mechanical energy to electrical energy.
• Works in opposite fashion as a motor.

37
Generator

• A loop of wire is rotated through a magnetic
  field.
• Through the relative movement
  between the wire
  and the electric
  field, electrons feel
  a force.
• Electrons move,
  producing current.

38
Generator

• What energy sources can we use to produce
  mechanical energy to turn the metal loop?

Click for Animation
39
Transformers

• A device used to increase or decrease voltage by
  electromagnetic induction.
• Electricity is carried over
  long distances at a high
  voltage.
• Voltage must be stepped
  up at the power plant.
• Voltage must be
  stepped down at
  your house.

40
Transformers

• Power plant 6000V
• Long distance transmission 120,000V
• City transmission 2200V
• Household Circuits 120V

41
Transformers

• Primary Coil (input)
• Secondary Coil (output)
• Wires wrapped around iron core.
• Input current magnetizes iron.

42
Transformers

• Magnetic field around Iron induces current in
  secondary coils.

43
Transformers

• If the secondary coil has more coils than the
  primary coil.
• Voltage out is greater than voltage in
• Step Up Transformer

44
Transformers

• If the secondary coil has fewer coils than the
  primary coil
• Voltage out is less than voltage in
• Step Down Transformer

45
Transformers

• If energy cannot be created, than how can the
  voltage output be greater than the voltage input?
• Answer
• As the voltage is increased, the current is
  subsequently decreased.

46
Transformer Formulas

• .
• (Voltage x Current)primary (Voltage x
  Current)secondary
• Power in Power out
• Energy is conserved

47
Transformer Example Problem

• A transformer receives a current at 150V. The
  primary coil has 50 turns, the secondary coil has
  100 turns.
• What is the output voltage?
• Is this a step-up or step-down transformer?