California science grade 5 (9)

Students know solar energy reaches Earth through radiation, mostly in the form of visible light... The electromagnetic spectrum, arranged from waves with the lowest amount of energy to w

L e s s o n 1

Electromagnetic Spectrum

6 PS 4 Many phenomena on Earth’s surface are

affected by the transfer of energy through radiation

and convection currents.

213

MAGAZINE ARTICLE

ELA R 6.2.2 Analyze text that uses the compare-and- contrast organizational pattern • ELA W 6.2.2 Write expository

compositions (e.g., description, explanation, comparison and contrast, problem and solution).

214

Write About It

Response to Literature In this article the author

tells about the invention of the laser How did this

invention come about? What impact has it had on

science? Write an essay comparing and contrasting

lasers and other forms of light What do they have in

common? How do they differ?

- Journal Write about it online

@www.macmillanmh.com

Most light, whether from a candle or a high-powered spotlight, is composed of many different colors and quickly spreads over a wide area as it travels away from its source Laser light, however, can

be concentrated into a very fine line which can travel thousands

of miles unless something blocks it

Lasers, invented in the early 1950s, have revolutionized

communications, astronomy, surgery, and a multitude of other scientific fields A laser is a specialized lamp producing light waves which are extremely bright, are pure in color, and can be highly focused

Light, television, and radio signals are all forms of

electromagnetic waves Microwaves, like those used to cook food in microwave ovens, are a few inches long Dr Charles Townes of New York’s Columbia University invented a way to amplify and transmit microwaves in 1954, calling it a maser, short for “microwave amplification by the stimulated emission of radiation.”

Lasers consist of four basic parts: an energy source, an active medium, an amplification system, and an output unit Many lasers are made using crystal rubies, but lasers also can be made using various gases and liquids Many recent laser designs incorporate the same kinds of semiconductor materials found in computer microchips As laser research continues and industry continues to develop new laser applications, lasers probably will come to play

an even greater role in our everyday lives

A Scientific Breakthrough

from MONKEYSHINES ON HEALTH AND SCIENCE

215

Electromagnetic Spectrum

Lesson 1

A rainbow appears when falling raindrops bend

sunlight Like a prism, each raindrop divides white

light into bands of different colors—the part of the

electromagnetic spectrum people can see There are

other parts that people cannot see Parts of the

electromagnetic spectrum warm the air on a hot day

6 PS 3.d Students know heat energy is also transferred between objects by radiation (radiation can travel through space) • 6 ES 4.b Students know solar energy reaches Earth through radiation, mostly in the form of visible light.

216

ENGAGE

• 3 medium-size jars

• black construction paper

Which material—white paper, black construction

paper, or aluminum foil—will most quickly raise

the temperature of water when placed in direct

sunlight? Write your answer as a prediction in the

form “If I wrap three jars using white paper, black

construction paper, and aluminum foil, then ”

Test Your Prediction

Experiment Fill three jars with the same

amount of water Wrap one of the materials

around each jar, and secure each with a piece

of tape Place the jars on a level surface

in a location that receives direct sunlight.

Place a thermometer in each jar, and stir the water

Record the temperature of the water in each jar

Wait 30 minutes, stir the water, and record the

temperature of the water in each jar again.

Draw Conclusions

Use Numbers For each jar, subtract the initial

temperature of the water from the temperature

recorded after 30 minutes in the sunlight

In which jar was the temperature of the water

most increased? Was your prediction correct?

Infer What caused the water temperature in the

jars to rise?

Set the jars in a place that does not receive direct

sunlight Which jar will lose the most heat? Wait 30

minutes, stir the water, and record the temperature

Which jar lost the most heat? Analyze the data and

present your results.

Step

Materials

Explore More

Step

6 IE 7.d Communicate the steps and results from an investigation

in written reports and oral presentations • 6 IE 7.e Recognize

whether evidence is consistent with a proposed explanation.

