€¦  · Web viewDescribe the origins and applications of magnetism. 1702 Describe the idea of a magnetic force. 1703 Describe the atomic structure for materials. 1704 Describe

COURSE TITLE: Fundamentals of Magnetism

DUTY TITLE: Electricity and Magnetism

POS #: 1700

TASK: Electricity and Magnetism

PURPOSE: To Understand the Principals of Magnetism & Electro-magnetism.

TASKS:

1701 Describe the origins and applications of magnetism.1702 Describe the idea of a magnetic force.1703 Describe the atomic structure for materials.1704 Describe the direction of electron flow in circuits.1705 List the effect of electric current flow.1706 Construct simple circuits.

NOTE: This task is not on the current Program of Study Task Listing; however this is an important theory the students must learn for the Electrical trade. The P.O.S. numbers shown are from a previous task listing. The entire world revolves around magnetism.

REVISION: 2019

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Schuylkill Technology Center-

South Campus15 Maple Avenue

Marlin, Pennsylvania 17951(570) 544-4748

RESIDENTIAL & INDUSTRIAL ELECTRICITY

Level 2Task 1700

Name:

Date:

Learning Guide Due Date:

Pre Test Due Date:

Post Test Due Date:

Total Hours: 20

Level(s): 2

ENGLISH LANGUAGE ARTSCC.1.2.11-12.J Acquire and use accurately general academic and domain-specific words and phrases, sufficient for reading, writing, speaking, and listening at the college and career readiness level; demonstrate independence in gathering vocabulary knowledge when considering a word or phrase important to comprehension or expressionCC.1.3.11-12.I Determine or clarify the meaning of unknown and multiple-meaning words and phrases based on grade level reading and content, choosing flexibly from a range of strategies and tools.CC.1.4.11-12.A Write informative/ explanatory texts to examine and convey complex ideas, concepts, and information clearly and accurately.

MATHCC.2.1.HS.F.4 Use units as a way to understand problems and to guide the solution of multi-step problems.CC.2.1.HS.F.6 Extend the knowledge of arithmetic operations and apply to complex numbers.

READING IN SCIENCE & TECHNOLOGYCC.3.5.11-12.B. Determine the central ideas or conclusions of a text; summarize complex concepts, processes, or information presented in a text by paraphrasing them in simpler but still accurate terms.CC.3.5.11-12.C. Follow precisely a complex multistep procedure when carrying out experiments, taking measurements, or performing technical tasks; analyze the specific results based on explanations in the text.

WRITING IN SCIENCE & TECHNOLOGYCC.3.6.11-12.E. Use technology, including the Internet, to produce, publish, and update individual or shared writing products in response to ongoing feedback, including new arguments or information.CC.3.6.11-12.F. Conduct short as well as more sustained research projects to answer a question (including a self generated question) or solve a problem; narrow or broaden the inquiry when appropriate; synthesize multiple sources on the subject, demonstrating understanding of the subject under investigationCC.3.6.11-12.H. Draw evidence from informational texts to support analysis, reflection, and research.

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*CORE CURRICULUM STANDARDS*

*ACADEMIC STANDARDS * READING, WRITING, SPEAKING & LISTENING

1.1.11.A Locate various texts, assigned for independent projects before reading.1.1.11.D Identify strategies that were most effective in learning1.1.11.E Establish a reading vocabulary by using new words1.1.11.F Understanding the meaning of, and apply key vocabulary across the various subject areas1.4.11.D Maintain a written record of activities1.6.11.A Listen to others, ask questions, and take notes

MATH2.2.11.A Develop and use computation concepts2.2.11.B Use estimation for problems that don’t need exact answers2.2.11.C Constructing and applying mathematical models2.2.11.D Describe and explain errors that may occur in estimates 2.2.11.E Recognize that the degree of precision need in calculating2.3.11.A Selecting and using the right units and tools to measure precise measurements2.5.11.A Using appropriate mathematical concepts for multi-step problems2.5.11.B Use symbols, terminology, mathematical rules, Etc.2.5.11.C Presenting mathematical procedures and results

SCIENCE3.1.12.A Apply concepts of systems, subsystems feedback and control to solve complex technological problems3.1.12.B Apply concepts of models as a method predict and understand science and technology3.1.12.C Assess and apply patterns in science and technology3.1.12D Analyze scale as a way of relating concepts and ideas to one another by some measure3.1.12.E Evaluate change in nature, physical systems and man-made systems3.2.12.A Evaluate the nature of scientific and technological knowledge3.2.12.B Evaluate experimental information for appropriateness3.2.12.C Apply elements of scientific inquiry to solve multi – step problems3.2.12.D Analyze the technological design process to solve problems3.4.12.A Apply concepts about the structure and properties of matter3.4.12.B Apply energy sources and conversions and their relationship to heat and temperature3.4.12.C Apply the principles of motion and force3.8.12.A Synthesize the interactions and constraints of science3.8.12.B Use of ingenuity and technological resources to solve specific societal needs and improve the quality of life3.8.12.C Evaluate the consequences and impacts of scientific and technological solutions

ECOLOGY STANDARDS4.2.10.A Explain that renewable and non-renewable resources supply energy and material.4.2.10.B Evaluate factors affecting availability of natural resources.4.2.10.C Analyze the use of renewable and non-renewable resources.

4.2.12.B Analyze factors affecting the availability of renewable and non-renewable resources.4.3.10.A Describe environmental health issues.4.3.10.B Explain how multiple variables determine the effects of pollution on environmental health, natural processes and human practices.4.3.12.C Analyze the need for a healthy environment.4.8.12.A Explain how technology has influenced the sustainability of natural resources over time.

CAREER & EDUCATION13.1.11.A Relate careers to individual interest, abilities, and aptitudes13.2.11.E Demonstrate in the career acquisition process the essential knowledge needed13.3.11.A Evaluate personal attitudes that support career advancement

ASSESSMENT ANCHORSM11.A.3.1.1 Simplify expressions using the order of operationsM11.A.2.1.3 Use proportional relationships in problem solving settingsM11.A.1.2 Apply any number theory concepts to show relationships between real numbers in problem solving

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*ACADEMIC STANDARDS*

STUDENTThe student will be able to understand the principals of magnetism, and the different effects of A.C. and D.C. voltages on a coil making an electro-magnet.

TERMINAL PERFORMANCE OBJECTIVEGiven all the electrical tools and materials required, the student will construct an A.C. and D.C. electromagnet and report on their findings to 100% accuracy and according to the teacher prepared checklist.

SAFETY Always wear safety glasses when working in the shop. Always check with the instructor before turning power on. Always use tools in the correct manner. Keep work area clean and free of debris. Never wire a project without the correct wiring diagram.

RELATED INFORMATION1. Attend lecture by instructor.2. Obtain handout.3. Review chapters in textbook.4. Define vocabulary words.5. Complete Pre Test (Prior Knowledge)6. Complete all questions in this packet.7. Complete test at the end of this packet. (This will be graded for accuracy!)8. Complete all projects in this packet.9. Complete Post Test (Post Knowledge)

10. Complete K-W-L Literacy Assignment by Picking an Article From the “Electrical Contractor” Magazine Located in the Theory Room. You can pick any article you feel is important to the electrical trade.

EQUIPMENT & SUPPLIES

1. Safety glasses 9. Magnets

2. Screw driver 10. Meters

3. Awl 11. Paper and pencil

4. Wire strippers 12. Metal filings

5. Side cutters 13. A.C & D.C. power supplies

6. Cable rippers 14. Coil of wire (Any gauge)

7. Lineman pliers

8. Needle nose pliers

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Magnetic Induction MagnInduction

Introduction

1. Magnetic induction is one of the most important concepts in the electrical field.

2. It is the basic operating principle for alternators, transformers, and AC motors.After studying this unit, the student should be able to:

1. Discuss magnetic induction.2. List factors that determine the amount and polarity of an induced voltage.3. Discuss Lenz’s law.4. Discuss an exponential curve.5. List devices used to help prevent induced voltage spikes.

