Elizabeth R. C. Cregan

TCM 10575

Physical Science

Science ReadeRS

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Elizabeth R. C. Cregan, MDE

Teacher Created Materials Publishing 5301 Oceanus Drive

Huntington Beach, CA 92649-1030 http://www.tcmpub.com

ISBN 978-0-7439-0575-6 © 2007 Teacher Created Materials Publishing

The Electromagnetic Force .............................................. 4

Atoms at Work ................................................................ 6

Electricity ........................................................................ 8

Magnetism ..................................................................... 10

Invisible Lines of Force .................................................. 14

Generators Get Electricity Flowing ............................... 16

Amps, Volts, and Watts .................................................. 18

AC and DC Currents ..................................................... 20

Powering Communications ............................................ 22

Into the Future .............................................................. 26

Appendices .................................................................... 28

Lab: Create an Electromagnet .......................... 28

Glossary ........................................................... 30

Index ................................................................ 31

Sally Ride Science ............................................. 32

Image Credits ................................................... 32

Table of Contents

Editorial Director Dona Herweck Rice

Associate Editor Joshua BishopRoby

Editor-in-Chief Sharon Coan, M.S.Ed.

Creative Director Lee Aucoin

Illustration Manager Timothy J. Bradley

Publisher Rachelle Cracchiolo, M.S.Ed.

Publishing Credits

Science Contributor Sally Ride Science

Science Consultants Michael E. Kopecky, Science Department Chair, Chino Hills High School Jane Weir, MPhys

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Physical Science Readers:Investigating Electromagnetism

You may not know it, but you use electromagnets (uh-lek-troh-MAG-nuhts) many times every day. They are everywhere. They produce electricity (uh-lek-TRIS-i-tee) for homes. Magnetism is used to store data in computers. Electromagnets bring pictures to television screens. Nearly everything we do is affected by electromagnets. Without them, the world would be very different.

Electromagnetism is a powerful force. It is the combined power of electricity and magnetism.

People have always been curious about electricity and magnetism. The ancient Chinese and Greeks observed magnetism in a mineral called lodestone. Lodestone attracts tiny bits of iron.

In 1752, Benjamin Franklin wrote a paper on what might happen in an experiment in which one flew a kite in a storm. There’s no proof that he actually did it. Others did, and they electrocuted themselves more often than not!

Benjamin Franklin and what he might have looked like while experimenting with electricity in a storm

Present-Day Magnesia

A piece of magnetite, also known as

lodestone.

Where Magnets Got Their NameLodestone was very common in Magnesia (mag-NEE-zhuh) . Magnets were named after this area of Greece.

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The Electromagnetic Force

So, how does electromagnetism work? The story begins with nature’s building block. It is the atom.

Everything in nature is made up of matter. Matter is made up of tiny particles called atoms.

At the center of the atom is a nucleus (NOO-klee-uhs). Inside the nucleus are tiny particles (PAR-tuh-kuhls) called protons and neutrons. Protons have positive electric charges. Neutrons have no charge.

Circling around the nucleus are clouds of really small particles called electrons. Electrons carry a negative charge.

Each atom has the same number of electrons and protons. It is the attraction of these opposite charges to each other that holds the atom together.

In some atoms, the electrons can break free of the atom and join another atom. As these electrons jump from atom to atom, an electrical charge is created. Electricity is the energy created

by the movement of electrons.

Electromagnetic Field of an Atom Each electron in an atom spins around the nucleus.

This creates a weak electromagnetic field. A field is a region where a force acts.

electrons

proton

neutron

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Atoms at Work

As the electrons move through a conductor, such as your electrical wire, the electrical charge creates a current of electricity to provide power.

Let’s take a closer look at electricity. There are two types of electricity. They are static and current.

Shuffle your feet across a carpet. Then touch your friend’s hand. You may both feel a small shock. This shock is really a tiny jolt of static electricity.