217

EXPLORE

▲ the colors of visible light

▶ Main Idea

Heat travels from the Sun

to Earth by radiation in the

is the distance along a wave before it repeats Shorter wavelengths have higher energy, while longer wavelengths have lower energy

The electromagnetic spectrum, arranged from waves with the lowest amount of energy to waves with the highest amount of energy, consists of radio waves, microwaves, infrared rays, visible light, ultraviolet light, X rays, and gamma rays Radio waves have the longest wavelengths and include transmissions of AM radio, shortwave radio, TV, and FM radio Microwaves, used

to power radar and satellite systems, as well

4W`ab

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Explore the elctromagnetic spectrum with

as ovens that cook food quickly, are

in the next part of the spectrum

Infrared rays, which people feel as

heat, are given off by the Sun and other

sources, such as active volcanoes Some

restaurants use infrared lamps to keep

food warm

In the middle of the spectrum are

the wavelengths of visible light We see

these wavelengths as colors that range

from red to violet

The next part of the spectrum

includes ultraviolet light waves

Ultraviolet waves carry more energy

than visible light waves Overexposure

to ultraviolet rays and other high-energy

waves can be harmful to humans After

ultraviolet rays are X rays and gamma

rays Gamma rays have very short

The Electromagnetic Spectrum

Which has a wider range of frequencies: visible light or radio waves?

Clue: Compare the ranges of the frequencies.

Reading Diagrams

Quick Check

Sequencing How are the forms of

electromagnetic radiation arranged from lowest energy to highest energy?

Critical Thinking Compare the

characteristics of radio waves and gamma rays

wavelengths and carry so much energy that they can even pass through metals and concrete

219 EXPLAIN

How does electromagnetic

radiation reach Earth?

Electromagnetic waves travel

about 150 million kilometers

(93 million miles) to reach Earth

from the Sun There is no air in

the empty space between Earth’s

atmosphere and the Sun Without

air, there is no substance for

waves to travel through How do

electromagnetic waves reach Earth?

The answer is that they travel by

radiation Radiation is the transfer of

energy by electromagnetic waves The

energy given off by the Sun is called

radiant energy It does not require two

objects to be touching, as conduction

does Nor does it require that the

objects be joined by a liquid or a gas,

as convection does

The light produced by the Sun is

the most common example of radiation,

but all objects give off a wide range

of electromagnetic waves The strength

of each type of radiation depends on

the temperature of the object

Absorption and Emission

of Radiant Energy

When radiant energy falls on an object, part of it is reflected, and part of

it is absorbed Absorption is the process

of taking in radiant energy A perfect absorber of electromagnetic radiation appears black, because it absorbs all colors of visible light as well as other types of radiation Objects that appear dark absorb some electromagnetic radiation, while objects that appear white or light-colored reflect more radiation than they absorb That is why the jar you wrapped in black paper in the Explore activity heated the water to a higher temperature.You might notice that dark objects absorb more radiant energy if, on a hot day, you touch a black metal surface such as a car The surface will feel hotter than a white metal surface It has absorbed more infrared radiation, which people feel as heat energy

▲ The International Space Station collects solar radiation to make electricity.

220

EXPLAIN

Emission is the process of giving

off absorbed electromagnetic waves

A good absorber is also a good emitter

Therefore a black, metal object takes

in more electromagnetic radiation, but

it also emits more This means that once

a dark object is away from the source

of radiation, it will cool off faster than

a similar, light-colored object

Solar radiation is the electromagnetic

radiation emitted by the Sun With

a surface temperature of about 5,500°C

to 6,000°C (9,900°F to 11,000°F),

the Sun emits a great amount of

high-energy, short-wavelength radiation

Most of it lies in the visible and

near-visible, or infrared, parts of the

electromagnetic spectrum A small

percentage falls in the ultraviolet range

of the spectrum

As the Sun’s incoming energy passes

through Earth’s atmosphere, it may

be absorbed, reflected, or scattered

Air molecules, water vapor, clouds, dust, and pollutants play a role in this process

Wavelengths of visible light are not greatly absorbed by anything

in the atmosphere, so they are able

to reach Earth’s surface Each visible color has its own properties and scatters differently For example, blue light, which has a shorter wavelength,

is scattered more easily than red or yellow light This is why the sky looks blue and the Sun looks yellow

Quick Check

Sequencing What events lead

up to the emission of radiation from an object?