CC.1.2.11-12.J Acquire and use accurately general academic and domain-specific words and phrases, sufficient for reading, writing, speaking, and listening at the college and career readiness level; demonstrate independence in gathering vocabulary knowledge when considering a word or phrase important to comprehension or expressionCC.1.3.11-12.I Determine or clarify the meaning of unknown and multiple-meaning words and phrases based on grade level reading and content, choosing flexibly from a range of strategies and tools.CC.1.4.11-12.A Write informative/ explanatory texts to examine and convey complex ideas, concepts, and information clearly and accurately.1.6.11A = Listen to others, ask questions, and take notes3.4.12.B = Apply energy sources and conversions and their relationship to heat and temperature

********FILL IN THE DEFINITIONS********

Eddy current:

Exponential curve:

Henry:

Hysteresis loss:

Magnetic induction:

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Lenz’s law: Metal oxide varistor (VAR):

R-L time constant:

Strength of magnetic field:

Turns of wire:

Voltage spike:

Weber:

Fleming’s Left-Hand Generator Rule:

Inductance:

Inductor:

Transformer:

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Permanent Magnet:

CC.1.2.11-12.J Acquire and use accurately general academic and domain-specific words and phrases, sufficient for reading, writing, speaking, and listening at the college and career readiness level; demonstrate independence in gathering vocabulary knowledge when considering a word or phrase important to comprehension or expression

CC.1.3.11-12.I Determine or clarify the meaning of unknown and multiple-meaning words and phrases based on grade level reading and content, choosing flexibly from a range of strategies and tools.CC.1.4.11-12.A Write informative/ explanatory texts to examine and convey complex ideas, concepts, and information clearly and accurately.1.6.11.A = Listen to others, ask questions and take note2.2.11.E = Recognize that the degree of precision need in calculating

Strength of magnetic field — the number of magnetic lines of flux per square inch of flux density of a magnetic field

Turns of wire — the number of turns of wire on a coil

Voltage spike — a large amount of voltage that exists for a very short period of time

Weber — a measure of magnetism equal to 100,000,000 lines of magnetic flux

A. Magnetic Induction1. Whenever current flows through a conductor, a magnetic field is created

around it

2. The direction of current flow determines the polarity of the magnetic field

3. The amount of current determines the strength of the magnetic field

4. The reverse of this is the principle of magnetic induction

5. Whenever a conductor cuts through magnetic lines of flux, a voltage is induced into the conductor

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6. When a conductor is moved through the magnetic lines of flux, the induced voltage causes the electrons to flow in one direction

7. If the conductor is moved in the opposite direction, the polarity of the induced voltage is reversed and the current will flow in the opposite direction

8. The polarity of the induced voltage is determined by the polarity of the magnetic field in relation to the direction of movement

B. Fleming’s Left-Hand Generator Rule

1. Used to determine the relationship of the motion of the conductor in a magnetic field to the direction of the induced current

2. Left hand thumb, forefinger, and center finger are placed at right angles to each other

3. Forefinger points in the direction of the field flux

4. Thumb points in the direction of thrust, or movement of the conductor

5. Center finger shows the direction of the current induced into the armature

6. THumb = Thrust

7. Forefinger = Force

8. Center finger = Current

C. Moving Magnetic Lines

1. Most AC generators or alternators work on the principle of the magnet moving while the conductor is stationary

2. Three factors determine the amount of voltage that will be induced in a conductor:

a. The number of turns of wireb. The strength of the magnetic fieldc. The speed of the cutting action

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3. One weber equals 100,000,000 lines of flux

4. To induce 1 volt in a conductor, the conductor must cut 1 weber in one second

5. As speed of rotation is increased, the amount of induced voltage is increased

6. As the strength of the magnetic field is increased, the amount of induced voltage is increased

7. If more turns of wire are added, the amount of induced voltage is increased

D. Lenz’s Law

1. 2. An induced voltage or current opposes the motion that causes it

2. Other laws concerning conductors have been developed from Lenz’s law

3. One is that inductors always oppose a change of current

E. Rise Time of Current in an Inductor

1. 2. According to Lenz’s law, induced voltage is opposite in polarity to the applied voltage

2. The induced voltage is proportional to the rate of the change of current, or the speed of the cutting action

F. The Exponential Curve

1. Is divided into five time constants and describes a rate of certain occurrences

2. Each time constraint is equal to 63.2% of some value Induced voltage is also known as the counter electromotive force, or counter-emf.

3. Because the current increases at a rate of 63.2% during each time constraint, it is theoretically impossible to reach the total current value

4. It will reach about 99.3% of total value and is considered to be complete

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G. Inductance

1. Measured in units called henrys (H) and represented by the letter “L”

2. A coil has an inductance of 1 henry when a current change of one amp per second results in an induced voltage of one volt

3. The amount of inductance in a coil is determined by its physical properties and construction

4. Air core inductor — a coil wound on a nonmagnetic core material such as wood or plastic

5. Iron core inductor — coil wound on a core made of magnetic material such as silicon steel or iron

6. Iron core inductors with fewer turns produce more inductance than air core inductors because of the good magnetic path of the core

7. Iron core inductors cannot be used in high frequency applications because of eddy current loss and hysteresis loss in the core material

8. How far windings are separated also determines inductancea. The farther apart the turns are, the less the inductance

9. Coil inductance can be determined by using: L = 0.4_ N2_A/Ia. Where:

1) L = inductance in henrys2) _ = 3.14163) N = number of turns of wire4) _ = permeability of the core material5) A = cross sectional area of the core6) I = length of the core

10. An inductor is basically an electromagnet that changes its polarity at regular intervals

11. The permeability of the core material is an important factor in inductors

12. Flux lines pass through materials with high permeability (silicon, steel, soft iron) better than through materials with low permeability (brass, copper, aluminum)

13. Once a core material has been saturated, the permeability value becomes approximately 1 and an increase in turns has only a small effect on the value of inductance.

H. R–L Time Constants

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1. The time necessary for the current in an inductor to reach its full Ohm’s law value

2. Computed using the formula T = L / Ra. Where:

T = time in seconds L = inductance in henrys R = resistance in ohms

I. Induced Voltage Spikes

1. Occurs when current flow through an inductor stops and the current decreases at an exponential rate

2. The spikes can be thousands of volts and cause serious damage to circuit components, especially solid state components

3. The induced voltage equals –L times the change in current divided by the change of time

4. A negative sign is placed in front of the L because the induced voltage is always opposite in polarity to the voltage that produces it

5. A device used to prevent voltage spikes when current stops flowing through an inductor is the diode

6. A diode is an electronic device that acts like an electrical check valve

7. Permits current flow in only one direction

8. Connected in parallel with the inductor so that when voltage is applied to the circuit, it is reverse biased and acts like an open switch

9. When the voltage is stopped, the induced voltage produced by the collapsing magnetic field will be in opposite polarity to the applied voltage

10. The diode then becomes forward biased and acts like a closed switch

11. Current now flows through the diode and completes the circuit back to the inductor

12. A silicon diode has a forward voltage drop of 0.7 volt regardless of the current flowing through it

13. Diodes can be used to eliminate induced voltage spikes in DC circuits only

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14. A metal oxide varistor (MOV) is a bidirectional device, which means that it will conduct current in either direction, allowing it to be used on AC circuits

15. Exhibits a change of resistance when the voltage reaches a certain point

16. MOV’s are extremely fast acting, typically can change resistance in less than 20 nanoseconds

17. Often found in surge protectors used to protect many home appliances and computers

18. If nothing is connected in the circuit with the inductor when the switch is opened, the induced voltage can be extremely high

19. The resistance of the circuit is the air gap between the switch contacts, which is practically infinite

20. The inductor will attempt to produce any voltage necessary to prevent a change of current

21. The induced voltage can reach thousands of volts

22. Operating principle of many high-voltage devices, such as automobile ignition systems

23. Another similar device is the electric fence charger

J. Summary

1. When current flows through a conductor, a magnetic field is created around the conductor

2. When a conductor is cut by a magnetic field, a voltage is induced in the conductor

3. The polarity of the induced voltage is determined by the polarity of the magnetic field in relation to the direction of motion

4. Three factors that determine the amount of induced voltage are:a. The number of turns of wireb. The strength of the magnetic fieldc. The speed of the cutting action

5. One volt is induced in a conductor when the magnetic lines of flux are cut at a rate of one weber per second

6. Induced voltage is always opposite in polarity to the applied voltage

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7. Inductors oppose a change of current

8. Current rises in an inductor at an exponential rate

9. An exponential curve is divided into five time constants

10. Each time constant is equal to 63.2% of some value

11. Inductance is measured in units called henrys (H)

12. A coil has an inductance of 1 henry when a current change of 1 amp per second results in an induced voltage of 1 volt

13. Air core inductors are wound on cores of nonmagnetic material

14. Iron core inductors are wound on cores of magnetic material

15. The amount of inductance an inductor will have is determined by the number of turns of wire and the physical construction of the coil

16. Inductors can produce extremely high voltages when the current flowing through them is stopped

17. Two devices used to help prevent large spike voltages are the resistor and the diode

********MAGNETISM PROJECTS******** CC.2.1.HS.F.4 Use units as a way to understand problems and to guide the solution of multi-step problems.CC.2.1.HS.F.6 Extend the knowledge of arithmetic operations and apply to complex numbers.CC.3.5.11-12.C. Follow precisely a complex multistep procedure when carrying out experiments, taking measurements, or performing technical tasks; analyze the specific results based on explanations in the text.

