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Exploring the Science of Electricity

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Title: PowerPoint Presentation Author: Larry Pfieffer Last modified by: Aaron Albisu Created Date: 2/14/2000 2:58:12 PM Document presentation format – PowerPoint PPT presentation

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Title: Exploring the Science of Electricity


1
Lesson
  • Exploring the Science of Electricity

2
Interest Approach
  • What is Electricity?
  • Where does electricity come from?
  • How does it get from its source to where we use
    it?

3
Interest Approach
  • What happens when you walk across carpet in the
    winter and receive a shock when you touch
    someone or something metal?

4
Interest Approach
  • Static electricity is actually a transfer of
    electrons from you to the object you touch

5
Student Learning Objectives
  • Relate electricity to the structure of elements
    and atoms.
  • Explain conductors, insulators, and
    semiconductors.
  • Explain the conventional and electron theories of
    electrical current flow.

6
Student Learning Objectives
  • Describe how electricity can be generated by
    friction, heat, light, chemical reactions, and
    magnetism.
  • Describe the difference between and applications
    of direct current (DC) and alternating current
    (AC) electricity.

7
Terms
  • Alternating current
  • Atoms
  • Battery
  • Conductors
  • Conventional theory
  • Cycle
  • Direct current
  • Electricity
  • Electrodes
  • Electrolyte
  • Electromagnet
  • Electron theory
  • Electrons
  • Elements
  • Free electrons
  • Friction
  • Fuel cell
  • Hertz
  • Insulators

8
Terms
  • Magnetic induction
  • Neutrons
  • Photovoltaic effect
  • Polarity
  • Primary batteries
  • Protons
  • Secondary batteries
  • Semiconductors
  • Solar (photo) cell
  • Synchronous alternator
  • Thermocouple
  • Thermopile
  • Valence

9
Objective 1
  • How does electricity relate to the structure to
    of elements and atoms?

10
Elements
  • Elements are substances that cannot be broken
    down into simpler substances using ordinary
    chemical methods.
  • All matter is composed of one or more elements.

11
Atoms
  • Atoms are the smallest units of an element.
  • They cannot be divided further without losing
    physical and chemical properties.
  • Atoms are composed of protons, neutrons, and
    electrons.

12
Protons and Neutrons
  • Protons have a positive electrical charge, while
    neutrons have no electrical charge.

13
Protons and Neutrons
  • Protons and neutrons make up the nucleus, or
    center of each atom.
  • Thus the nucleus of each atom has a positive
    electrical charge.

14
Electrons
  • Electrons have a negative electrical charge and
    orbit the nucleus of an atom in rings or shells.
  • Since unlike charges attract each other, the
    electrons are held in orbit by the positively
    charged nucleus.

15
Electrons
  • The outer ring of electrons is called the valence
    ring.

16
Copper As A Conductor
  • The element copper, has 29 protons in its nucleus
    and 29 electrons which orbit its nucleus.
  • The electrical charges cancel each other.

17
Artwork supplied with permission of Interstate
Publishers, Inc.
18
Copper as a Conductor
  • The electrons actually orbit the nucleus in
    rings.
  • The first or inner ring can hold a maximum of 2
    electrons, the second ring, a maximum of 8
    electrons, the third ring, a maximum of 18, the
    fourth ring, a maximum of 32, the fifth ring, a
    maximum of 50, and the sixth, a maximum of 72.

19
Copper as a Conductor
  • Generally, the rings closest to the nucleus are
    filled before additional rings are started.
  • Thus, copper has 1 electron in the fourth ring or
    valence ring (2 8 18 1).

20
Copper as a Conductor
  • The number of electrons in the valence ring has
    a key role in determining the electrical
    characteristics of the element.

21
Free Electrons moving between copper atoms
Artwork supplied with permission of Interstate
Publishers, Inc.
22
What are conductors, insulators, and
semiconductors?
  • Objective 2

23
Conductors, Insulators, and Semiconductors
  • Conductors, insulators, and semiconductors are
    important in electricity and electronics.
  • The following will help explain each

24
Conductors
  • Materials that allow electricity to flow through
    them easily.
  • Copper, aluminum, silver, and gold are good
    conductors.

25
Conductors
  • Generally, nearly all metals are good electrical
    conductors.
  • Any element or material having atoms with three
    or fewer electrons in its valence ring will be a
    conductor.

26
Insulators
  • Materials that do not allow electricity to flow
    through them under normal conditions.
  • Materials such as rubber, plastic, porcelain, and
    glass are all good electrical insulators.

27
Insulators
  • Any element or material composed of atoms having
    five or more electrons in the valence ring will
    be an insulator.
  • Insulators are used to confine the flow of
    electricity to desired paths.

28
Semiconductors
  • Materials that are neither good conductors nor
    good insulators.
  • Semiconductors are manufactured from elements
    having atoms with four electrons in their valence
    rings.
  • Silicon and germanium are widely used in making
    semi-conducting materials.

