Invisible pull electricity and magnets

2024-07-28 作者:

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United States of America and/or other d in the United States of AmericaISBN 0-15-366668-41 2 3 4 5 6 7 8 9 10 039 10 09 08 07 06 05Static Electricity ...........................................

2Current Electricity .........................................

4Conductors and Insulators ...............................

6Magnetism ................................................. 8Uses of Magnets ...........................................10Combining Magnets and Electricity ....................12Electricity from Magnets .................................14Glossary .....................................................16

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Static ElectricityEvery day, you turn on lights in your home. In

winter, you may turn on the heat. You depend on

a refrigerator to keep your food cold. Maybe you

heat food in a microwave oven. All of these tasks

are possible because of electricity.

Electricity

is a

form of energy produced by moving electricity is a kind of electricity that forms

when an electric charge builds up in an object. It

can even build up in a person. It can make your

hair stand straight t electricity, it

would be hard to light

your house.2When electricity builds

up in a cloud, it comes

out as ing is also a form

of static electricity. It occurs

when electricity builds up

in a cloud. The electricity

comes out of the cloud

as a bolt of lightning. The

lightning releases so much

energy that you can hear thunder even from far away.

MAIN IDEA AND DETAILS

What might make your hair stand straight up?

Benjamin Franklin

discovered that lightning

is a form of electricity.

He tied a metal key to a

kite in a storm. Franklin

saw a spark jump from

the key and knew that

it had been caused

by lightning!3

Current ElectricityElectricity that moves through a wire is called

current electricity. When you plug in a lamp, you

are connecting the lamp to a wire hidden in the

wall. That wire carries current electricity.A

circuit is a path that electricity flows through.

The bulb in a lamp lights up when there is a

complete circuit for the electric current to follow

from the wall to the bulb.

The TV and DVD

player depend on

current electricity

to make them work.4Electricity is even

used appliances in your home depend on

electricity. You use current electricity to power

objects that are plugged in. Suppose you plug in

a TV. Current electricity moves from wires in the

wall to the TV’s plug and then into the TV itself. The current electricity powers the TV.

Items that are not in the home use current

electricity, too. Signs on the outside of buildings, traffic lights, and cars all use current electricity.

MAIN IDEA AND DETAILS What makes plugged in appliances run?

5

6Conductors and InsulatorsThere are some things that electricity can move

through easily. These things are called conductors.

For example, electricity moves easily through

metal. The wires that current electricity travels

through are often made of copper, which is

a very good reel contains copper

wire, which is often used

to carry metal threads in this

wire carry electricity. The

covering wrapped around

them is an things block electricity and do not

allow it to pass through. These things are

called insulators.

Plastic and rubber make good insulators. That is

why they are often used to cover wire. It can be

dangerous to touch a wire when it is carrying a

current. Insulators prevent you from getting hurt by blocking the electric current.

COMPARE AND CONTRAST How are conductors and insulators alike? How are they different?

7

MagnetismMagnets are made of a kind of metal that

attracts iron. Anything that attracts objects with

iron in them is

magnetic.

When a metal is attracted to a magnet, it can

stick to the magnet. A magnet can lift an object if

the attraction is strong.

Not all metals are attracted to magnets—only

those with iron.

These objects are

attracted to magnets.8Every magnet has both a

north pole and a south magnet has two ends, or poles. One end

is called the north pole, and the other is called

the south pole. The north pole of one magnet

attracts the south pole of another magnet. They stick together.

If you try to put the north pole of one magnet

near the north pole of another magnet, the magnets will push away, or repel, each other.

Opposite poles of magnets are attracted to each other. Like poles repel each other.

COMPARE AND CONTRAST What happens if you put the north poles of two magnets near each other? What

happens if you put the north pole of one magnet near the south pole of another?

9

Uses of MagnetsMagnets can be used in many ways. Small

magnets are used around the house to hold

papers on refrigerator doors and to keep cabinets

closed. You may have an electric can opener at

home that uses a magnet to hold the can in place.

There are many uses for

magnets. Some can be fun!

10Lodestone is a natural mineral

that acts as a magnet. It attracts

iron and was once used by sailors

to make a simple compass.A compass contains a

magnetic needle that is

attracted to Earth’s North

Pole. A compass can help

you figure out which way

you need to s are used in a lot of things we need

every day. These include computers, motors, and compasses.

MAIN IDEA AND DETAILS Name and describe ways that people use magnets every day.

11

12Combining Magnets and

ElectricitySome magnets are powered

by electricity. As long as the

electricity is on, the magnet

Magnets can work

attracts things with iron in

in different places.

them. When the electricity is

They can be used

turned off, the magnet stops

underwater or on

working. These magnets are

the moon!called electromagnets.

Electromagnets are very

helpful when you need to move

something very heavy. When the

electricity is on, you can lift the

object easily. When you turn the

electricity off, you can remove

the object from the magnet

without having to pull.

This ordinary screw

can become an

electromagnet

if wire containing

electric current is

wrapped around giant electromagnet

lifts large omagnets are very useful to builders.

Workers can use an electromagnet to lift a huge,

metal beam into place. Then, when the beam is in

the right place, they turn off the electricity and the beam will stay put.

Large magnets can also be used to move cars

that no longer run and to separate iron from other scrap material for recycling.

COMPARE AND CONTRAST How is an electromagnet different from a regular magnet?

13

Electricity from MagnetsJust as electricity can make a magnet, a magnet

can make electricity. You can make electricity by

moving a magnet near a coil of wire so that

current electricity flows through the wire. A

machine that makes electricity this way is called

a generator.

Suppose that power lines near your house get

knocked down during a storm. You can’t get

electricity in your home. If you have your own

generator, you’ll be able to make your own

electricity—from a magnet.

MAIN IDEA AND DETAILS How are magnets used to generate electricity?

Generators are

perfect for making

electricity outdoors.14This globe is filled

with static y

Static electricity develops when an electrical

charge builds up in an object. Current electricity

travels through wires from one place to another.

Magnetic items attract objects with iron in them.

Electromagnets work only when electricity flows

through the magnet. Generators make electricity using magnets.

15

Glossarycircuit

(SER•kuht) A path that electricity follows

(4, 15)electricity (ee•lek•TRIS•ih•tee) A form of energy

produced by moving electrons (2, 3, 4, 5, 6, 7, 12,

13, 14, 15)magnetic (mag•NET•ik) Attracting objects that

have iron in them (8, 11, 15)16Think and Write

1.

Explain how electricity and magnetism can

work together.2.

COMPARE AND CONTRAST Compare static

electricity and current electricity.3.

MAIN IDEA AND DETAILS Would a very

large magnet be able to pick up a small tack

made of plastic? Explain.

4.

Narrative Writing Invent a machine that

uses an electromagnet, a generator, or a

motor. Write a paragraph explaining how your

machine works.

Hands-On ActivityMake your own magnet! Magnetism is a form of

energy. You can make it move from one object to

another. Rub an iron nail with a magnet until it, too,

becomes magnetic. Then, make a list of items you can

pick up with it.

School-Home ConnectionLook around your home tonight. What do you find

that uses electricity? Do you see any magnets? Share

your findings with the class.