Electricity and Magnetism

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Written by David Dreier

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Electricity and Magnetism

A Science A–Z Physical Series

Word Count: 2,278

Written by David Dreier

www.sciencea-z.com

Key elements Used in this BooKthe Big idea: Since the late 1800s, electricity has brightened our homes and streets, powered our appliances, and enabled the development of computers, phones, and many other devices we rely on. Understanding what electricity is and how it becomes ready for our safe use helps us appreciate this energy source. Without magnets, we couldn’t generate electricity. Electricity and magnetism, and the relationship between the two, are fundamental to the workings of the modern world.Key words: alternating current, amperes, atoms, attract, charge, circuit, conductor, direct current, electric current, electricity, electromagnet, electromagnetism, electrons, generator, hydroelectric plant, insulator, ion, lines of force, magnetic field, magnetism, neutrons, north pole, nuclear power plant, nucleus, permanent magnet, power plant, protons, repel, resistance, shock, solar power plant, south pole, static electricity, temporary magnet, transformer, transmission lines, turbine, volts, watts

Key comprehension skills: Identify facts Other suitable comprehension skills: Compare and contrast; classify information; cause and effect; elements of a genre; interpret graphs, charts, and diagrams; using a glossary and boldfaced terms; using a table of contents and headings

Key reading strategy: Ask and answer questions Other suitable reading strategies: Connect to prior knowledge; summarize; visualize; retell

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illustration Credit: Pages 5–7,14: Learning A–Z

Electricity and Magnetism © Learning A–Z Written by David Dreier

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Electricity and Magnetism

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Introduction

Have you ever looked out a window at night and watched flashes of lightning split the night sky during a raging thunderstorm? You might be surprised to know that lightning is a natural form of electricity. In the last two hundred years, people have learned how to produce and harness electricity. Whenever you flip a switch to turn on a light, you are using electricity. Computers and televisions can’t work without electricity. Electricity has become such an important part of our everyday lives that it is difficult to imagine the world without it.

Magnetism is also a familiar part of our world. Perhaps you have played with magnets or use magnets on your refrigerator door. Did you know that magnetism is closely related to electricity? This book will teach you about electricity and magnetism, as well as how they are related.

Table of Contents

Introduction .............................................................. 4

What Is Electricity? .................................................. 5

The Two Kinds of Electricity .................................. 8Static Electricity ...................................................... 8 Electric Current .................................................... 10

Measuring Electricity ............................................. 13

What Produces Magnetism? ................................. 14

Magnetism and Electric Currents ........................ 16

Producing Electricity ............................................. 17Steam ..................................................................... 19 Water ..................................................................... 19 Wind ...................................................................... 20

Delivering Electricity ............................................. 21

Electricity and Magnetism in Today’s World ............................................... 22

Glossary ................................................................... 23

Index ........................................................................ 24

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What Is Electricity?

You just learned that electricity can be produced naturally or by people. But what is electricity? It is a form of energy. Electrical energy comes from tiny, invisible particles called atoms. Atoms are the smallest bits of elements, the basic substances that make up all matter. Inside each atom are even smaller particles called protons, neutrons, and electrons.

Protons and neutrons make up an atom’s center, called the nucleus. Protons have a positive charge, while neutrons are neutral, meaning they have no charge. Electrons have a negative charge. Charges of the same kind—such as two positive charges—repel each other. Charges that are opposite—a positive and a negative charge— attract each other. PARTICLES HAVE CHARGES

In diagrams, protons have a + sign on them, and electrons have a – sign on them to show their charges. Neutrons have no label because they have no charge. This carbon atom has six electrons, six neutrons and six protons.

Electrons quickly orbit, or move in a circle around, an atom’s nucleus.

Because electrons and protons are drawn to one another, you might wonder why electrons don’t get pulled into the nucleus of an atom. They don’t because electrons whirl around the nucleus very quickly. Their high speed keeps them from crashing into it.

Normally, the number of positive protons and negative electrons in an atom is equal. Because the number of positive charges is equal to the number of negative charges, they cancel each other out. The atom is neutral, meaning it has no charge.