Critical Thinking Why might

light-colored clothing be more suitable than dark-colored clothing in hot weather?

Absorption and Emission

Why do you think the hot desert air cools quickly at night?

Clue: What is the difference between the two photographs?

Reading Photos

221 EXPLAIN

What forms of radiation are useful?

heat at the same rate This is why you have to stir some foods to distribute the heat

High-energy radiation falls at the short-wavelength end of the electromagnetic spectrum This type

of radiation has extremely high energy High-energy radiation has the power

to generate electricity, kill cancer cells, and drive manufacturing processes

Radiation in the electromagnetic

spectrum can be divided into two

categories: ionizing radiation and

non-ionizing radiation Non-ionizing

radiation falls at the long-wavelength

end of the spectrum Every time you

use a microwave oven, you see

non-ionizing radiation at work Microwave

energy shakes the water molecules in

beverages and foods, creating friction

The friction caused by the moving water

molecules heats the beverage or food

In a microwave oven, all foods do not

infrared light

222

EXPLAIN

Electromagnetic radiation is

generally safe in small quantities

when used properly People can take

advantage of its properties for daily

tasks as well as special uses

Does a microwave oven use a higher or

lower frequency than an X-ray machine?

Clue: Look at the part of the spectrum

where microwaves and X rays are marked.

Reading Diagrams

Distance and Energy

What happens to the light beam from a flashlight as you move the flashlight farther from a piece

of paper? Tape a sheet of graph

paper to the wall, and write an x

in the middle of the paper.

Measure Hold a flashlight 2 centimeters away from the paper

Turn on the light, and keep the x

in the middle of the beam Trace

a circle around the spot of light Count and record the number of squares inside the circle.

Predict What will happen to the size of the circle if you move the flashlight to 4 centimeters and then 8 centimeters from the paper? How will this affect the brightness of the light and the size of the circle? Why?

Infer How does distance from the light source affect the amount of energy each square receives?

Infer If a planet were twice as far from the Sun as Earth is, would it receive half as much energy from the Sun as Earth does? Explain What effect would this have on the planet’s temperature?

Quick Check

Sequencing Explain how a

microwave oven heats food

Critical Thinking Why do you

think that the ionizing radiation

used for cancer treatment has to

be administered in small doses?

ionizing radiation

X rays

223 EXPLAIN

What forms of radiation are harmful?

blood cells that help the body fight off infections However, small doses

of X rays are not considered harmful

A chest X ray exposes a person to about the same level of radiation as

he or she would get while flying across the United States in a jet plane

Gamma rays are very frequency, high-energy waves that are given off by nuclear explosions and in nature by radioactive elements such as uranium Gamma rays have enough energy to pass through several centimeters of solid lead, and they are very dangerous to living cells

high-Quick Check

Sequencing How can becoming

sunburned lead to skin cancer?

Critical Thinking Why do you think

dentists make you wear lead aprons when they take X rays of your teeth?

Scientists take many precautions when they work with gamma rays.

Although radiation is used by

people in many ways, large quantities

of certain types of radiation can cause

harm These types of radiation, which

include ultraviolet light, X rays, and

gamma rays, are the highest energy

on the electromagnetic spectrum

Ultraviolet rays from the Sun can

cause suntans and sunburns Ultraviolet

rays cause pigment-producing cells

in the skin to produce a brown color

In addition, the radiation damages the

DNA in skin cells This damage may

lead to skin cancer Ultraviolet radiation

also ages the skin and can harm the

eyes Children under the age of 18 are

at greater risk from ultraviolet radiation

because their skin is more sensitive

X rays, in large quantities, can

harm living tissue by damaging or

killing cells The effects can include

reddened or burned skin, eye damage,

cancer, and a reduction of the white

224

EXPLAIN

Exploratory Writing

Think about all the forms of radiation

that you have encountered Write a

paragraph explaining the positive and

negative effects of radiation on your life.