29
Objective 3
  • What are the conventional and electron theories
    of electrical current flow?

30
Electricity
  • Electricity is the flow of electrons from atom to
    atom in a conductor.
  • There are two different theories to help describe
    electricity

31
Conventional Theory
  • Says that electricity is the flow of positively
    charged particles through a conductor.
  • This is the older theory and was developed before
    scientists discovered the existence of electrons.
  • With this theory, it was assumed that current
    flow in an electrical circuit was from positive
    to negative.

32
The direction of current flow according to
theconventional theory.
Artwork supplied with permission of Interstate
Publishers, Inc.
33
Electron Theory
  • This is the accepted model of electrical current
    flow, however, because of tradition, the
    conventional theory is still widely used.
  • Either theory may be used as long as it is used
    consistently.

34
Electron Theory
  • The electron theory says that electricity is the
    flow of electrons through a conductor.
  • Remember conductors have three or fewer electrons
    in their valence ring.

35
Electron Theory
  • When there are so few electrons in the valence
    ring they are not held very tightly.
  • These free electrons can be dislodged if
    sufficient external force is applied.

36
Electron Theory
  • An example of external force is a battery, which
    has a positive terminal and a negative terminal.

37
The direction of current flow according to the
electron theory.
Artwork supplied with permission of Interstate
Publishers, Inc.
38
Electron Theory
  • Since unlike charges attract each other, if a
    copper wire were attached to the two terminals,
    the negatively charged free electrons would be
    dislodged and pushed by the negative terminal and
    pulled by the positive terminal of the battery,
    causing the electrons to flow.
  • This would continue until the battery discharges.

39
How can electricity be generated by friction,
heat, light, chemical reactions, and magnetism?
  • Objective 4

40
How can electricity be generated by friction,
heat, light, chemical reactions, and magnetism?
  • An external force must be applied to cause free
    electrons to flow through a conductor.
  • This force is the production or generation of
    electricity, which can be generated in the
    following ways

41
Friction
  • Friction is caused when two or more materials rub
    against each other.

42
Friction
  • When this happens, some of the free electrons
    from one material are transferred to the other
    material, causing one of the materials to have a
    positive electrical charge and the other to have
    a negative electrical charge.

43
Friction
  • When the negatively charged material touches a
    material with a neutral or positive charge, the
    excess electrons will flow to the second object.

44
Friction
  • This can be demonstrated when you walk across
    carpet in the wintertime.
  • As you walk across the carpet, the soles of your
    shoes rub over the carpet which transfers
    electrons from the carpet to your body.

45
Friction
  • When you touch someone else or a doorknob, the
    excess electrons discharge through your hands
    resulting in a static electricity shock.
  • Friction is not a practical method of generating
    electricity.

46
Thermocouple
  • Heat or temperature differences can be used to
    generate electricity using a thermocouple.
  • A thermocouple consists of two dissimilar metals,
    such as iron and nickel, joined together to form
    two junctions.

47
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48
Thermocouple
  • When heat is applied to one of the junctions, the
    difference in temperature between the junctions
    causes free electrons to flow from the iron wire
    into the nickel wire and away from the hot
    junction toward the cold junction.

49
Thermocouple
  • To increase output, several thermocouples are
    often combined to form a device called a
    thermopile.
  • These are often used in flame detectors, furnace
    safety valves, and in precision heat measurement
    devices.

50
Photovoltaic Effect
  • Light from the sun can also be used to generate
    electricity.
  • It requires a solar (or photo) cell for
    converting the light into electricity through a
    process known as the photovoltaic effect.

51
Photovoltaic Effect
  • Certain materials (such as gallium, silicon, and
    cadmium sulfide) will convert light energy into
    electrical energy through the photovoltaic
    effect.
  • The solar cell is made of a thin disk of silicon
    to which other chemicals have been added.

52
Photovoltaic Effect
  • When light strikes the disk, electrons move from
    one side to the other side.
  • The electrons move through the conductors and
    provide electrical energy to power the circuit
    load(s).
  • Solar energy is used to power to such things as
    calculators and electric fence controllers.

53
Chemical
  • Reactions between certain chemicals can be used
    to produce electricity.

54
Chemical
  • First, a battery is made of two or more chemical
    cells connected together.
  • Each cell is composed of two dissimilar metal
    plates called electrodes.
  • They are separated from each other and immersed
    in an electrolyte.

55
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56
Chemical
  • An electrolyte is a chemical solution that
    contains positively and negatively charged atoms
    called ions.

57
Chemical
  • Using a chemical cell that is composed of a zinc
    plate, a copper plate, and an electrolyte
    solution of sulfuric acid and water as an
    example, the acid/water solution reacts with the
    zinc plate causing it to lose positively charged
    ions.

58
Chemical
  • Each positive ion lost leaves behind two
    electrons.
  • Thus, the zinc plate soon takes on a negative
    charge.
  • It then becomes the negative terminal of the
    cell.

59
Chemical
  • As the positive ions move through the
    electrolyte, they collide with the copper plate.
  • The positive ions attract free electrons from
    the copper plate.

60
Chemical
  • Thus, the copper plate soon takes on a positive
    charge due to this loss of electrons and becomes
    the positive terminal of the cell.

61
Chemical
  • If we connect a conductor to the two terminals,
    electrons will flow through the conductor from
    the zinc plate to the copper plate.