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electron

electron

proton

proton

neutron

neutron

ELECTRONS CIRCLE THE NUCLEUS

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The Two Kinds of Electricity

There are two kinds of electricity: static electricity and electric currents. They both involve the production and movement of charges. But they behave in very different ways.

Static Electricity

Static electricity is caused by a buildup of negative charges in one place and positive charges in another. When the attraction between the positive and negative charges becomes strong enough, the particles quickly stream back together.

Lightning is the most dramatic example of static electricity. In storm clouds, strong winds cause icy particles to collide violently. These collisions strip away many of the particles’ outer electrons, leaving the cloud full of positive ions and free electrons. The positive ions move to the top of the cloud. The electrons, which have a negative charge, collect at the base of the cloud. When the collections of positive and negative charges get large enough, they rapidly flow back together. As they do, the energy of their motion heats the surrounding air and creates a lightning flash. A lightning bolt heats the air around it to about 30,000°C (54,000°F). That’s five times as hot as the surface of the Sun!

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Atoms can gain or lose electrons by contacting other atoms. If an atom gains electrons, it acquires a negative charge because the electrons outnumber the protons. If an atom loses electrons, the protons outnumber the electrons, so the atom has a positive charge. An atom that has a charge is called an ion. An atom that has more electrons than protons is a negative ion. An atom with more protons than electrons is a positive ion.

It is important to remember that charges do not exist by themselves. A charge is always connected to a particle. Negative charges are carried by either electrons or negatively charged ions. Positive charges are carried by protons or positively charged ions.

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Positive Ion

Negative Ion

Positive ions have more protons than electrons.

Negative ions have more electrons than protons.

electron

proton

neutron

POSITIVE AND NEGATIVE IONS

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Sometimes the ground and the clouds have strong opposite charges. When this happens, an electrical charge flows between the cloud and the ground. This charge creates the lightning bolts that strike buildings and trees.

You can make a mini lightning bolt by scuffing your shoes on a carpet when the air is dry. Your body will pick up electrons from the carpet, gaining negative charge. If you put your finger near an object that has a neutral or positive charge, a spark will jump from your finger.

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Lightning that strikes the ground actually starts as a flow of charge from the ground up to the cloud.

Rubbing a balloon on your hair can create a similar effect as shoes on a carpet.

Electric Current

An electric current is the movement of electrons through matter. Materials that easily transmit an electric current are called conductors. The atoms of a conductor have electrons that are loosely attached and can move to other atoms. That movement of electrons becomes the electric current. Metals are the best conductors. Most wires that are used to carry an electric current are made of copper.

Materials that do not conduct electricity are called insulators. The outer electrons of an insulator are tightly bound to the atoms, so they don’t help electric currents flow. Rubber and plastic are both good insulators. Most electrical wires are encased in rubber to prevent the current from leaving the wire and causing a shock.

insulators

insulators

conductors

conductors

Some tools have plastic or rubber handles to prevent electric shocks.

Just as there are two kinds of electricity, there are two kinds of current. They are called direct current (DC) and alternating current (AC). Batteries use DC. The wall outlets in your home use AC. The electrons in a DC circuit always move in the same direction. The electrons in an AC circuit move rapidly back and forth.

The energy carried by electrons makes a lightbulb glow, causes an electric oven to heat, and makes fan blades turn. DC electrons move through a wire. But the electrons in an AC circuit don’t go anywhere. Instead, they just vibrate rapidly in one place.

In both kinds of current, the movement of electrons creates a flow of electrical energy that moves very quickly. When an electric current begins to flow in a circuit, energy fills the entire circuit almost instantly. As a result, a lamp lights up the instant you flip a switch.

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An electric current pushes against a force called resistance. The more resistance a circuit has, the more electrical energy is lost by changing into heat energy. Some electronics get hot when they’re on. That’s mostly due to resistance in the circuits inside.

An electric current needs a complete path in which to move. This path is called a circuit. If any part of a circuit is broken, the current stops flowing. A circuit needs to be made of a good conductor, such as metal wire.

alternating current

direct current

closed circuit

open circuit

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Measuring Electricity

Electrons don’t just move through a circuit by themselves. To get electrons moving, they need a kind of push. This push is called voltage. Voltage is measured in units called volts. In most cases, the greater the number of volts in an energy source, the greater the push and flow of energy. Most flashlight batteries have a voltage of just 1.5 volts. Car batteries produce 12 volts. House wiring carries about 120 volts of electricity.