Until electricity is able to move, it is at rest. That is called static. When you shuffle your feet on a carpet, you transfer electrons from one surface to the other. This makes one surface positively charged and the other negatively charged. This difference in charges is called a “potential difference.” When you touch your friend’s hand, the jolt you feel is the electrons moving from one hand to the other. This evens out the potential difference and makes both surfaces neutral again.

An electrical current is the flow of electrons from one place to another. For a current to flow, there must be an electrical circuit (SIR-kit). This is a closed loop of conducting material that the electricity can flow along.

Did You Know?In the 19th century, sweethearts enjoyed sharing “electric kisses.” They would shuffle their feet across a rug and then kiss. The kiss would include a small jolt of static electricity.

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Electricity

Now, let’s take a closer look at magnetism. Magnetism creates an invisible force that only affects certain things. Iron is one of these things. Magnetic forces can move a piece of iron without anything touching the metal.

Magnetism can only reach so far, though. The reach of a magnet is called its magnetic field. Magnetic forces can be felt within the field but not outside it. A magnetic field is made of invisible lines of force. The lines go from one end of the magnet to the other end. The ends are called the north and south poles.

If you place the north pole of one magnet next to the south pole of another magnet, something interesting happens. The invisible magnetic fields pull on each other. The magnets attract. This means they move to stick together.

If you place the north pole of one magnet next to the north pole of another magnet, they repel. This means they move apart. The magnetic fields push on each other.

10 11

Magnetism

Did You Know?When the ancient Chinese tied a string around a piece of lodestone and hung it in the air, the stone pointed north. The lodestone acted as a compass. Chinese military leaders were probably the first to use compasses.

Take a Closer LookA magnet’s north and south poles are attracted to the north and south poles of the earth. This is how a compass works. Earth’s magnetic field makes the earth act as if it has a giant bar magnet running through its center. Earth’s north pole actually behaves like a magnet’s south pole. In other words, a bar magnet’s north pole is attracted to it.

Big Ideas About Magnets• The field lines of a magnet go

from north to south.

• Magnetic force is strongest at a magnet’s ends.

• Magnetic force is stronger the closer you are to a magnet.

• If you cut a magnet in half, each piece will become a magnet with north and south poles.

You can see the magnetic fields of these two magnets in the iron filings around them. The iron filings line up along the lines of force.

The first known magnets were natural ones, like lodestone. Scientists began to wonder if they could make artificial (ar-tuh-FISH-uhl) magnets, too. Artificial means something that is man-made.

In 1820, one scientist found a way. At a party, Hans Oersted placed a compass near an electrical current. He noticed that the needle on the compass moved. The electrical current had made a magnetic field. Oersted investigated further. He found that electrical currents have magnetic fields that go around the wire.

This showed that there is a close relationship between electricity and magnetism. And that led to the discovery of the electromagnet. An electromagnet is a device that is found in everything from telephones to the motors in washing machines.

A simple electromagnet is a coil of wire attached to the negative and positive ends of a battery. Electrons flow from the negative end of the battery through the wire. They arrive at the positive end of the battery. This flow of electricity creates a small magnetic field around the wire.

An electromagnet can be made stronger by using more turns or wires in the coil or more current in the circuit. A piece of soft iron like a nail put through the coil makes the electromagnet stronger still.

Electromagnets Move MotorsAt the heart of every electric

motor is an electromagnet. When you put magnets next to each other, magnetic forces act between them to repel or attract each other. Electric motors use this to create motion that spins or rotates. This rotating motion is used to power everything from electric fans to cars.

Electromagnets can be created in many different ways. Notice that each of these contains a coil of wire attached to the negative and

positive ends of a battery.

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In the 1830s, Michael Faraday (FAR-uh-day) wondered how electricity and magnetism were related. Faraday was a scientist in England. He liked to experiment with different scientific ideas.

Faraday’s work proved that electricity and magnetism were different ways to observe a “single unified force.” He called this force electromagnetism.

Faraday’s ideas likely led others to see electricity as useful in their inventions. His ideas were critical to the invention of the dynamo. That was the first electrical generator (JEN-uh-ray-ter). It could provide enough power to make machines work.