3.1.12.B = Applying concepts of models as a method predic 3.1.12.D = Analyze scale as a way of relating concepts and ideas to one another 3.2.12.A = Evaluate the nature of scientific and technological knowledge 3.2.12.B = Evaluate experimental information 3.2.12.C = Apply the elements of scientific inquiry to solve multi-step problems 3.4.12.C = Apply the principles of motion and force

PROJECT # 1

1. Using a large coil of wire, install coil onto an A.C. power supply.

2. Install a piece of paper and put the metal fillings on top of the coil.

3. Turn on power supply, USING A VERY LOW VOLTAGE, and record what happens to the metal fillings. (WATCH CURRENT!!!!!)

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4. Switch to a D.C. power supply and repeat steps 1-3.

5. Switch the polarity of the input power, repeat steps 1-3.

PROJECT # 2

1. Using only a 9 volt battery, a small amount of bell wire and a paper clip…construct an electromagnet that will pick up the paper clip.

2. Record your process and explain how this simple project works.

PROJECT # 3

1. See pages in this packet labeled (“MAGNETIC SUCTION”).

2. Complete the project and record your findings.

PROJECT # 4

1. Complete the 25 question test in this packet. This WILL be graded for accuracy and count as a PERFORMANCE grade.

CC.3.6.11-12.E. Use technology, including the Internet, to produce, publish, and update individual or shared writing products in response to ongoing feedback, including new arguments or information.CC.3.6.11-12.F. Conduct short as well as more sustained research projects to answer a question (including a self generated question) or solve a problem; narrow or broaden the inquiry when appropriate; synthesize multiple sources on the subject, demonstrating understanding of the subject under investigationCC.3.6.11-12.H. Draw evidence from informational texts to support analysis, reflection, and research.

IN YOUR OWN WORDS EXPLAIN HOW A TRANSFORMER OPERATES AND HOW THE FUNCTION IS RELATED TO MAGNETISM

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IN THE SPACE BELOW, USING A TEMPLATE, DRAW THE BASIC DIAGRAM OF A TRANSFORMER AND LABEL ALL THE PARTS OF THE

TRANSFORMER.

RECORD OF PROJECTS

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REFERENCE PAGES

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CC.3.5.11-12.B. Determine the central ideas or conclusions of a text; summarize complex concepts, processes, or information presented in a text by paraphrasing them in simpler but still accurate terms.

The Basis of Magnetism

The electrical basis for the magnetic properties of matter has been verified down to the atomic level. Because the electron has both an electric charge and a spin, it can be called a charge in motion. This charge in motion gives rise to a tiny magnetic field. In the case of many atoms, all the electrons are paired within energy levels, according to the exclusion principle, so that the electrons in each pair have opposite (antiparallel) spins and their magnetic fields cancel. In some atoms, however, there are more electrons with spins in one direction than in the other, resulting in a net magnetic field for the atom as a whole; this situation exists in a paramagnetic substance. If such a material is placed in an external field, e.g., the field created by an electromagnet, the individual atoms will tend to align their fields with the external one. The alignment will not be complete, due to the disruptive effect of thermal vibrations. Because of this, a paramagnetic substance is only weakly attracted by a magnet.

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In a ferromagnetic substance, there are also more electrons with spins in one direction than in the other. The individual magnetic fields of the atoms in a given region tend to line up in the same direction, so that they reinforce one another. Such a region is called a domain. In an unmagnetized sample, the domains are of different sizes and have different orientations. When an external magnetic field is applied, domains whose orientations are in the same general direction as the external field will grow at the expense of domains with other orientations. When the domains in all other directions have vanished, the remaining domains are rotated so that their direction is exactly the same as that of the external field. After this rotation is complete, no further magnetization can take place, no matter how strong the external field; a saturation point is said to have been reached. If the external field is then reduced to zero, it is found that the sample still retains some of its magnetism; this is known as hysteresis.

Currents from magnetism A further connection between electricity and magnetism was discovered by Faraday, who found that changing magnetic fields though loops of wire will cause currents to be induced. For example, consider the wire loop below, and imagine a bar magnet is brought into the vicinity.

  Figure 9.16: Wire loop

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If a magnetic field is pushed into the plane of this loop, a counterclockwise current will be induced, as indicated. Alternatively, if the magnetic field is pulled out of the loop, a clockwise current will be induced. These induced currents only exist as long as the magnet is moving, and will die off when the magnet becomes stationary. These induced currents have an interesting aspect as far as there magnetic properties are concerned. Recall from the last section that currents induce magnetic fields. Thus, by either pushing or pulling the magnet into or out of the wire loop, one is inducing magnetic fields within this loop. The direction of these induced magnetic fields are such that if one is externally increasing the magnetic field through the loop by pushing a magnet in, then the induced field will be such as to decrease the magnetic field through the loop; this is indicated in the previous figure. Alternatively, if one is externally decreasing the magnetic field through the loop by pulling a magnet out, then the induced field will be such as to increase the magnetic field through the loop. This feature that the magnetic effects of the induced current are such as to oppose the external change is known as Lenz's law.

The induction of currents from changing magnetic fields has a number of important applications, some of which we now discuss.

Electricity is the flow of electrical power or charge. It is a secondary energy source which means that we get it from the conversion of other sources of energy, like coal, natural gas, oil, nuclear power and other natural sources, which are called primary sources. The energy sources we use to make electricity can be renewable or non-renewable, but electricity itself is neither renewable nor non-renewable.

Electricity is a basic part of nature and it is one of our most widely used forms of energy. Many cities and towns were built alongside waterfalls (a primary source of mechanical energy) that turned water wheels to perform work. Before electricity generation began slightly over 100 years ago, houses were lit with kerosene lamps, food

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was cooled in iceboxes, and rooms were warmed by wood-burning or coal-burning stoves. Beginning with Benjamin Franklin's experiment with a kite one stormy night in Philadelphia, the principles of electricity gradually became understood. Thomas Edison helped change everyone's life -- he perfected his invention -- the electric light bulb. Prior to 1879, direct current (DC) electricity had been used in arc lights for outdoor lighting. In the late-1800s, Nikola Tesla pioneered the generation, transmission, and use of alternating current (AC) electricity, which can be transmitted over much greater distances than direct current. Tesla's inventions used electricity to bring indoor lighting to our homes and to power industrial machines.

Despite its great importance in our daily lives, most of us rarely stop to think what life would be like without electricity. Yet like air and water, we tend to take electricity for granted. Everyday, we use electricity to do many jobs for us -- from lighting and heating/cooling our homes, to powering our televisions and computers.  Electricity is a controllable and convenient form of energy used in the applications of heat, light and power. 

THE SCIENCE OF ELECTRICITY developed by the National Energy Education Development Project

In order to understand how electric charge moves from one atom to another, we need to know something about atoms. Everything in the universe is made of atoms—every star, every tree, every animal. The human body is made of atoms. Air and water are, too. Atoms are the building blocks of the universe. Atoms are so small that millions of them would fit on the head of a pin.

Atoms are made of even smaller particles. The center of an atom is called the nucleus. It is made of particles called protons and neutrons. The protons and neutrons are very small, but electrons are much, much smaller. Electrons spin around the nucleus in shells a great distance from the nucleus. If the nucleus were the size of a tennis ball, the atom would be the size of the Empire State Building. Atoms are mostly empty space.

If you could see an atom, it would look a little like a tiny center of balls surrounded by giant invisible bubbles (or shells). The electrons would be on the surface of the bubbles, constantly spinning and moving to stay as far away from each other as possible. Electrons are held in their shells by an electrical force.

The protons and electrons of an atom are attracted to each other. They both carry an electrical charge. An electrical charge is a force within the particle. Protons have a positive charge (+) and electrons have a negative charge (-). The positive charge of the protons is equal to the negative charge of the electrons. Opposite charges attract each other. When an atom is in balance, it has an equal number of protons and electrons. The neutrons carry no charge and their number can vary.

The number of protons in an atom determines the kind of atom, or element, it is. An element is a substance in which all of the atoms are identical (the Periodic Table shows all the known elements). Every atom of hydrogen, for example, has one proton and one

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electron, with no neutrons. Every atom of carbon has six protons, six electrons, and six neutrons. The number of protons determines which element it is.

Electrons usually remain a constant distance from the nucleus in precise shells. The shell closest to the nucleus can hold two electrons. The next shell can hold up to eight. The outer shells cans hold even more. Some atoms with many protons can have as many as seven shells with electrons in them.