The movement of electricity through a circuit is measured in units called amperes, or amps for short. The more electrons that are in motion in a wire, the higher the amperage.

Another common measure used in electricity is the watt. It is a measure of the rate at which electrical energy is being used.

1.5 volts

9 volts

Batteries and outlets have different volt levels that reflect how much power they can deliver.

Some metals, such as iron, can be magnetized. A magnetic field forms around the magnet.

12 volts

non-magnetized

magnetized

220 volts / 110 volts

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What Produces Magnetism?

As you learned earlier, electricity and magnetism are closely related. They are the two parts of a force called electromagnetism. Electrons spin like tops, and they are surrounded by a magnetic field. In certain metals, such as iron, the spinning electrons turn each atom into a tiny magnet. Those atoms can be made to line up in the same direction. When this happens, the entire piece of iron becomes magnetic. The more atoms that line up in the same way inside a piece of iron, the more powerful the magnet will be.

All magnets have a north and a south pole. Even if you cut a bar magnet into two magnets, each magnet will have a north and south pole.

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A magnet’s poles behave like positive and negative charges. Two south or two north poles repel each other, just as two positive or two negative charges repel each other. But the north poles and the south poles of two magnets are attracted to each other, just as a negative charge is attracted to a positive charge. If you have experimented with a pair of bar magnets, you have probably noticed this effect. In some positions they attract each other, and in other positions they repel each other.

Opposite poles attract. Like poles repel.

Magnetism and Electric Currents

A magnet can be made using electricity and a piece of iron. This type of magnet is called an electromagnet. A wire carrying current has a small magnetic field around it. When a coil of wire is wrapped around a piece of iron and an electric current is passed through the wire, the iron becomes a magnet. This happens because the coils create a magnetic field around the piece of iron, turning it into a magnet.

The strength of an electromagnet varies with the size of the piece of iron and the amount of current flowing through the wire. Electromagnets can be small enough to hold in your hand—or big enough to lift a car!

An electromagnet is a temporary magnet. It is magnetic only when an electric current is passing through the wire. People use electromagnets when they want to be able to turn a magnet on and off. The magnets you use in school are probably permanent magnets. Their magnetism is always on.

You can see a magnet’s field when you place the magnet under a piece of paper and sprinkle iron filings around it. The iron filings arrange themselves along the field’s lines of force. lines of force

What will happen to the paper clips if the wire pulls away from the battery?

N N N

NS S S

S

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Producing Electricity

Now you know how electricity can be used to make a magnet. But did you know that magnets can also be used to make electricity? Scientists studying magnets learned how to do this in the 1800s. They discovered that if a coil of wire is moved through a magnetic field, an electric current flows through the wire. The same thing happens in reverse when a magnet is moved through a coil of wire.

Scientists used what they learned about the relationship between magnetism and electricity to build machines called electrical generators. Cities, once mostly dark at night, became bright with electric lighting. Today, generators with large, powerful magnets spinning inside giant coils of wire are used to produce electricity. This important form of energy powers homes, offices, and factories.

Nikola Tesla supported using AC current to deliver electricity over long distances. He also helped invent radios.

These generators inside a dam use water to spin giant magnets.

The electricity used in homes, offices, and industry is produced at power plants. The plants use huge generators to produce AC electricity. These generators can be more than 15 meters (50 ft.) long (about the width of a basketball court) and weigh many tons. In most power-plant generators, large electromagnets spin inside coils of copper wire.

What causes the magnets to spin inside a generator? One of three main sources moves the magnets: steam, rushing water, or wind. Most power plants use steam produced by heating water to very high temperatures under a lot of pressure.

A dam creates a large lake behind it. In a hydroelectric plant, water flows through openings at the base of the dam. The rushing water spins the blades of turbines, which are connected to magnets inside wire coils in a generator.

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Steam

Power plants can produce heat to make steam in several ways. Three of the most widely used methods are:

• boiling water by burning coal, oil, or natural gas

• splitting uranium atoms, which releases large amounts of energy bound up in the atoms. The energy is then used to produce heat. Plants that use uranium to produce heat are called nuclear power plants.