Michael Faraday

Lighting the Bike PathThe idea behind Faraday’s dynamo is a common way to make electricity for use in bike lights. Energy produced by pedaling the bike is changed into electric current. That keeps the lamp lit.

The dynamo was invented in 1832.

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Invisible Lines of Force

What exactly is a generator, and how does it work? An electrical generator converts energy from other sources into electrical energy. This energy is what makes a light or a television work when switched on. When this energy is made, electricity and magnetism are at work. To better understand how these forces work, let’s take a look at how an electrical current and electromagnetism are made.

First, electricity needs a conductor to move it from one point to another. Materials that are good conductors have electrons that move easily. Copper wire is a good conductor. Aluminum, gold, and silver are other metals that are sometimes used as conductors.

Electricity also needs something to get it moving through the conductor. Generators are often used to do this.

We know that an electrical current moving through a wire creates a magnetic field. Generators work in the opposite way. Generators use magnets to push the electricity along a wire. This creates a steady flow of electricity.

Imagine a pipe. This represents the wire. It is filled with ping-pong balls. What would happen if you pushed one more ball into the end? All the balls would move along the pipe and bump the last one out. This is like electrons moving along the wire and into an electrical appliance.

Generators like these create electricity.

This is an X-ray of a hand-crank flashlight. It is started by pressing the handle. The handle is connected to a generator that creates electricity for the light bulb.

generator

Electrons travel along the red wire to the bulb.

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Generators Get Electricity Flowing

As a generator’s magnet pushes the electricity along the wire, two things happen. The magnet pushes a specific number of electrons along the wire. This electrical current is measured in amperes (AM-peers), or amps. The magnet is also putting pressure on the electrons. This pressure is measured in volts.

Think about how these ideas might be related to your home or school building. Power outlets deliver volts to an electrical device. The flow from the outlet to the device is then measured in amps.

Amps and volts are put together to determine how much power is being used. This is measured in watts. Watts are found by multiplying the amps and volts together. That tells you how many electrons are moving and how much force is behind all those electrons.

Battery PowerThe batteries you use to run

your radio or CD player are actually chemical batteries. Metals and acids inside the batteries react to free electrons near the negative end of the battery. That is the end with the small dent. When you place the batteries inside your CD player, the electrons travel from the negative end of the battery through the CD player, and back to the positive end. That is the end with the tiny post. The CD player uses this flow of electricity to play your favorite tunes.

This is an X-ray of the inside of a CD player. The yellow circle shows the location of the laser that reads the CD. The solid red lines and arrows show the direction of electrical power moving from the batteries to the circuit board and back.

Did You Know?The volt is named after Alessandro Volta. Volta invented the first electric battery in 1799. The watt is named after James Watt who invented the steam engine.

Battery Power!Annie Easley is a modern scientist working with batteries. But these are not just any batteries. She develops computer codes for NASA to help find the best and longest-lasting batteries for electric utility vehicles.

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Amps, Volts, and Watts

After Thomas Edison invented the light bulb in 1879, he worked to bring

electricity into people’s homes. He also made a promise. He wanted to light up the city of New York. There was a problem, though. The electricity for homes was direct current, or DC. This is a current pushed through a circuit and flowing continuously in the same direction.

Low-voltage DC currents cannot travel long distances because

there are such high losses in the cables that carry them. That means

DC is not good for powering our homes.

Nikola Tesla, who worked for Thomas Edison, had an idea. He wanted to use another

kind of electric current. Alternating current, or AC, can change direction many times in one second. This makes it easy for electricity to travel over long distances.

The two men didn’t agree. In the end, Tesla’s ideas worked best. Today, the electricity that comes from a power plant and is used in our homes is AC.

+–

Battery(source) Light

(load)

Wires

Circuits: The Electric HighwayCircuits are the paths that an electric current follows as it moves through a conductor such as a copper wire. All circuits have a source, a load, and two wires to lead to and from the source. Circuits must be unbroken. If there is a break in the conductor, then the electricity can’t get through and the circuit won’t work.