The electrons in the shells closest to the nucleus have a strong force of attraction to the protons. Sometimes, the electrons in the outermost shells do not. These electrons can be pushed out of their orbits. Applying a force can make them move from one atom to another. These moving electrons are electricity.

STATIC ELECTRICITYElectricity has been moving in the world forever. Lightning is a form of electricity. It is electrons moving from one cloud to another or jumping from a cloud to the ground. Have you ever felt a shock when you touched an object after walking across a carpet? A stream of electrons jumped to you from that object. This is called static electricity.

Have you ever made your hair stand straight up by rubbing a balloon on it? If so, you rubbed some electrons off the balloon. The electrons moved into your hair from the balloon. They tried to get far away from each other by moving to the ends of your hair.

They pushed against each other and made your hair move—they repelled each other. Just as opposite charges attract each other, like charges repel each other.

MAGNETS AND ELECTRICITY In most objects, all of the forces are in balance. Half of the electrons are spinning in one direction; half are spinning in the other. These spinning electrons are scattered evenly throughout the object.

Magnets are different. In magnets, most of the electrons at one end are spinning in one direction. Most of the electrons at the other end are spinning in the opposite direction.

Bar MagnetThis creates an imbalance in the forces between the ends of a magnet. This creates a magnetic field around a magnet. A magnet is labeled with North (N) and South (S) poles. The magnetic force in a magnet flows from the North pole to the South pole.

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Have you ever held two magnets close to each other? They don’t act like most objects. If you try to push the South poles together, they repel each other. Two North poles also repel each other.

Turn one magnet around and the North (N) and the South (S) poles are attracted to each other. The magnets come together with a strong force. Just like protons and electrons, opposites attract.

These special properties of magnets can be used to make electricity. Moving magnetic fields can pull and push electrons. Some metals, like copper have electrons that are loosely held. They can be pushed from their shells by moving magnets. Magnets and wire are used together in electric generators.

BATTERIES PRODUCE ELECTRICITYA battery produces electricity using two different metals in a chemical solution. A chemical reaction between the metals and the chemicals frees more electrons in one metal than in the other. One end of the battery is attached to one of the metals; the other end is attached to the other metal. The end that frees more electrons develops a positive charge and the other end develops a negative charge. If a wire is attached from one end of the battery to the other, electrons flow through the wire to balance the electrical charge. A load is a device that does work or performs a job. If a load––such as a light bulb––is placed along the wire, the electricity can do work as it flows through the wire. In the picture above, electrons flow from the negative end of the

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battery through the wire to the light bulb. The electricity flows through the wire in the light bulb and back to the battery.

ELECTRICITY TRAVELS IN CIRCUITSElectricity travels in closed loops, or circuits (from the word circle). It must have a complete path before the electrons can move. If a circuit is open, the electrons cannot flow. When we flip on a light switch, we close a circuit. The electricity flows from the electric wire through the light and back into the wire. When we flip the switch off, we open the circuit. No electricity flows to the light. When we turn a light switch on, electricity flows through a tiny wire in the bulb. The wire gets very hot. It makes the gas in the bulb glow. When the bulb burns out, the tiny wire has broken. The path through the bulb is gone. When we turn on the TV, electricity flows through wires inside the set, producing pictures and sound. Sometimes electricity runs motors—in washers or mixers. Electricity does a lot of work for us. We use it many times each day.

HOW ELECTRICITY IS GENERATEDAn electric generator is a device for converting mechanical energy into electrical energy.  The process is based on the relationship between magnetism and electricity. When a wire or any other electrically conductive material moves across a magnetic field, an electric current occurs in the wire. The large generators used by the electric utility industry have a stationary conductor. A magnet attached to the end of a rotating shaft is positioned inside a stationary conducting ring that is wrapped with a long, continuous piece of wire. When the magnet rotates, it induces a small electric current in each section of wire as it passes. Each section of wire constitutes a small, separate electric conductor. All the small currents of individual sections add up to one current of considerable size. This current is what is used for electric power.

An electric utility power station uses a turbine, engine, water wheel, or other similar machine to drive an electric generator or a device that converts mechanical or chemical

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energy to generate electricity. Steam turbines, internal-combustion engines, gas combustion turbines, water turbines, and wind turbines are the most common methods to generate electricity.  Most power plants are about 35 percent efficient. That means that for every 100 units of energy that go into a plant, only 35 units are converted to usable electrical energy.

Most of the electricity in the United States is produced in steam turbines. A turbine converts the kinetic energy of a moving fluid (liquid or gas) to mechanical energy. Steam turbines have a series of blades mounted on a shaft against which steam is forced, thus rotating the shaft connected to the generator. In a fossil-fueled steam turbine, the fuel is burned in a furnace to heat water in a boiler to produce steam.

Coal, petroleum (oil), and natural gas are burned in large furnaces to heat water to make steam that in turn pushes on the blades of a turbine. Did you know that coal is the largest single primary source of energy used to generate electricity in the United States? In 2003, more than half (51%) of the country's 3.9 trillion kilowatt-hours of electricity used coal as its source of energy.

Natural gas, in addition to being burned to heat water for steam, can also be burned to produce hot combustion gases that pass directly through a turbine, spinning the blades of the turbine to generate electricity. Gas turbines are commonly used when electricity utility usage is in high demand. In 2003, 16% of the nation's electricity was fueled by natural gas.

Petroleum can also be used to make steam to turn a turbine. Residual fuel oil, a product refined from crude oil, is often the petroleum product used in electric plants that use petroleum to make steam. Petroleum was used to generate about three percent (3%) of all electricity generated in U.S. electricity plants in 2003.

Nuclear power is a method in which steam is produced by heating water through a process called nuclear fission. In a nuclear power plant, a reactor contains a core of nuclear fuel, primarily enriched uranium. When atoms of uranium fuel are hit by neutrons they fission (split), releasing heat and more neutrons. Under controlled conditions, these other neutrons can strike more uranium atoms, splitting more atoms, and so on. Thereby, continuous fission can take place, forming a chain reaction releasing heat. The heat is used to turn water into steam that, in turn, spins a turbine that generates electricity. Nuclear power was used to generate 20% of all the country's electricity in 2003.

Hydropower, the source for almost 7% of U.S. electricity generation in 2003, is a process in which flowing water is used to spin a turbine connected to a generator. There are two basic types of hydroelectric systems that produce electricity. In the first system, flowing water accumulates in reservoirs created by the use of dams. The water falls through a pipe called a penstock and applies pressure against the turbine blades to drive the generator to produce electricity. In the second system, called run-of-river, the force of the river current (rather than falling water) applies pressure to the turbine blades to produce electricity.

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Geothermal power comes from heat energy buried beneath the surface of the earth. In some areas of the country, enough heat rises close to the surface of the earth to heat underground water into steam, which can be tapped for use at steam-turbine plants. This energy source generated less than 1% of the electricity in the country in 2003.

Solar power is derived from the energy of the sun.  However, the sun's energy is not available full-time and it is widely scattered. The processes used to produce electricity using the sun's energy have historically been more expensive than using conventional fossil fuels. Photovoltaic conversion generates electric power directly from the light of the sun in a photovoltaic (solar) cell. Solar-thermal electric generators use the radiant energy from the sun to produce steam to drive turbines. In 2003, less than 1% of the nation's electricity was based on solar power.

Wind power is derived from the conversion of the energy contained in wind into electricity. Wind power, less than 1% of the nation's electricity in 2003, is a rapidly growing source of electricity. A wind turbine is similar to a typical wind mill.

Biomass includes wood, municipal solid waste (garbage), and agricultural waste, such as corn cobs and wheat straw. These are some other energy sources for producing electricity. These sources replace fossil fuels in the boiler. The combustion of wood and waste creates steam that is typically used in conventional steam-electric plants. Biomass accounts for about 2% of the electricity generated in the United States.

THE TRANSFORMER - MOVING ELECTRICITY To solve the problem of sending electricity over long distances, George Westinghouse developed a device called a transformer. The transformer allowed electricity to be efficiently transmitted over long distances. This made it possible to supply electricity to homes and businesses located far from the electric generating plant.

The electricity produced by a generator travels along cables to a transformer, which changes electricity from low voltage to high voltage. Electricity can be moved long distances more efficiently using high voltage. Transmission lines are used to carry the electricity to a substation. Substations have transformers that change the high voltage electricity into lower voltage electricity. From the substation, distribution lines carry the electricity to homes, offices and factories, which require low voltage electricity.