• capturing focused sunlight to heat water. These power plants are called solar power plants.

The steam produced in power plants is used to spin large fanlike blades in a machine called a turbine. The turbine is connected to the magnets in a generator. As the turbine blades spin, they cause the magnets to spin inside coils of wire to produce electricity.

Water

Some power plants are part of large dams. These plants are called hydroelectric plants (hydro- comes from Latin and means “water”).

The largest dam in the world is the Three Gorges Dam in China. This hydroelectric dam is 185 meters (606 ft.) high and 2,335 meters (7,660 ft.) wide.

Wind

The power of wind can also be used to turn turbines that are attached to generators. Wind turbines, which look like huge airplane propellers, transfer their energy to a generator.

The blades of some wind turbines are as long as a truck.

Electricity and Magnetism in Today’s World

For thousands of years, people got along without using electricity. Work was done with muscle power. Candles and oil lamps provided light. During that time, magnetism was just a curious feature found in certain rocks, called lodestones. Lightning was a mystery. No one understood electricity, let alone the relationship between electricity and magnetism.

But today, electricity and magnetism, and their relationship, are well understood. Magnetism is widely used. As you just learned, large magnets are used at power plants to generate electricity. Magnets are also used in computer hard drives, electric motors, stereo speakers, credit cards, and other devices. Our understanding of electricity and magnetism has allowed us to create huge amounts of electric current to power all the things we use in our everyday lives. In fact, it is hard to imagine life without electricity. Electricity powers almost everything in our homes and businesses. Even many automobiles now use electric motors. More than ever, modern society is dependent on electrical energy.

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Delivering Electricity

The AC electricity produced at a power plant is carried away by large cables called transmission lines. The lines are strung between tall metal towers.

When the current leaves the power plant, a large device called a transformer increases the voltage to as high as 765,000 volts! All these volts are used to “push” electricity long distances through transmission lines. But before the current can be used in homes and factories, the voltage must be reduced. Another kind of transformer, far from the power station, lowers the voltage to a safe level before it enters homes, factories, and offices. In the United States, the voltage in homes and businesses is delivered at around 120 or 220 volts. In other countries, it is often delivered at around 220 volts.

Large cables called power lines can carry electricity hundreds of miles to transformers that reduce the voltage for use.

All cars use magnets and electricity. Some use electricity instead of gas.

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Glossary

alternating an electric current in which current (AC) electrons move rapidly back

and forth (p. 12)

amperes (amps) a measure of the amount of current in a wire (p. 13)

atoms the smallest parts of an element (p. 5)

charge the property of matter that causes it to be electrically positive or negative, caused by losing or gaining electrons (p. 5)

circuit a closed path along which an electric current travels (p. 11)

conductors materials, usually metals, that transmit electricity (p. 10)

direct an electric current in which electrons current (DC) move in one direction (p. 12)

electric currents the movement of electrons through matter (p. 8)

electricity a form of energy made when tiny parts move around in an atom; energy that can power many devices (p. 4)

electromagnet a magnet that can be turned on or off and is made by sending electricity through metal (p. 16)

electromagnetism a combined force of electricity and magnetism (p. 14)

electrons particles in an atom that orbit the nucleus and have a negative electrical charge (p. 5)

insulators materials, such as rubber and plastic, that do not transmit electricity (p. 10)

ion an atom that has gained or lost electrons and has an electrical charge (p. 7)

magnetic field an area around a magnet where magnetic force can be felt (p. 14)

magnetism a force that pushes and pulls certain metals (p. 4)

neutrons particles in the nucleus of an atom that have no electrical charge (p. 5)

protons particles in the nucleus of an atom that have a positive electrical charge (p. 5)

static electricity electricity caused by a buildup of negative charges in one place and positive charges in another (p. 8)

volts a measure of the amount of push that gets an electric current moving (p. 13)

watt a measure of the rate at which electrical energy is being used (p. 13)

Index

atoms, 5–7, 10, 14, 19 electrons, 5–10, 12–14 neutrons, 5–7 protons, 5–7generators, 17–20

lightning, 4, 8, 9, 22poles, 14, 15power plants, 18–22turbines, 19, 20