lesson exploring the science of electricity. interest approach what is electricity? where does...

LessonLesson

Exploring the Science of Exploring the Science of ElectricityElectricity

Interest ApproachInterest Approach

What is Electricity?

Where does electricity come from?

How does it get from its source to where we use it?

Interest ApproachInterest Approach

What happens when you walk What happens when you walk across carpet in the winter and across carpet in the winter and receive a “shock” when you receive a “shock” when you touch someone or something touch someone or something metal?metal?

Interest Approach Interest Approach

Static electricity is actually a Static electricity is actually a transfer of electrons from you to transfer of electrons from you to the object you touchthe object you touch

Student Learning ObjectivesStudent Learning Objectives

Relate electricity to the structure Relate electricity to the structure of elements and atoms.of elements and atoms.

Explain conductors, insulators, Explain conductors, insulators, and semiconductors.and semiconductors.

Explain the conventional and Explain the conventional and electron theories of electrical electron theories of electrical current flow.current flow.

Student Learning ObjectivesStudent Learning Objectives

Describe how electricity can be Describe how electricity can be generated by friction, heat, light, generated by friction, heat, light, chemical reactions, and magnetism.chemical reactions, and magnetism.

Describe the difference between and Describe the difference between and applications of direct current (DC) applications of direct current (DC) and alternating current (AC) and alternating current (AC) electricity.electricity.

TermsTermso Alternating currentAlternating currento AtomsAtomso BatteryBatteryo ConductorsConductorso Conventional Conventional

theorytheoryo CycleCycleo Direct currentDirect currento ElectricityElectricityo ElectrodesElectrodes

oElectrolyteoElectromagnetoElectron theoryoElectronsoElementsoFree electronsoFrictionoFuel celloHertzoInsulators

TermsTerms

o Magnetic inductionMagnetic inductiono NeutronsNeutronso Photovoltaic effectPhotovoltaic effecto PolarityPolarityo Primary batteriesPrimary batterieso ProtonsProtonso Secondary Secondary

batteriesbatterieso SemiconductorsSemiconductors

oSolar (photo) celloSynchronous alternatoroThermocoupleoThermopileoValence

Objective 1:Objective 1:

How does electricity relate How does electricity relate to the structure to of to the structure to of elements and atoms?elements and atoms?

ElementsElements

Elements are substances that Elements are substances that cannot be broken down into simpler cannot be broken down into simpler substances using ordinary chemical substances using ordinary chemical methods. methods.

All matter is composed of one or All matter is composed of one or more elements. more elements.

AtomsAtoms

Atoms are the smallest units of an Atoms are the smallest units of an element. element.

They cannot be divided further They cannot be divided further without losing physical and without losing physical and chemical properties. chemical properties.

Atoms are composed of protons, Atoms are composed of protons, neutrons, and electrons.neutrons, and electrons.

Protons and NeutronsProtons and Neutrons

Protons have a positive Protons have a positive electrical charge, while electrical charge, while neutrons have no electrical neutrons have no electrical charge. charge.

Protons and NeutronsProtons and Neutrons

Protons and neutrons make up Protons and neutrons make up the nucleus, or center of each the nucleus, or center of each atom. atom.

Thus the nucleus of each atom Thus the nucleus of each atom has a positive electrical charge.has a positive electrical charge.

ElectronsElectrons

Electrons have a negative Electrons have a negative electrical charge and orbit the electrical charge and orbit the nucleus of an atom in rings or nucleus of an atom in rings or shells. shells.

Since unlike charges attract each Since unlike charges attract each other, the electrons are held in other, the electrons are held in orbit by the positively charged orbit by the positively charged nucleus. nucleus.

ElectronsElectrons

The outer ring of electrons is called The outer ring of electrons is called the valence ring. the valence ring.

Copper As A ConductorCopper As A Conductor

The element copper, has 29 The element copper, has 29 protons in its nucleus and 29 protons in its nucleus and 29 electrons which orbit its electrons which orbit its nucleus. nucleus.

The electrical charges cancel The electrical charges cancel each other. each other.

Artwork supplied with permission

of Interstate Publishers, Inc.

Copper as a ConductorCopper as a Conductor

The electrons actually orbit the The electrons actually orbit the nucleus in rings. nucleus in rings. –The first or inner ring can hold a maximum The first or inner ring can hold a maximum

of 2 electrons, the second ring, a of 2 electrons, the second ring, a maximum of 8 electrons, the third ring, a maximum of 8 electrons, the third ring, a maximum of 18, the fourth ring, a maximum of 18, the fourth ring, a maximum of 32, the fifth ring, a maximum maximum of 32, the fifth ring, a maximum of 50, and the sixth, a maximum of 72. of 50, and the sixth, a maximum of 72.


Generally, the rings closest to Generally, the rings closest to the nucleus are filled before the nucleus are filled before additional rings are started. additional rings are started.

Thus, copper has 1 electron in Thus, copper has 1 electron in the fourth ring or valence ring the fourth ring or valence ring (2 + 8 + 18 + 1).(2 + 8 + 18 + 1).