MEASURING ELECTRICITYElectricity is measured in units of power called watts. It was named to honor James Watt, the inventor of the steam engine. One watt is a very small amount of power. It would require nearly 750 watts to equal one horsepower. A kilowatt represents 1,000 watts. A

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kilowatt-hour (kWh) is equal to the energy of 1,000 watts working for one hour. The amount of electricity a power plant generates or a customer uses over a period of time is measured in kilowatt-hours (kWh). Kilowatt-hours are determined by multiplying the number of kW required by the number of hours of use. For example, if you use a 40-watt light bulb 5 hours a day, you have used 200 watts of power, or 0.2 kilowatt-hours of electrical energy.

Sources: Energy Information Administration, Energy INFO card.The National Energy Education Development Project, Intermediate Energy.

Evolution of Electromagnetic TheoryThe connections between magnetism and electricity were discovered in the early part of the 19th cent. In 1820 H. C. Oersted found that a wire carrying an electrical current deflects the needle of a magnetic compass because a magnetic field is created by the moving electric charges constituting the current. It was found that the lines of induction of the magnetic field surrounding the wire (or any other conductor) are circular. If the wire is bent into a coil, called a solenoid, the magnetic fields of the individual loops combine to produce a strong field through the core of the coil. This field can be increased manyfold by inserting a piece of soft iron or other ferromagnetic material into the core; the resulting arrangement constitutes an electromagnet.

Following Oersted's discovery the various magnetic effects of an electric current were extensively investigated by J. B. Biot, Félix Savart, and A. M. Ampère. Ampère showed in 1825 that not only does a current-carrying conductor exert a force on a magnet but magnets also exert forces on current-carrying conductors. In 1831 Michael Faraday and Joseph Henry independently discovered that it is possible to produce a current in a conductor by changing the magnetic field about it. The discovery of this effect, called electromagnetic induction, together with the discovery that an electric current produces a magnetic field, laid the foundation for the modern age of electricity. Both the electric generator, which makes electricity widely available, and the electric motor, which converts electricity to useful mechanical work, are based on these effects.

Another relationship between electricity and magnetism is that a regularly changing electric current in a conductor will create a changing magnetic field in the space about the conductor, which in turn gives rise to a changing electrical field. In this way regularly oscillating electric and magnetic fields can generate each other. These fields can be visualized as a single wave that is propagating through space. The formal theory underlying this electromagnetic radiation was developed by James Clerk Maxwell in the middle of the 19th cent. Maxwell showed that the speed of propagation of electromagnetic radiation is identical with that of light, thus revealing that light is intimately connected with electricity and magnetism.

Force on a current-carrying wire

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It follows from the fact that moving charges experience a force in a magnetic field that a current-carrying wire will also experience such a force, since a current consists of moving charges. An illustration of this effect appears below.

  Figure 9.7: Force on a current-carrying

wire in a magnetic field

This property is at the heart of a number of devices, which we now discuss.

Magnetic forces on moving charges One basic feature of magnetism is that, in the vicinity of a magnetic field, a moving charge will experience a force. Interestingly, the force on the charged particle is always perpendicular to the direction it is moving. Thus magnetic forces cause charged particles to change their direction of motion, but they do not change the speed of the particle. This property is used in high-energy particle accelerators to focus beams of particles which eventually collide with targets to produce new particles. Another way to understand this is to realize that if the force is perpendicular to the motion, then no work is done. Hence magnetic forces do no work on charged particles and cannot increase their kinetic energy. If a charged particle moves through a constant magnetic field, its speed stays the same, but its direction is constantly changing. A device in which this property is used is the mass spectrometer, which is used to identify elements. A basic mass spectrometer is pictured below.

Figure 9.6: Mass spectrometer

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In this device a beam of charged particles (ions) enter a region of a magnetic field, where they experience a force and are bent in a circular path. The amount of bending depends on the mass (and charge) of the particle, and by measuring this amount one can infer they type of particle that is present by comparing to the bending of known elements

Magnetic MaterialsThe term magnetism is derived from Magnesia, the name of a region in Asia Minor where lodestone, a naturally magnetic iron ore, was found in ancient times. Iron is not the only material that is easily magnetized when placed in a magnetic field; others include nickel and cobalt. Carbon steel was long the material commonly used for permanent magnets, but more recently other materials have been developed that are much more efficient as permanent magnets, including certain ferroceramics and Alnico, an alloy containing iron, aluminum, nickel, cobalt, and copper.

Materials that respond strongly to a magnetic field are called ferromagnetic [Lat. ferrum = iron]. The ability of a material to be magnetized or to strengthen the magnetic field in its vicinity is expressed by its magnetic permeability. Ferromagnetic materials have permeabilities of as much as 1,000 or more times that of free space (a vacuum). A number of materials are very weakly attracted by a magnetic field, having permeabilities slightly greater than that of free space; these materials are called paramagnetic. A few materials, such as bismuth and antimony, are repelled by a magnetic field, having permeabilities less than that of free space; these materials are called diamagnetic.

Magnetic Poles, Forces, and FieldsAny object that exhibits magnetic properties is called a magnet. Every magnet has two points, or poles, where most of its strength is concentrated; these are designated as a

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north-seeking pole, or north pole, and a south-seeking pole, or south pole, because a suspended magnet tends to orient itself along a north-south line. Since a magnet has two poles, it is sometimes called a magnetic dipole, being analogous to an electric dipole, composed of two opposite charges. The like poles of different magnets repel each other, and the unlike poles attract each other.

One remarkable property of magnets is that whenever a magnet is broken, a north pole will appear at one of the broken faces and a south pole at the other, such that each piece has its own north and south poles. It is impossible to isolate a single magnetic pole, regardless of how many times a magnet is broken or how small the fragments become. (The theoretical question as to the possible existence in any state of a single magnetic pole, called a monopole, is still considered open by physicists; experiments to date have failed to detect one.)

From his study of magnetism, C. A. Coulomb in the 18th cent. found that the magnetic forces between two poles followed an inverse-square law of the same form as that describing the forces between electric charges. The law states that the force of attraction or repulsion between two magnetic poles is directly proportional to the product of the strengths of the poles and inversely proportional to the square of the distance between them.

As with electric charges, the effect of this magnetic force acting at a distance is expressed in terms of a field of force. A magnetic pole sets up a field in the space around it that exerts a force on magnetic materials. The field can be visualized in terms of lines of induction (similar to the lines of force of an electric field). These imaginary lines indicate the direction of the field in a given region. By convention they originate at the north pole of a magnet and form loops that end at the south pole either of the same magnet or of some other nearby magnet (see also flux, magnetic). The lines are spaced so that the number per unit area is proportional to the field strength in a given area. Thus, the lines converge near the poles, where the field is strong, and spread out as their distance from the poles increases.

A picture of these lines of induction can be made by sprinkling iron filings on a piece of paper placed over a magnet. The individual pieces of iron become magnetized by entering a magnetic field, i.e., they act like tiny magnets, lining themselves up along the lines of induction. By using variously shaped magnets and various combinations of more than one magnet, representations of the field in these different situations can be obtained.

Magnetic Suction

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This experiment shows how your doorbell works.

     A coil of wire with current flowing through it forms an electromagnet that acts very much like a bar magnet. The coil will magnetize an iron nail and attract it in a remarkably vigorous way.

  40 feet (12 m) of insulated bell wire.

  A plastic or cardboard tube 4 to 6 inches (10 to 15 cm) long and about 1/4 inch (6 mm) in diameter.

  A large battery, 6 volts or more. (An ordinary 1.5-volt D battery will work, but may go dead very quickly and will require more coils to get the same effect.)

  The largest iron nail that will fit in the tube loosely.

Tightly wrap as many coils of wire as possible around the tube, leaving the two ends free so that you can strip the insulation off them and connect them to a battery.

Insert the nail part of the way into the coil and briefly connect the ends of the wires to the

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battery. (Leaving the wires connected too long will result in death for your battery and perhaps a burn for you from the hot wires.) The nail should be sucked into the coil. Reverse the leads to the battery and repeat the experiment, after predicting what will happen.

Any moving electric charge creates a magnetic field around it. A loop of wire with a current creates a magnetic field through the loop. You can increase the strength of this field by piling up a lot of loops. The more

loops, the stronger the magnet. Like a bar magnet, this coil of wire now has a north pole and a south pole.

Because of the motion of electrons around its nucleus, each iron atom can be thought of as a tiny loop of moving charge. Each atom therefore acts like a small magnet. Ordinarily, all these "loops" point in different directions, so the iron has no overall magnetism. But suppose you bring a nail near the south pole of your electromagnet. The north poles of the iron atoms will be attracted to the south pole of the electromagnet and will all line up pointing in the same direction. The nail is now magnetized, with its north poles facing the south pole of the electromagnet. The opposite poles attract each other, and the nail is sucked into the electromagnet.