Changing PowerDifferent countries use different AC power. For example, in the United States, an AC changes 60 times in one second. In Europe, it changes 50 times in one second. This is why some electrical devices don’t work in power outlets in other countries without an adaptor like the one shown below.

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AC and DC Currents

TransformersAC electricity can travel long distances because of transformers. They are devices that transmit the voltage. Transformers don’t work with DC.

Nikola Tesla

This is a drawing of a simple circuit. Some complete circuits are so small that they can fit on the edge of

a penny!

Inventions that used electricity improved the ways we communicate with each other.

The invention of the telegraph was the first time electricity was put to a practical use. In 1844, Samuel Morse created the first telegraph line. This line connected Washington, D.C., to Baltimore, Maryland. His telegraph was a very simple device. It used a battery, a switch, and a small electromagnet to send small bursts of electricity through a wire. He invented Morse code to communicate through the telegraph wires.

People enjoyed the ability to communicate by telegraph. But what they really wanted was to hear the voices of loved ones who lived far away. In 1875, the people got their wish. Alexander Graham Bell invented the telephone. Now the world had a way to communicate over long distances.

Take a Closer LookMorse code is a special language of dots (short electric signals) and dashes (longer electric signals). It was designed just for the telegraph. Different combinations of dots and dashes represented letters of the alphabet.

Railroad CommunicationsTo run safely, the railroads needed a way to communicate. Mattie “Ma” Kiley was one of the first female telegraphers to work for the railroads. Dispatchers used the telegraph to share information. Kiley worked in railroad telegraphy until she retired in 1942.

Early telegraph

Mattie “Ma” Kiley

MorseCode

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Powering Communications

Electromagnetism is the force behind any electronic gadget, including many communication tools. The personal computer and cell phone are two examples. These machines keep getting smaller. The tiny devices that power these gadgets are called transistors (tran-ZIS-ters) and microchips.

Transistors use electricity to turn electricity on and off. It’s a very clever switch. Scientists soon learned how to make transistors smaller and even more powerful.

Scientists also learned how to put entire electrical circuits on small pieces of silicon known as microchips. This made it possible to build small, powerful devices such as laptop computers and cell phones. It is now possible to place millions of tiny transistors and circuits onto one chip.

Scientists continue to learn more about how to use electricity and electromagnetic waves in newer and more powerful tools.

Solar EnergyWould you like to carry around

electricity wherever you go—without lugging batteries? A solar panel might do the trick. Using the power of the sun is one of the best ways to make electricity. Solar panels are made of a thin layer of a semiconductor, like silicon, and thin strips of metal. As sunlight hits the panel, the silicon absorbs it. Electrons are knocked loose and flow freely. The metal strips use the electricity to do work such as powering your radio.

Disposable PhonesIn 1999, Randice-Lisa Altschul made the first disposable cell phone. She thought of the idea after being frustrated with a bad connection. Altschul imagined throwing her phone out the window. Then the idea came to her!

Transistors and microchips continue to grow smaller. These transistors are enlarged so that you can see the detail from the microchip being held.

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So what does the future hold for us? Laser light is one example. It is a new form of energy that relies on electromagnetic force. Scientists discovered a way to use the energy created by atoms and their electrons. A laser beam is created when light energy is captured and concentrated.

Lasers are used in many different ways. Doctors use lasers to operate on patients. The grocery clerk uses lasers to scan your cereal and milk at the checkout counter. You even use lasers when you listen to a CD player—a tiny laser plays the music stored on the compact disc.

Electromagnetism has changed our world. It has changed how we live every day. From Franklin’s kite to laser beams, we have learned a great deal about using electricity and magnetism to power our world. Consider the possibilities for the future. There’s no telling what scientists will think of in the years to come.

MRIDoctors often use Magnetic

Resonance Imaging (MRI) to find out if something is wrong inside a patient. They don’t have to cut open the patient to look. They can see inside the body with MRI. It works through the use of a powerful magnet. The magnet affects the hydrogen atoms in the body. They behave in a way that lets images inside the body be seen with radio frequency pulses. It’s complicated, but it works!