Evaluate Limited Resource

Find out how the use of the radio-wave part of the electromagnetic spectrum

is managed and regulated and why this

is important.

Social Studies Link

Writing Link

Think, Talk, and Write

Main Idea How does solar energy reach Earth?

Vocabulary The transfer of energy by electromagnetic waves is

Sequencing What happens to the Sun’s incoming energy as it passes through Earth’s atmosphere?

The electromagnetic

spectrum is the

wide range of electromagnetic radiation organized

by wavelength

(pp 218–219)

Unlike conduction and convection,

radiation can travel

through empty space.

(pp 220–221)

Small amounts of

ionizing radiation are

useful for medical and energy needs.

(pp 222–223)

Make a

Study Guide

Make a half-book (see pp 487–490) Use

the title shown On the inside of the fold,

write two sentences about the main idea

of the topic.

Critical Thinking Provide arguments against the common misunderstanding that all radiation is harmful.

Test Practice Which of the following types of radiation is used for

- Review Summaries and quizzes online @www.macmillanmh.com

Summarize the Main Idea

225 EVALUATE

Form a Hypothesis

The Sun emits a huge amount of

electromagnetic radiation, including

wavelengths we can see and some we cannot

Waves with shorter wavelengths have higher

energy Scientists use information like this that

they read, as well as the results of experiments

they do, to help them form a hypothesis, or

make an educated guess, about something

Then they read more, experiment more, and

a glass prism, 4 thermometers, and a watch or a clock.

▶ Tape white paper in the bottom of the box Attach the prism

to one top edge of the box Place the box by a window so sunlight shines through the prism to make a spectrum Tape the thermometers in the box so you can read the numbers Tape one on the blue band of the spectrum, one on the yellow band, one just beyond the red band, and one in a shaded area Form a hypothesis about which thermometer will register the highest temperature and what the order of the readings will

be, from highest to lowest Record your hypothesis on a chart like the one on page 227 Wait 1 minute, and then read each thermometer Record the results on your chart Continue to read the thermometers at 1-minute intervals for a total of 6 minutes, and record the data.

226

EXTEND

▶ Now use your data to answer these questions What part

of the spectrum emits the most heat? What is the order of

temperatures, from highest to lowest? Do your data support

your hypothesis?

Apply It

▶ Would the temperatures in this kind of experiment be the same if

the box were lined with black paper? With aluminum foil? If you

used a desk lamp instead of sunlight? If you had a deeper box?

▶ Choose one of these variables, or make up one of your own,

and form a hypothesis about what you believe would happen.

▶ Then test your idea, and record the results to either support or

disprove your hypothesis.

6 IE 7.a Develop a hypothesis.

227 EXTEND

Lesson 2

Solar Radiation

The Sun is the major source of energy for

life on Earth How does that energy

affect life on Earth?

6 ES 4.a Students know the sun is the major source of energy for phenomena on Earth’s surface; it powers winds, ocean currents, and the water cycle • 6 ES 4.b Students know solar energy reaches Earth through radiation, mostly in the form of visible light.

228

ENGAGE

How can light energy

create motion?

Form a Hypothesis

A radiometer spins when exposed to sunlight What

do you think will happen if it is exposed to different

sources of light? Write your answer as a hypothesis

in the form “If a radiometer is exposed to different

light sources, then ”

Test Your Hypothesis

Place the radiometer in bright, natural sunlight

Record your observations.

Try using different light sources and light

sources with different intensities Record your

observations Does the radiometer speed up,

slow down, or stay the same?

Place a black cloth over the radiometer Look

underneath and observe the vanes Record

your observations

Draw Conclusions

Analyze How would you explain what you

observed?

Did your observations support your hypothesis?

Infer Do you think there is air inside the

radiometer? Why or why not?

How do you think the motion of the radiometer would

change if it were placed in direct sunlight for a whole

day? Form a hypothesis and test it Then analyze and

present your results.

6 IE 7.a Develop a hypothesis • 6 IE 7.b Select and use appropriate tools

and technology (including calculators, computers, balances, spring scales,

microscopes, and binoculars) to perform tests, collect data, and display data.