When the direction of current is reversed, the poles of the electromagnet reverse. Knowing this, you might think that when you bring the nail near the same end of the electromagnet as you did previously, the nail would now be repelled by the electromagnet, rather than attracted and sucked into it again. But when you try it, the nail does the same thing it did before. That's because the nail's iron atoms all reorient so that they line up with their opposite poles pointing toward whatever pole the electromagnet presents. Thus the nail will always be attracted to the electromagnet and will never be repelled. You can find which end of the coil is the magnetic north pole by wrapping the fingers of your right hand around the coil in the direction the current is flowing; your thumb will point to the north end of the coil. You can also use a magnetic compass.

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The principle of magnetic suction is used to make a variety of devices, from doorbells (in which an iron rod is sucked into a coil to strike a chime) to pinball machines (in which current goes through a coil, sucking in a rod that is attached to the flipper) to the starter switch on your car.

To extend the original activity, hold the coil vertically and repeat the experiment. Try smaller nails and straightened paper clips in the coil Remove the nail from the coil and test its magnetic properties by seeing if you can pick up some paper clips with it. If the electromagnet is not strong enough, the nail will not stay magnetized after the battery is disconnected, so to see this effect use as large a current source as possible. If the electromagnet is strong enough, the nail may stay magnetized for a while, until the random jiggling of the iron atoms eventually moves them out of alignment again. To demagnetize the nail rapidly, drop it onto a solid surface, such as a cement floor, a couple of times. This knocks the iron atoms out of alignment. Try to pick up paper clips with the demagnetized nail.

Magnetismby Ron Kurtus (revised 6 October 2006)

Magnetism is a force that acts at a distance due to a magnetic field. This field is caused by moving electrically charged particles or is inherent in magnetic objects such as a magnet. A magnet is an object that exhibits a strong magnetic field and will attract materials like iron to it. Magnets have two poles, called the north (N) and south (S) poles. Two magnets will be attracted by their opposite poles, and each will repel the like pole of the other magnet. Magnetism has many uses in modern life.

Questions you may have include:

What is a magnetic field?

What are magnets?

How is magnetism used?

This lesson will answer those questions. There is a mini-quiz near the end of the lesson.

Magnetic fieldA magnetic field consists of imaginary lines of flux coming from moving or spinning electrically charged particles. Examples include the spin of a proton and the motion of electrons through a wire in an electric circuit.

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What a magnetic field actually consists of is somewhat of a mystery, but we do know it is a special property of space.

Magnetic field or lines of flux of a moving charged particle

Names of polesThe lines of magnetic flux flow from one end of the object to the other. By convention, we call one end of a magnetic object the N or North-seeking pole and the other the S or South-seeking pole, as related to the Earth's North and South magnetic poles. The magnetic flux is defined as moving from N to S.

MagnetsAlthough individual particles such as electrons can have magnetic fields, larger objects such as a piece of iron can also have a magnetic field, as a sum of the fields of its particles. If a larger object exhibits a sufficiently great magnetic field, it is called a magnet.

Magnetic forceThe magnetic field of an object can create a magnetic force on other objects with magnetic fields. That force is what we call magnetism.

When a magnetic field is applied to a moving electric charge, such as a moving proton or the electrical current in a wire, the force on the charge is called a Lorentz force.

AttractionWhen two magnets or magnetic objects are close to each other, there is a force that attracts the poles together.

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Force attracts N to S

Magnets also strongly attract ferromagnetic materials such as iron, nickel and cobalt.

RepulsionWhen two magnetic objects have like poles facing each other, the magnetic force pushes them apart.

Force pushes magnetic objects apart

Magnets can also weakly repel diamagnetic materials. (See Magnetic Materials for more information.)

Magnetic and electric fieldsThe magnetic and electric fields are both similar and different. They are also inter-related.

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Electric charges and magnetism similarJust as the positive (+) and negative (-) electrical charges attract each other, the N and S poles of a magnet attract each other.

In electricity like charges repel, and in magnetism like poles repel.

Electric charges and magnetism differentThe magnetic field is a dipole field. That means that every magnet must have two poles.

On the other hand, a positive (+) or negative (-) electrical charge can stand alone. Electrical charges are called monopoles, since they can exist without the opposite charge.

In conclusionMagnetism is a force that acts at a distance and is caused by a magnetic field. The magnetic force strongly attracts an opposite pole of another magnet and repels a like pole. The magnetic field is both similar and different than an electric field.

Magnetism    The ancient Greeks, originally those near the city of Magnesia, and also the early Chinese knew about strange and rare stones (possibly chunks of iron ore struck by lightning) with the power to attract iron. A steel needle stroked with such a "lodestone" became "magnetic" as well, and around 1000 the Chinese found that such a needle, when freely suspended, pointed north-south.     The magnetic compass soon spread to Europe. Columbus used it when he crossed the Atlantic ocean, noting not only that the needle deviated slightly from exact north (as indicated by the stars) but also that the deviation changed during the voyage. Around 1600 William Gilbert, physician to Queen Elizabeth I of England, proposed an explanation: the Earth itself was a giant magnet, with its magnetic poles some distance away from its geographic ones (i.e. near the points defining the axis around which the Earth turns).

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The Magnetosphere

    On Earth one needs a sensitive needle to detect magnetic forces, and out in space they are usually much, much weaker. But beyond the dense atmosphere, such forces have a much bigger role, and a region exists around the Earth where they dominate the environment, a region known as the Earth's magnetosphere. That region contains a mix of electrically charged particles, and electric and magnetic phenomena rather than gravity determine its structure. We call it the Earth's magnetosphere

    Only a few of the phenomena observed on the ground come from the magnetosphere: fluctuations of the magnetic field known as magnetic storms and sub storms, and the polar aurora or "northern lights," appearing in the night skies of places like Alaska and Norway. Satellites in space, however, sense much more: radiation belts, magnetic structures, fast streaming particles and processes which energize them. All these are described in the sections that follow.

But what is magnetism?    Until 1821, only one kind of magnetism was known, the one produced by iron magnets. Then a Danish scientist, Hans Christian Oersted, while demonstrating to friends the flow of an electric current in a wire, noticed that the current caused a nearby compass needle to move. The new phenomenon was studied in France by Andre-Marie Ampere, who concluded that the nature of magnetism was quite different from what everyone had believed. It was basically a force between electric currents: two parallel currents in the same direction attract, in opposite directions repel. Iron magnets are a very special case, which Ampere was also able to explain.

What Oersted saw...

    In nature, magnetic fields are produced in the rarefied gas of space, in the glowing heat of sunspots and in the molten core of the Earth. Such magnetism must be produced by electric

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currents, but finding how those currents are produced remains a major challenge.

Magnetic Field Lines    Michael Faraday, credited with fundamental discoveries on electricity and magnetism (an electric unit is named "Farad" in his honor), also proposed a widely used method for visualizing magnetic fields. Imagine a compass needle freely suspended in three dimensions, near a magnet or an electrical current. We can trace in space (in our imagination, at least!) the lines one obtains when one "follows the direction of the compass needle." Faraday called them lines of force, but the term field lines is now in common use.

Compass needles outlining field lines

Field lines of a bar magnet are commonly illustrated by iron filings sprinkled on a sheet of paper held over a magnet. Similarly, field lines of the Earth start near the south pole of the Earth, curve around in space and converge again near the north pole.

    However, in the Earth's magnetosphere, currents also flow through space and modify this pattern: on the side facing the Sun, field lines are compressed earthward, while on the night side they are pulled out into a very long "tail," like that of a comet. Near Earth, however, the lines remain very close to the "dipole pattern" of a bar magnet, so named because of its two poles.

Magnetic field lines from an idealized model.    To Faraday field lines were mainly a method of displaying the structure of the magnetic force. In space research, however, they have a much broader significance, because electrons and ions tend to stay attached to them, like beads on a wire, even becoming trapped when

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conditions are right. Because of this attachment, they define an "easy direction" in the rarefied gas of space, like the grain in a piece of wood, a direction in which ions and electrons, as well as electric currents (and certain radio-type waves), can easily move; in contrast, motion from one line to another is more difficult.

A map of the magnetic field lines of the magnetosphere, like the one displayed above (from a mathematical model of the field), tells at a glance how different regions are linked and many other important properties.

Electromagnetic Waves    Faraday not only viewed the space around a magnet as filled with field lines, but also developed an intuitive (and perhaps mystical) notion that such space was itself modified, even if it was a complete vacuum. His younger contemporary, the great Scottish physicist James Clerk Maxwell, placed this notion on a firm mathematical footing, including in it electrical forces as well as magnetic ones. Such a modified space is now known as an electromagnetic field.     Today electromagnetic fields (and other types of field as well) are a cornerstone of physics. Their basic equations, derived by Maxwell, suggested that they could undergo wave motion, spreading with the speed of light, and Maxwell correctly guessed that this actually was light and that light was in fact an electromagnetic wave.