62
Chemical
  • This flow will continue until the difference in
    charge between the two plates has dissipated.
  • Once this happens, the cell will be discharged.

63
Chemical
  • Batteries may be classified as primary batteries
    (carbon-zinc, alkaline, and mercury) which cannot
    be recharged or as secondary batteries (lead-acid
    and nickel-cadmium) which can be recharged.

64
Chemical
  • A second chemical reaction to produce electricity
    is a fuel cell, which is similar to a battery,
    but different in the way the chemicals are
    supplied.

65
Chemical
  • In a battery, the chemicals are built in.
  • In a fuel cell, the chemicals are pumped into the
    cell from an external source.
  • Currently, fuel cells are limited to military and
    space applications.

66
Magnetism
  • The final method of generating electricity
    discussed here will be that of magnetism.

67
Magnetism
  • If a bar magnet is suspended freely from a
    string, the magnet will turn until one end points
    north and the other end points south.
  • The end pointing north is said to be the north
    pole of the magnet and the end pointing south the
    south pole.

68
Magnetism
  • An electromagnet may also be created using
    electricity.
  • If electricity flows through an insulated
    conductor that is wound around a metal object,
    the metal object will become a magnet.

69
Magnetism
  • Any time a conductor cuts across a magnetic field
    or a magnetic field cuts across a conductor,
    electricity will flow in the conductor.
  • Electricity generated in this manner is produced
    through the process of magnetic induction.

70
Generation of Electricity Through Magnetism
71
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72
Magnetism
  • This would be a very impractical method of
    generating electricity.
  • Electricity could also be generated by rotating a
    magnetic field around a stationary conductor or
    by rotating a conductor inside stationary
    magnetic field.

73
Magnetism
  • As the rotating conductor cuts across the lines
    of magnetism in the stationary magnetic field,
    electrons will be forced to flow through the
    conductor.

74
Magnetism
  • As the conductor continues to rotate, the
    conductor will travel parallel to the lines of
    magnetism and no electrons will flow.

75
Magnetism
  • As the conductor continues in its rotation, it
    will cut across the lines of magnetism in the
    opposite direction, causing the electrons in the
    conductor to flow in the opposite direction.
  • The cycle continues as the rotation continues.

76
Magnetism
  • In a commercial electricity generation power
    plant, a synchronous alternator is used to
    produce electricity.
  • This device has a rotating field winding and a
    stationary winding.

77
Magnetism
  • A small amount of electricity is supplied to the
    alternators field windings, which produces a
    magnetic field around the windings (the field
    windings become an electromagnet).

78
Magnetism
  • As the field windings are turned (by a turbine
    driven by an external power source), the magnetic
    field also turns, cutting across the alternators
    stationary windings.

79
Magnetism
  • Since the conductors are cutting across a
    magnetic field, electricity is induced into the
    stationary conductors.

80
Magnetism
  • Power plants may burn coal or use nuclear energy
    to make steam from heated water in order to turn
    the turbine, or they may use the kinetic energy
    of falling water to turn the turbine.

81
What is the difference between direct current and
alternating current and what are some
applications of each?
  • Objective 5

82
AC/DC
  • Electricity may be classified as direct current
    or alternating current depending on the pattern
    of flow of the electrons in the circuit.

83
Direct Current
  • In direct current or DC electricity, the
    electrons flow in only one direction.

84
Direct Current
  • Since electrons flow from the negative terminal
    to the positive terminal in an electrical
    circuit, sources of DC electricity must have a
    fixed polarity.

85
Direct Current
  • This means one specific terminal is always
    negative while the other is always positive.
  • Thermocouples and thermopiles, solar cells,
    batteries and fuel cells all produce DC
    electricity.

86
Direct Current
  • A DC generator may also be used to produce DC
    electricity through magnetism.

87
Alternating Current
  • With alternating current or AC, electricity flows
    first in one direction, stops, reverses and flows
    in the opposite direction.

88
Alternating Current
  • Once this occurs, the electricity is said to have
    completed one cycle.
  • AC electricity is the type generated by electric
    power plants and is what is used in homes,
    businesses, and other locations.

89
Alternating Current
  • One cycle of electrical flow is produced with
    each revolution of the plants synchronous
    alternator.
  • In the U.S., they turn at a speed of 60
    revolutions per second.
  • Therefore, current generated in the U.S.
    completes 60 cycles per second.

90
Alternating Current
  • The term hertz (Hz) represents one cycle per
    second, so in the U.S. our electricity is
    generated and delivered at 60 Hz.
  • In several other countries, 50 Hz AC electricity
    is the standard.

91
Review / Summary
  • 1. Relate electricity to the structure of
    elements and atoms.

92
Review / Summary
  • 2. Explain conductors, insulators, and
    semiconductors.

93
Review / Summary
  • 3. Explain the conventional and electron theories
    of electrical current flow.

94
Review / Summary
  • 4. Describe how electricity can be generated by
    friction, heat, light, chemical reactions, and
    magnetism.

95
Review / Summary
  • 5. Describe the difference between and
    applications of direct current (DC) and
    alternating current (AC) electricity.
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