The magnet used in an MRI scanner is so powerful that metal objects can’t be taken in the same room with it. Normally harmless things such as paper clips and pens can become dangerous. They would be pulled by the powerful magnetic strength and fly directly at the patient in the center of the MRI machine. That is where the magnet has its greatest power. Even something as big and heavy as a metal pipe would be pulled from someone’s grasp if the person were near the MRI machine!

This is an electron micrograph of human nerve cells growing on the surface of a circuit.

Such circuits are too small for you to see. They combine organic (living) and

inorganic components.

Take a LookPeople who couldn’t “take a look” have a chance to do so now. It’s all because of Patricia Bath. She developed the laserphacoprobe. It uses a laser beam to break up cataracts. Cataracts are a disease of the eye that causes blurry vision.

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Into the Future

Let’s Experiment

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Electrical currents produce magnetic fields around them. When you make a coil out of conducting wire, you can strengthen the magnetic field. This device is called an electromagnet. The more coils of wire, the stronger the magnetic field. You can add a piece of metal, too. This makes the electromagnet even stronger.

Try this.

Materials• a 2-inch iron nail

• heavy, insulated wire

• two D-cell batteries

• 10 paper clips

• scraps of paper

• masking tape

Procedure1 Wrap 20 turns of wire around the nail.

2 Leave about 8 inches of wire hanging from each end of the coil around the nail.

3 Peel back 3 inches of the insulating material from each end of the wire.

4 Tape the positive end of one D-cell battery to the negative end of the second battery.

5 Tape one end of the wire to the positive end of the batteries and one end to the negative end of the batteries.

6 Make a pile of paper clips and a pile of paper scraps.

7 Run the nail with the coiled wire over the paper clips and the scraps of paper. Observe what happens.

8 Try steps 1 through 7 again, but this time coil the wire tighter in step 2. Create an electromagnet with 50 turns around the nail.

9 Make another pile of paper clips.

10 Run the nail with the coiled wire over the paper clips. Observe what happens.

11 Record your results.

ExtensionWhat makes a better electromagnet:

more electricity or more coils around the nail? Create an experiment to find out.

Try using materials other than the nail. Try a pencil. Try a pen. Try a crayon. Do they work? How well? Why do you think this is so?

Lab: Create an Electromagnet1

7

8

alternating current (AC)�—an electrical current in which the electrons move one way, then the other

ampere (amp)�—unit of measure for a current

atom—the smallest particle of an element

battery—a device that produces electricity to provide power for radios, cars, toys, etc.

circuit—the path that an electric current follows as it moves through a conductor

compass—a device used to determine direction (north, south, east or west)

conductor—a type of material that allows electricity to flow through it

direct current (DC)�—an electrical current in which the electrons move in one direction

electrical current (current)�—the flow of electrons from one place to another

electricity—a form of energy possessed by electrons and protons as a result of their electric charge (positive and negative)

electromagnetism–magnetism produced by an electric current

electromagnet—magnet made using coiled, current-carrying wires

electron—negatively charged particle inside an atom

field—region where a force acts

generator—a machine that changes mechanical energy into electrical energy

laser—a device that creates a very narrow beam of light by amplifying focused, coherent light

lodestone—a type of mineral with natural magnetic properties

magnetic field—region in which a magnetic force acts

magnetism—the property of magnets that allow them to attract iron

magnet—object that is able to attract iron and steel objects and also to push them away

microchip—very small electronic part that contains extremely small electronic circuits and devices

neutron—particle found in the nucleus of an atom with a neutral electrical charge

nucleus—the dense center of an atom made up of protons and neutrons

proton—particle found in the nucleus of an atom with a positive electrical charge

static electricity—an electrical charge that collects on the surface of objects made from rubbing together certain types of material

telegraph—an electrical device used to send messages over a wire

transformer—device used to step voltage up and down so that AC electricity can be transmitted over distances