Heinrich Hertz in Germany, soon afterwards, produced such waves by electrical means, in the first laboratory demonstration of radio waves. Nowadays a wide variety of such waves is known, from radio (very long waves, relatively low frequency) to microwaves, infra-red, visible light, ultra-violet, x-rays and gamma rays (very short waves, extremely high frequency).

    Radio waves produced in our magnetosphere are often modified by their environment and tell us about the particles trapped there. Other such waves have been detected from the magnetospheres of distant planets, the Sun and the distant universe. X-rays, too, are observed to come from such sources and are the signatures of high-energy electrons there.

        Author and Curator:   Dr. David P. Stern     Co-author: Dr. Mauricio Peredo

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Magnetism and magnetic fields An phenomenon apparently unrelated to electricity is magnetism. We are familiar with magnetism through the interaction of compasses with the earth's magnetic field, or through fridge magnets or magnets on children's toys. Magnetic forces are explained in terms very similar to those used for electric forces:

There are two types of magnetic poles, conventionally called North and South

Like poles repel, and opposite poles attract However, magnetism differs from electricity in one important aspect:

Unlike electric charges, magnetic poles always occur in North-South pairs; there are no magnetic monopoles.

Later on we will see at the atomic level why this is so. As in the case of electric charges, it is convenient to introduce the concept of a magnetic field in describing the action of magnetic forces. Magnetic field lines for a bar magnet are pictured below.

  Figure 9.5: Magnetic field lines of a bar magnet

One can interpret these lines as indicating the direction that a compass needle will point if placed at that position. The strength of magnetic fields is measured in units of Teslas (T). One tesla is actually a relatively strong field - the earth's magnetic field is of the order of 0.0001 T.

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Magnetism from electricity

A connection between electricity and magnetism was discovered (accidentally) by Orsted over 100 years ago, who noticed that a compass needle is deflected when brought into the vicinity of a current carrying wire. Thus, currents induce in their vicinity magnetic fields. An electromagnet is simply a coil of wires which, when a current is passed through, generate a magnetic field, as below.

Figure 9.10: Electromagnet

Another example of this effect at work is in an atom, such as pictured in Fig. 9.1 - since an electron is a charge which moves about the nucleus, in effect it forms a current loop, and hence a magnetic field may be associated with an individual atom. It is this basic property which is believed to be the origin of the magnetic properties of various types of materials found in nature, as we shall now discuss.

Speaker Another device which uses the magnetic forces existing on current carrying wires is the speaker. A speaker is a device which takes an electrical signal (which was at one time a sound wave), and converts it back into a sound wave. A basic speaker is pictured below.

Figure 9.9: Basic speaker / microphone

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In the speaker, electrical signals in the form of an AC current are sent through a loop which is immersed in a magnetic field. This loop thus experiences a force, which is is transferred to the attached speaker membrane. Because the current is alternating, the speaker membrane is alternatively pushed to the left and then to the right in the figure. These vibrations cause air molecules to start to vibrate, which causes a sound wave to be generated, which our ears interpret as sound. By modulating the strength and frequency of the current, it is possible to change the amplitude and frequency of oscillation of the speaker membrane. This results in a corresponding change in the volume, and pitch of the resulting sound.

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Voltage of an Electric EEL The Physics Factbook™

Edited by Glenn Elert -- Written by his studentsAn educational, Fair Use website

Bibliographic EntryResult

(w/surrounding text)Standardized

Result

Kent, George C. Comparative Anatomy of the Vertebrates. USA: Mosby Year Book, 1992.

"the potential produced by these organs in eels amounts to 600 volts"

600 V

"Electric Eel." Encyclopedia Britannica. Britannica. 1997: 426.

"the shock … can measure up to 650 volts" 650 V

Great Book of Animals. USA: Courage Books. 1997.

"and the other of a high voltage, 100 V in specimens of about four inches (10 cm) and

500 V in those over 3 feet (1 m)"100–500 V

Whitfield, Phillip. "Electric Eel." MacMillan Illustrated Animal Encyclopedia. New York: MacMillan, 1984: 512.

"which produces a charge … which may amount to 500 V"

500 V

The electric eel (Electrophorus electricus), which is found in South American tropical regions, has the ability to produce powerful electric charges. The low intensity charges emitted by the eel range from 5 to 10 V. The higher intensity charges vary by the size of the eel. Smaller eels (about 10 cm in length) can produce charges of up to 100 V. Larger eels (over 1 m in length) can produce charges of 450 to 650 volts of electricity. The discharging system of the electric cells was first explained by a Martins-Ferreira, Altamirano and Keynes in 1953.

The electric organs of the eel are located in its tail, which is roughly 4/5 of the animal's body. The electric organs are made up of a large number of electric disks (as many as 200,000 in one tail) piled in vertical or horizontal rows. The nerve endings located at the end of the electroplax discharge the electricity.

The electric organs are used many different ways by the electric eel. The low intensity impulses are used by the eel for sensory perception. This helps it navigate in its habitat (muddy streams) where vision is blocked. The low intensity impulses are also used for communication. The high intensity charges are used for stunning or killing smaller fish. The charge is also used for the eel to defend itself.

The electric eel is one of the few animals on the planet that can make, store, and discharge electricity. The actual amount it discharges is debatable. However, 500 V is the most accepted value to express the electric current produced by an electric eel.

Barry Lajnwand – 1999

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Bibliographic EntryResult

(w/surrounding text)Standardized

Result

The New Book of Popular Science 4th ed. China: Grolier, 1978.

"Gymnotid eels of the genus Electrophorous can produce charges of over 500 volts"

500 V

"Electric Eel." World Book Encyclopedia. Chicago: World Book, 1997.

"Each electroplaque gives off a small charge of electricity …. The charges [sic] of all these

electroplaques combine to produce 350–650 V."350–650 V

Argo, Joseph. Electric   Eel . MAD Scientist Network. Washington University Medical School. 28 August 1997.

"They generally release a charge [sic] of about 25-75 volts but can get as powerful as 500 volts (some have been reported to be up to 800 volts, but this is

an unconfirmed report)"

25–75 V(typical)

500 V(maximum)

800 V(unconfirmed)

Prappas, Jim. Electric   Eel . Pittsburgh Zoo.

"Feeding: Eat other fish, killing them with electric shock (up to 600 Volts)."

600 V

The electric eel (Electrophorous electricus) is not considered a true eel. Although it looks like other eels, it is quite different. The electric eel has different habits, and is commonly known for its ability to generate an electric current. It is a spineless, toothless fish that grows up to three feet long and is found in the Amazon and other South American rivers.

The characteristics of the electric eel which makes it unique, is the electric voltage that it produces. The body of the electric eel is mostly made up of an organ that produces electricity. Like a battery the electric eel has two opposite poles (the head and the tail), and when they discharge, the voltage flows from either the head or the tail.

The organ in the electric eel that enables it to produce electricity is made up of 5,000 to 6,000 electroplaques (set up much like the cells in a dry battery). Each electroplaque produces only a small voltage, but when all the electroplaque are all arranged in series (as they are in the body of the electric eel) you get a large jolt. It can produce voltages of up to 500 to 650 volts. This is five times the voltage that comes out a wall socket, and is strong enough to injure or even kill a human.

The question that remains to be answered is, why does the electric eel have this strange ability? The answer is quite simple, the electric eel uses it ability to produce electricity to hunt for food. The charge from the eel kills its prey allowing the electric eel to swallow it. They need to do this because they have no teeth, and can only feed on prey that is not moving. Although the electric eel can produce large voltages it is the current that kills and not the voltage.

Dafe Okodiko – 1999

Electric eels are not eels. They are fish of the family Gymnotidae. They can produce electric currents. These serpentine fish can produce paralyzing discharges with their

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powerful electric organs. The powerful electric organs lie on either side of the vertebral column. These electric organs have around 5,000 to 6,000 electroplates which are arranged like cells in a battery. The organ emits 2 kinds of discharges, a high voltage one and a weaker one. The high voltage discharge can go up to around one ampere at 500 volts. It is usually for stunning prey. The weaker discharge is used for direction and as an indicator for locating objects. Electric eels have been known to knock down a horse crossing a stream from 20 feet away not to mention also killing humans. They are also known to still emit discharge eight to nine hours after their death. The shock from an electric eel affects the body by altering physiological functions such as involuntary muscle actions and respiration. Symptoms of being shocked by an electric eel can be respiratory paralysis and cardiac failure. These symptoms may result in death.