The number of electrons in The number of electrons in the valence ring has a key the valence ring has a key role in determining the role in determining the electrical characteristics of the electrical characteristics of the element.element.

Free Electrons moving between Free Electrons moving between copper atomscopper atoms

Artwork supplied with permission of Interstate Publishers, Inc.

What are conductors, insulators, and

semiconductors?


Conductors, Insulators, and Semiconductors

Conductors, insulators, and Conductors, insulators, and semiconductors are important in semiconductors are important in electricity and electronics. electricity and electronics.

The following will help explain The following will help explain each:each:

ConductorsConductors

Materials that allow electricity to Materials that allow electricity to flow through them easily. flow through them easily.

Copper, aluminum, silver, and Copper, aluminum, silver, and gold are good conductors. gold are good conductors.

ConductorsConductors

Generally, nearly all metals are Generally, nearly all metals are good electrical conductors. good electrical conductors.

Any element or material having Any element or material having atoms with three or fewer electrons atoms with three or fewer electrons in its valence ring will be a in its valence ring will be a conductor.conductor.

Insulators

Materials that do not allow Materials that do not allow electricity to flow through them electricity to flow through them under normal conditions. under normal conditions.

Materials such as rubber, plastic, Materials such as rubber, plastic, porcelain, and glass are all good porcelain, and glass are all good electrical insulators. electrical insulators.

Insulators

Any element or material Any element or material composed of atoms having five or composed of atoms having five or more electrons in the valence ring more electrons in the valence ring will be an insulator. will be an insulator.

Insulators are used to confine the Insulators are used to confine the flow of electricity to desired paths.flow of electricity to desired paths.

Semiconductors

Materials that are neither good Materials that are neither good conductors nor good insulators. conductors nor good insulators.

Semiconductors are manufactured Semiconductors are manufactured from elements having atoms with four from elements having atoms with four electrons in their valence rings. electrons in their valence rings.

Silicon and germanium are widely Silicon and germanium are widely used in making semi-conducting used in making semi-conducting materials.materials.


What are the conventional and What are the conventional and electron theories of electrical electron theories of electrical current flow?current flow?

Electricity

Electricity is the flow of electrons from atom to atom in a conductor.

There are two different theories to help describe electricity:

Conventional Theory

Says that electricity is the flow of Says that electricity is the flow of positively charged particles through a positively charged particles through a conductor. conductor.

This is the older theory and was This is the older theory and was developed before scientists discovered developed before scientists discovered the existence of electrons. the existence of electrons.

With this theory, it was assumed that With this theory, it was assumed that current flow in an electrical circuit was current flow in an electrical circuit was from positive to negative.from positive to negative.

The direction of current The direction of current flow according to theflow according to theconventional theory.conventional theory.

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Electron TheoryElectron Theory

This is the accepted model of This is the accepted model of electrical current flow, however, electrical current flow, however, because of tradition, the because of tradition, the conventional theory is still widely conventional theory is still widely used. used.

Either theory may be used as Either theory may be used as long as it is used consistently.long as it is used consistently.


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.


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.


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

The direction of current flow according to the

electron theory.

Artwork supplied with permissionof Interstate Publishers, Inc.


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.

How can electricity be generated How can electricity be generated by friction, heat, light, chemical by friction, heat, light, chemical

reactions, and magnetism?reactions, and magnetism?


An external force must be applied An external force must be applied to cause free electrons to flow to cause free electrons to flow through a conductor.through a conductor.

This force is the production or This force is the production or generation of electricity, which can generation of electricity, which can be generated in the following ways:be generated in the following ways:

How can electricity be generated by How can electricity be generated by friction, heat, light, chemical reactions, friction, heat, light, chemical reactions,

and magnetism?and magnetism?

Friction

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

Friction

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

FrictionFriction

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

FrictionFriction

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

FrictionFriction

When you touch someone else When you touch someone else or a doorknob, the excess or a doorknob, the excess electrons discharge through your electrons discharge through your hands resulting in a static hands resulting in a static electricity shock. electricity shock.

Friction is not a practical method Friction is not a practical method of generating electricity.of generating electricity.

ThermocoupleThermocouple

Heat or temperature differences Heat or temperature differences can be used to generate can be used to generate electricity using a thermocouple.electricity using a thermocouple.

A thermocouple consists of two A thermocouple consists of two dissimilar metals, such as iron dissimilar metals, such as iron and nickel, joined together to and nickel, joined together to form two junctions. form two junctions.


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


To increase output, several To increase output, several thermocouples are often combined thermocouples are often combined to form a device called a thermopile. to form a device called a thermopile.

These are often used in flame These are often used in flame detectors, furnace safety valves, detectors, furnace safety valves, and in precision heat measurement and in precision heat measurement devices.devices.

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.

Photovoltaic EffectPhotovoltaic 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.

Photovoltaic EffectPhotovoltaic EffectWhen 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.

ChemicalChemical

Reactions between certain Reactions between certain chemicals can be used to chemicals can be used to produce electricity. produce electricity.

ChemicalChemical

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.

ChemicalChemical

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

ChemicalChemical

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

ChemicalChemical

Each positive ion lost leaves Each positive ion lost leaves behind two electrons. behind two electrons.