transistor—small electrical device containing semiconductors, used in televisions, radios, etc., to control or increase an electric current

volt—unit of measure for the force of an electrical current

watt—unit of measure of electric power

alternating current (AC), 20–21

ampere (amp), 18

atom, 6–7

Altschul, Randice-Lisa, 25

battery, 12–13, 18–19, 21–22, 25, 28–29

Bath, Patricia, 26

Bell, Alexander Graham, 22

circuit, 9, 12, 19–21, 26

compass, 10–12

conductor, 6, 16, 21

current, see electrical current

direct current (DC), 20–21

Edison, Thomas, 20

electrical current, 9, 12, 16–18, 20–21, 28–29

electricity, 4–9, 12–26, 28–29

electromagnet, 4–5, 12–13, 22, 28–29

electron, 6–9, 16–19, 25–26

Faraday, Michael, 14–15

field, 7, 10–12

Franklin, Benjamin, 5, 26

generator, 14–18

Kiley, Mattie “Ma,” 23

laser, 19, 26

lodestone, 5, 10, 12

magnetic field, 7, 10–12, 17, 28–29

magnetism, 4–7, 10–14, 16, 26

magnet, 5, 10–13, 17–18, 27

matter, 6

microchip, 24

Morse, Samuel, 22

Morse code, 22–23

MRI, 27

neutron, 6–7

nucleus, 6–7

proton, 6–7

solar energy, 25

static electricity, 8–9

telegraph, 22–23

Tesla, Nikola, 20

transformer, 21

transistors, 24

volt, 18–19

Volta, Alessandro, 19

watt, 18–19

Watt, James, 19

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Glossary Index

32

Sally Ride Science

Image CreditsCover: p.3 Michael Chamberlin/Shutterstock; p.4 (top) Photos.com; p.4 (bottom) The Granger Collection, New York; p.5 (left) Tim Bradley; p.5 (right) Tim Bradley; p.5 (bottom) Alexander Maksimov/Shutterstock; p.6 (top) Tim Bradley; p.6 (bottom) Tim Bradley; p.7 Tim Bradley; p.8 (top) Nir Levy/Shutterstock; p.8–9 Bobby Deal/RealDealPhoto/Shutterstock; p.9 The Granger Collection, New York; p.10 (top) Michal Strzelecki/Shutterstock; p.10 (bottom) Tim Bradley; p.10–11 Thomas Mounsey/Shutterstock; p.11 (top) Neo Edmund/Shutterstock; p12 James Steidl/Shutterstock; p.13 (back) Photos.com; p.13 (left) Courtesy of Kenyon College; p.13 (center) Courtesy of Kenyon College; p.13 (right) Courtesy of Kenyon College; p.14 (top) Dreamstime.com; p.14 (bottom) The Granger Collection, New York; p.14–15 Bettmann/Corbis; p.15 Meelis Endla/Shutterstock; p.16 (top) Albert Lozano/Shutterstock; p.16 (bottom) Anson Hung/Shutterstock; p.17 Edward Kinsman /Photo Researchers, Inc.; p.18 (top) Scott Rothstein/Shutterstock; p.18 (bottom) NASA; p. Gusto/Photo Researchers, Inc.; p.20 (top) Kevan O’Meara/Shutterstock; p.20 (bottom) Library of Congress; p.21 (top) Tim Bradley; p.21 (bottom) Kevan O’Meara/Shutterstock; p.21 (right) Bethan Collins/Shutterstock; p.22 (top) Scott Rothstein/Shutterstock; p.22 (bottom) Newton Page/Shutterstock; p.23 (bottom) Library of Congress; p.24 (top) Heintje Joseph T. Lee/Shutterstock; p.24 (left) Anyka/Shutterstock; p.24 (right) Heintje Joseph T. Lee/Shutterstock; p.25 Photos.com;; p.26 (top) Photos.com; p.26 (bottom) Synaptek / Photo Researchers, Inc.; p.27 Photos.com; p.28 Photos.com; p.29 Nicoll Rager Fuller; p.32 Getty Images

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