229 EXPLORE

How is the Sun an important energy source?

At any given moment, the Sun is shining on some part of Earth’s surface Sunlight warms the surface of the planet The heat from the Sun causes air currents and water currents to form

On Earth, living things use the Sun’s energy to carry out everyday functions

Energy from the Sun

▶ Main Idea

Almost all energy on Earth

comes from the Sun in the

4% reflected from Earth’s surface

15% absorbed by the atmosphere

25% reflected

by clouds

6% reflected by the atmosphere

6 ES 4.a

6 ES 4.b

230

EXPLAIN

▲ Plants use energy from the Sun to carry out photosynthesis and to produce food Animals, such as this giraffe, take

in some of this energy when they eat.

Solar Radiation

Energy from the Sun that

shines on Earth’s surface is called

solar radiation Plants use it to carry

out photosynthesis They convert solar

radiation to chemical energy, which

can be used by other organisms This

energy is passed along the food chain

When a plant or animal dies, the

energy it contains becomes food for

decomposers or in time, it may become

a fossil fuel

Solar radiation helped create fossil

fuels such as coal, oil, and natural gas

These fuels were formed from plant

and animal remains buried under

layers of mud and other materials The

plants and animals contained stored

energy from the Sun Over millions of

years, heat and pressure turned this

stored energy into fossil fuels that we

use today

Energy from the Sun also affects

nonliving things For example, uneven

heating of Earth’s surface causes winds

and contributes to ocean currents

Solar energy drives the water cycle

and influences a region’s weather and

climate All of these factors determine

the kinds of organisms that live in

the region

Quick Check

Summarize How do animals

obtain energy from the Sun?

Critical Thinking How did the

Sun’s energy become trapped

in fossil fuels?

231 EXPLAIN

▶ Solar radiation provides the energy to obtain salt from seawater at this salt-production facility.

How does the Sun

affect the water cycle?

Solar radiation powers the water cycle,

or the movement of water between Earth’s

surface and the air Energy from the Sun

helps recycle Earth’s supply of water, which

is essential to life

The main processes that occur during the water cycle

are evaporation, condensation, and precipitation During

evaporation, solar radiation warms the water on Earth’s

surface The water molecules absorb energy from the Sun and

move faster Then the molecules near the surface of the water

escape into the atmosphere as water vapor

Evaporation of water from Earth’s surface requires a great

deal of energy More than 70% of Earth’s surface is covered

by oceans, so an enormous amount of water vapor rises into

the atmosphere every day The Sun supplies the energy for all

of this evaporation

Solar Energy and the Water Cycle

What happens after water vapor condenses?

Clue: Follow the arrows to trace the path through this cycle.

Reading Diagrams

Watch solar energy and the water cycle

@ www.macmillanmh.com

232

EXPLAIN

Solar Still

You can use the Sun’s energy to separate a solution of salt and water Make a saltwater solution

by dissolving 2 tablespoons of salt per cup of fresh water Fill a large bowl with salt water to a depth

of about 2 inches.

Place an empty glass in the center

of the bowl The top of the glass should be below the edge of the bowl but above the surface of the salt water.

Cover the bowl with plastic wrap Use tape, if necessary, to make

a tight seal.

Place a heavy object, such as a rock, in the center of the plastic wrap over the glass.

Leave the still in direct sunlight for a few hours Then remove the plastic wrap Has water collected

in the glass?

Predict Do you think the water

in the glass is salty or fresh?

Why? How would you test your prediction?

Sequence Explain the role of evaporation and condensation

in transferring water to the glass.

Temperatures in the atmosphere are

cooler than those at Earth’s surface,

because the atmosphere absorbs less of

the Sun’s energy than the surface does

With less energy from the Sun available,

the water molecules in the atmosphere

slow down They begin to change from

water vapor into liquid water The

molecules collide and join together as

drops of water through condensation,

and in time they form a cloud

When enough water accumulates in

a cloud, the water falls as precipitation

Depending on the air temperature, the

precipitation may take the form of rain,

sleet, snow, or hail Precipitation provides

water for living things and fills Earth’s

oceans, lakes, rivers, and streams

Quick Check

Summarize What happens to water

molecules in the air after they have

cooled due to a loss of energy?