Sunny Feng -- 2000

Related pages in The Physics Factbook:

Electric Current from an Electric Eel

External links to this page:

Guardian Unlimited, Simon Jeffery, 8 April 2002

o Guardian | Eels

o Eels | News | guardian.co.uk

Hobbsblog II: adventures in Duluth , Nathan Hobbs

(The electric eel can generate up to a 500 volt charge….ouch!)

NAME: LEVEL: DATE:

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CHECK LIST FOR ELECTRICITY & MAGNETISM PACKET

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1) The student completed all vocabulary associated with this learning guide to 100% accuracy.

25

2) The student completed all written work associated with this learning guide to 100% accuracy.

25

3) The student completed post-test to 80% accuracy. 204) The student recorded all project results to 90% accuracy. 205) The student is able to explain the parts and operation of a basic transformer.

25

6) The student completed project # 1. 257) The student completed project # 2. 258) The student completed project # 3. 259) The student completed project # 4. 2510) The student completed project # 5. 2511) The student completed the written assessment to 80% accuracy. 20

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MAGNETISM PACKET ASSESSMENT(Post Test)

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PointsAvailable

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Correct/Out of 260 Grade Percentage Check One Percentage Task Grade

Below Basic 0%-69% 0-6 Basic 70%-85% 7 Competent 86%-92% 8-9 Advanced 93%-100% 10

CC.1.3.11-12.I Determine or clarify the meaning of unknown and multiple-meaning words and phrases based on grade level reading and content, choosing flexibly from a range of strategies and tools.CC.1.4.11-12.A Write informative/ explanatory texts to examine and convey complex ideas, concepts, and information clearly and accurately.

True/FalseIndicate whether the sentence or statement is true or false.

____ 1. The earth is a really big natural magnet.

____ 2. Magnetic lines of force flow from one pole of a magnet to the other pole.

Multiple ChoiceIdentify the letter of the choice that best completes the statement or answers the question.

____ 3. Lodestone is a name for a naturally occurring magnetic material that is also calleda. leadb. magnetismc. copperd. magnetite

____ 4. Leading stone is another name for natural magnets which are also calleda. lodestoneb. magnetitec. both a and b

____ 5. The geographic north pole of the earth is magnetically a _____ pole.a. northb. south

____ 6. A(n) _____ magnet is a magnet that retains its magnetism without any applied power.a. electrob. permanentc. temporaryd. domain

____ 7. Permanent magnets retain their magnetisma. only if external power is appliedb. without any external power

____ 8. The three substances that form natural magnets area. iron, boron, and cobaltb. copper, iron, and cobaltc. copper, nickel, and borond. iron, nickel, and cobalt

____ 9. Magnetism can be explained in terms of _____ spin patterns.a. electronb. neutronc. protond. quark

______10. The regions formed in the molecular structure of magnetic metals by unpaired electrons is sometimes called magnetic

a. areasb. spins

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c. domainsd. atoms

____ 11. Electrons in orbit around the nucleus of an atom have magnetic fields. Most of the electrons in most materials pair up in such a way that their magnetic fields _____ leaving the materials nonmagnetic.a. addb. cancel

____ 12. Magnetic lines of force are calleda. fluxb. spinc. reluctanced. bands

____ 13. A basic law of magnetism states that like poles _____ and opposite poles _____.a. attract, repelb. repel, attract

____ 14. A magnet that produces a magnetic field as the result of current flow in a conductor is called a(n) _____ magnet.a. electrob. permanentc. temporaryd. domain

____ 15. The strength of an electromagnet is primarily proportional to itsa. lengthb. ampere-turnsc. diameterd. core resistance

____ 16. The measure of a material’s willingness to be magnetized is calleda. permeabilityb. reluctancec. saturationd. residual magnetism

____ 17. The measure of a material’s resistance to being magnetized is calleda. permeabilityb. reluctancec. saturationd. residual magnetism

____ 18. When a magnetic materials molecules are all lined up, and increases in current flow no longer cause increases in magnetic field strength, the material has reacheda. permeabilityb. reluctancec. saturationd. residual magnetism

____ 19. The amount of magnetism left in a material after the magnetizing current has been removed is a. permeabilityb. reluctancec. saturation

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d. residual magnetism____ 20. The strength of a magnetic field is an indication of how many flux lines per square inch there are.

This is calleda. residual magnetismb. reluctancec. permeabilityd. flux density

____ 21. In the English system, the total force producing a magnetic field is thea. magnetomotive forceb. reluctancec. permeabilityd. flux density

____ 22. To locate the north pole of an electromagnet, use the _____ hand rule.a. leftb. right

____ 23. If an object is placed in the field of an AC electromagnet and slowly moved away, the object will bea. demagnetizedb. magnetized

CompletionComplete each sentence or statement.

24. Like magnetic poles _______________.

25. Opposite magnetic poles _______________.

Residential & Industrial ElectricityK-W-L WORKSHEET

48

NAME: LEVEL: DATE:

ARTICLE TITLE:

TIME START: TIME FINISH:

K What do I already KNOW about this topic?

W What do I WANT to know about this topic?

L What did I LEARN after reading ABOUT this topic?

I checked the following before reading: Headlines and Subheadings Italic, Bold, and Underlined words Pictures, Tables, and Graphs Questions or other key information

I made predictions AFTER previewing the article.

Comments:

Instructor Signature:

NAME: DATE:

49

MAGNETISM PACKET ASSESSMENT(Pre Test)

CC.1.3.11-12.I Determine or clarify the meaning of unknown and multiple-meaning words and phrases based on grade level reading and content, choosing flexibly from a range of strategies and tools.CC.1.4.11-12.A Write informative/ explanatory texts to examine and convey complex ideas, concepts, and information clearly and accurately.

True/FalseIndicate whether the sentence or statement is true or false.

____ 1. The earth is a really big natural magnet.

____ 2. Magnetic lines of force flow from one pole of a magnet to the other pole.

Multiple ChoiceIdentify the letter of the choice that best completes the statement or answers the question.

____ 3. Lodestone is a name for a naturally occurring magnetic material that is also calleda. leadb. magnetismc. copperd. magnetite

____ 4. Leading stone is another name for natural magnets which are also calleda. lodestoneb. magnetitec. both a and b

____ 5. The geographic north pole of the earth is magnetically a _____ pole.a. northb. south

____ 6. A(n) _____ magnet is a magnet that retains its magnetism without any applied power.a. electrob. permanentc. temporaryd. domain

____ 7. Permanent magnets retain their magnetisma. only if external power is appliedb. without any external power

____ 8. The three substances that form natural magnets area. iron, boron, and cobaltb. copper, iron, and cobaltc. copper, nickel, and borond. iron, nickel, and cobalt

____ 9. Magnetism can be explained in terms of _____ spin patterns.a. electronb. neutronc. protond. quark

______10. The regions formed in the molecular structure of magnetic metals by unpaired electrons is sometimes called magnetic

50

a. areasb. spinsc. domainsd. atoms

____ 11. Electrons in orbit around the nucleus of an atom have magnetic fields. Most of the electrons in most materials pair up in such a way that their magnetic fields _____ leaving the materials nonmagnetic.a. addb. cancel

____ 12. Magnetic lines of force are calleda. fluxb. spinc. reluctanced. bands

____ 13. A basic law of magnetism states that like poles _____ and opposite poles _____.a. attract, repelb. repel, attract

____ 14. A magnet that produces a magnetic field as the result of current flow in a conductor is called a(n) _____ magnet.a. electrob. permanentc. temporaryd. domain

____ 15. The strength of an electromagnet is primarily proportional to itsa. lengthb. ampere-turnsc. diameterd. core resistance

____ 16. The measure of a material’s willingness to be magnetized is calleda. permeabilityb. reluctancec. saturationd. residual magnetism

____ 17. The measure of a material’s resistance to being magnetized is calleda. permeabilityb. reluctancec. saturationd. residual magnetism

____ 18. When a magnetic materials molecules are all lined up, and increases in current flow no longer cause increases in magnetic field strength, the material has reacheda. permeabilityb. reluctancec. saturationd. residual magnetism

____ 19. The amount of magnetism left in a material after the magnetizing current has been removed is a. permeability

51

b. reluctancec. saturationd. residual magnetism

____ 20. The strength of a magnetic field is an indication of how many flux lines per square inch there are. This is calleda. residual magnetismb. reluctancec. permeabilityd. flux density

____ 21. In the English system, the total force producing a magnetic field is thea. magnetomotive forceb. reluctancec. permeabilityd. flux density

____ 22. To locate the north pole of an electromagnet, use the _____ hand rule.a. leftb. right

____ 23. If an object is placed in the field of an AC electromagnet and slowly moved away, the object will bea. demagnetizedb. magnetized

CompletionComplete each sentence or statement.

24. Like magnetic poles _______________.

25. Opposite magnetic poles _______________.

52