Thus, the zinc plate soon takes Thus, the zinc plate soon takes on a negative charge. on a negative charge.

It then becomes the negative It then becomes the negative terminal of the cell. terminal of the cell.

ChemicalChemical

As the positive ions move As the positive ions move through the electrolyte, they through the electrolyte, they collide with the copper plate.collide with the copper plate.

The positive ions attract free The positive ions attract free electrons from the copper plate. electrons from the copper plate.

ChemicalChemical

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

ChemicalChemical

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

ChemicalChemical

This flow will continue until the This flow will continue until the difference in charge between the difference in charge between the two plates has dissipated. two plates has dissipated.

Once this happens, the cell will be Once this happens, the cell will be discharged. discharged.

ChemicalChemical

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

ChemicalChemical

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.

ChemicalChemical

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

Magnetism

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

MagnetismMagnetism

If a bar magnet is suspended freely If a bar magnet is suspended freely from a string, the magnet will turn from a string, the magnet will turn until one end points north and the until one end points north and the other end points south. other end points south.

The end pointing north is said to be The end pointing north is said to be the north pole of the magnet and the the north pole of the magnet and the end pointing south the south pole. end pointing south the south pole.

MagnetismMagnetism

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.

MagnetismMagnetism

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.

Generation of Electricity Through Magnetism

MagnetismMagnetism

This would be a very impractical This would be a very impractical method of generating electricity. method of generating electricity.

Electricity could also be generated Electricity could also be generated by rotating a magnetic field around by rotating a magnetic field around a stationary conductor or by a stationary conductor or by rotating a conductor inside rotating a conductor inside stationary magnetic field. stationary magnetic field.

MagnetismMagnetism

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

MagnetismMagnetism

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

MagnetismMagnetism

As the conductor continues in its As the conductor continues in its rotation, it will cut across the lines rotation, it will cut across the lines of magnetism in the opposite of magnetism in the opposite direction, causing the electrons in direction, causing the electrons in the conductor to flow in the the conductor to flow in the opposite direction. opposite direction.

The cycle continues as the rotation The cycle continues as the rotation continues. continues.

MagnetismMagnetism

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.

MagnetismMagnetism

A small amount of electricity is A small amount of electricity is supplied to the alternator’s field supplied to the alternator’s field windings, which produces a windings, which produces a magnetic field around the magnetic field around the windings (the field windings windings (the field windings become an electromagnet). become an electromagnet).

MagnetismMagnetism

As the field windings are turned As the field windings are turned (by a turbine driven by an (by a turbine driven by an external power source), the external power source), the magnetic field also turns, cutting magnetic field also turns, cutting across the alternator’s stationary across the alternator’s stationary windings. windings.

MagnetismMagnetism

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

MagnetismMagnetism

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

What is the difference between direct current and

alternating current and what are some applications of

each?

Objective 5:

AC/DCAC/DC

Electricity may be classified as direct current or alternating current depending on the pattern of flow of the electrons in the circuit.

Direct CurrentDirect Current

In direct current or DC electricity, In direct current or DC electricity, the electrons flow in only one the electrons flow in only one direction. direction.


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


This means one specific terminal This means one specific terminal is always negative while the is always negative while the other is always positive.other is always positive.

Thermocouples and thermopiles, Thermocouples and thermopiles, solar cells, batteries and fuel solar cells, batteries and fuel cells all produce DC electricity. cells all produce DC electricity.


A DC generator may also be A DC generator may also be used to produce DC electricity used to produce DC electricity through magnetism.through magnetism.

Alternating CurrentAlternating Current

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


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.


One cycle of electrical flow is produced with each revolution of the plant’s synchronous alternator. –In the U.S., they turn at a speed of 60 In the U.S., they turn at a speed of 60

revolutions per second. revolutions per second. –Therefore, current generated in the Therefore, current generated in the

U.S. completes 60 cycles per second. U.S. completes 60 cycles per second.


The term The term hertz hertz (Hz) represents (Hz) represents one cycle per second, so in the one cycle per second, so in the U.S. our electricity is generated U.S. our electricity is generated and delivered at 60 Hz. and delivered at 60 Hz.

In several other countries, 50 Hz In several other countries, 50 Hz AC electricity is the standard.AC electricity is the standard.

Review / SummaryReview / Summary

1. Relate electricity to the 1. Relate electricity to the structure of elements and atoms.structure of elements and atoms.


2. Explain conductors, insulators, 2. Explain conductors, insulators, and semiconductors.and semiconductors.


3. Explain the conventional and 3. Explain the conventional and electron theories of electrical electron theories of electrical current flow.current flow.


4. Describe how electricity can 4. Describe how electricity can be generated by friction, heat, be generated by friction, heat, light, chemical reactions, and light, chemical reactions, and magnetism.magnetism.


5. Describe the difference 5. Describe the difference between and applications of between and applications of direct current (DC) and direct current (DC) and alternating current (AC) alternating current (AC) electricity.electricity.

lesson exploring the science of electricity. interest approach what is electricity? where does...

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