Critical Thinking What part of the

water cycle does solar radiation

affect most directly?

233 EXPLAIN

Ac\¸a`Oga

How does the Sun affect

climate and weather?

The Sun is the major source of

heat energy for Earth Earth’s surface

absorbs heat from sunlight, and the

surface heats the air above it The

amount of heat energy that reaches

Earth in a place affects the area’s

climate and weather

How have the penguins adapted to life in a

region that receives limited solar radiation?

Clue: Look at the pictures of the penguins

and the camel How do these animals differ?

Reading Diagrams

Climate

Climate is influenced by factors such as temperature, precipitation, wind, mountain ranges, ocean currents, latitude, and altitude Energy from the Sun affects a region’s climate in a variety of ways It warms the air, land, and oceans, and it helps determine patterns of precipitation, wind, and ocean currents

Solar Radiation and Climate

234

EXPLAIN

Sunlight does not strike Earth’s

surface at the same angle at all times or

in all places It shines more directly at

the equator and more indirectly at the

poles Areas near the equator receive

the most heat energy from the Sun and

generally have warm climates Closer to

the poles, the Sun’s rays strike Earth at

a low angle, spreading their energy over

a large area and creating a cool climate

To see how this works, shine a

flashlight at a sheet of graph paper

Move the light upward from a low

angle to the paper until it is directly

above the paper Notice that fewer

squares are lit as you move the

flashlight upward In the same way,

when light from the Sun strikes

Earth at a higher angle, the energy

is concentrated in a smaller area

Weather

Weather is the state of the

atmosphere at a given place and

time The local conditions that make

up weather are air temperature, air

pressure, humidity, wind, clouds,

and precipitation All of these elements

are connected to the Sun’s energy

For example, humidity, clouds, rain,

and snow result from evaporation,

which is caused by solar radiation

Air pressure is the force put on an

area by the weight of the air above it

Air pressure depends on the density of

the air As air is heated by the Sun, the

molecules in the air move faster and

move farther apart from one another

For this reason the heated air becomes

less dense and exerts less pressure on

Earth’s surface

Differences in air pressure are also the cause of wind, or moving air Air moves from areas of high pressure to areas of low pressure By determining air pressure, heat energy from the Sun also affects wind patterns Winds, in turn, drive the currents on the surfaces

of Earth’s oceans

dry weather

wet weather

Quick Check

Summarize How does the angle at

which the Sun’s rays strike Earth’s surface affect climate?

Critical Thinking What type of

weather often follows an increase

in air temperature?

235 EXPLAIN

How does Earth gain

and lose energy?

Almost all the heat on Earth comes

from the Sun Earth also gives off,

or radiates, heat into space If Earth

were not able to give off some of the

energy from the Sun, the planet would

be too hot for life When the balance

of heat energy is maintained, Earth’s

average surface temperature remains

about 14°C (59°F) A disruption in

the balance can cause the average

temperature to rise or fall

The atmosphere plays an important

role in maintaining the balance of

heat energy on Earth When the Sun’s

energy reaches the atmosphere, part of

it is reflected back into space by water

droplets in clouds and dust particles

Another part is absorbed by water vapor

in the atmosphere Only about half of

incoming heat energy reaches Earth’s

surface and is absorbed by it

Different materials on Earth absorb energy differently Dark-colored objects become hotter than light-colored objects when exposed to the same amount of sunlight This is why, on a hot day, people might walk barefoot comfortably over a concrete sidewalk but hop painfully over a black, asphalt driveway

The ocean and the land also absorb heat energy differently Water heats up and cools down more slowly than land, because it takes more heat to raise the temperature of water than it takes

to raise the temperature of land The resulting differences in temperature influence weather and climate

◀ Even on a warm day, ocean water can be cool.

Quick Check

Summarize What happens after

the Sun’s energy reaches Earth’s atmosphere?

Critical Thinking Explain how

water vapor in the atmosphere keeps Earth’s surface warm

236

EXPLAIN