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Year 9-10 General ScienceDisk Filename Topic Name12.Waves Wave Energy (inc. Light)13.Motion Forces & Motion14.Electricity Electricity15.Atoms Atoms & Elements16.Reactions Compounds & Reactions17.DNA Cell Division & DNA18.Evolution Evolution of Life19.Health Health & Reproduction20.Universe The Universe21.EarthScience Earth Science22.Resources Resources & Technology

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keep it simple science

Years 9-10 Topic 12 Wave Energycopyright 2008 keep it simple sciencewww.keepitsimplescience.com.au

3

Mind-Map Outline of TopicThis topic belongs to Physics, the study of energy, force and motion. In this topic you will study how energy moves in the form of waves,

then go on to study one very important wave type... light.

Properties& Uses

The WaveEquation

ColourTheEye

OpticalLenses

WaveMedium

Crests, Troughs& Amplitude

Absorption,Reflection,Refraction

Wave Energy

Waves CarryEnergy

LightWaves

Wavelength,Frequency& Speed

ElectromagneticWaves



4


Make your own Mind-Map TITLE PAGE.Cut out the boxes. Sort them into an appropriate lay-out on a page of your

workbook, then glue them down. Add connecting arrows and colour in.

Properties& Uses

The WaveEquation

Colour

TheEye

OpticalLensesWave

MediumCrests, Troughs

& Amplitude


Wave Energy

Waves CarryEnergy

LightWaves



Make your own Mind-Map TITLE PAGE.Cut out the boxes. Sort them into an appropriate lay-out on a page of your

workbook, then glue them down. Add connecting arrows and colour in.

Properties& Uses

The WaveEquation

Colour

TheEye

OpticalLensesWave

MediumCrests, Troughs

& Amplitude


Wave Energy

Waves CarryEnergy

LightWaves






5

Waves Carry EnergyMany types of energy are carried as waves.

Waves carry energy from one place to another.Only the energy moves... substances do NOT move from one place to another.

(A substance might vibrate as energy moves through, but it doesnt go anywhere.)

Examples of Energy Carried as WavesLight & Sound WavesWhen you see anything you aredetecting light waves carrying energy toyour eyes. Things that glow are emitting(giving out) light waves. Most thingsthat you see are not emitting light, butreflecting it to your eyes.

When you hear anything, you aredetecting sound waves.

In a lightning storm,the electricaldischarge emits lightwaves... so you seethe lightning flash. Italso creates soundwaves... so you hearthe thunder. The soundwaves travel moreslowly that the light,so you hear thethunder after you seethe lightning.

Water WavesThe energy of the wind blowing acrossthe oceans creates water waves.

Water waves can carry the energy forthousands of kilometres across anocean, until the waves break as theyapproach a coastline.

Before they break, the water doesntactually go anywhere. The water movesup and down as huge amounts ofenergy flow past, but the water itselfgoes nowhere.

Once the wave breaks, the water itselfsurges forward. Now you can catch it,and now its energy batters the coastcausing erosion and movement of sand.

What is Energy? (Revision) Energy is what causes things to change. There are many different types of energy. Here are just a few:

Type of Energy Changes Caused by this EnergyKinetic (in moving objects) Change in position because object is moving.Potential (stored) Only causes changes when released in another form.Heat Change in temperature. e.g. a stove causes food to get hot.Light Nerve changes in your eye which allow you to see things,

or chemical changes in the film in a camera.Sound Vibrations in your ear which allow you to hear.Electrical Energy Can cause a light bulb to glow and produce light,

or a stove element to get hot and produce heat.Radio Waves Can cause electrical vibrations in an antenna.

This allows reception of mobile phone, radio & TV programs.


6

Some Waves Need a MediumSome waves can only travel through substances.

The substance vibrates as the wave energy passes through.The substance is called the medium for the wave.

Without a medium, the wave cannot exist, and the energy cannot move.

Sound Needs a Medium

Some Waves Can Travel Through VacuumNot all waves need a medium to travel through.

Water waves in the ocean need the water as a medium.The shock waves of an earthquake need solid rock as their medium.

Electromagnetic WavesLight waves can (obviously) travelthrough empty space from the Sun toEarth.

Light does not need amedium to travelthrough.

Light can travel throughsome substances (suchas air, water & glass),but it actually travelsbest through a vacuum.

Light is an electromagnetic (EM) wave.The energy is transmitted by thevibration of electric and magnetic fields.

There is a whole family of other EMwaves which you will study later in thistopic.

The Speed of LightLight waves travel at the amazing speedof 300,000 kilometres per second.

Thats just over 3seconds to travel

1 million km.

Light covers thedistance from Sun to

Earth (150,000,000km) inabout 8 minutes. Our

fastest space vehicleswould take about 2

years to travel that far.

We have reason to believe that nothing canever travel faster than the speed of light.

We should call it the Speed of EMWaves because all EM waves travel atthis same speed.

When the bell-jar is filled with air, you canclearly hear the bell ringing.

When most of the air is pumped out, you canbarely hear it, but you can see that it is stillringing.

Sound cannot travel in a vacuum. It must have a medium.

Sound waves not only travel in air, but canmove through water or solids as well.



Your teacher might demonstrate this inclass.

Sealed, glass bell-jjarwith electric bell or

buzzer inside.

Air can bepumped out by avacuum pump, orallowed back inthrough a valve.


7

Science Rejects Theories That Dont WorkTo the scientists of the 18th and 19th centuries it seemed obvious that light waves

must travel through something... there must be a medium for light waves.All other types of waves which had been studied (e.g. sound & water waves)

needed a medium and could not travel in a vacuum.

Scientific Developments Lead to New TechnologiesIn the mid-19th century, scientists were not quite sure what light was. Earliertheories that light was a stream of particles had been discounted, so it was

generally agreed that light was a wave. But what kind?

The Theory of the AetherThe aether was thought to be a fluidwhich totally filled the Universe. It hadno mass and did not interact with solidobjects. For example, it had no effect onthe planets moving through space.

The only property of the aether was thatit allowed light waves to be propagatedthrough space.

In the second half of the 19th centurythe existence of the whole family ofelectromagnetic (EM) waves wasdiscovered. Light was just one type of awhole spectrum of EM waves travellingin the aether.

Scientists began experimenting toprove that the aether really existed.

The Michelson-Morley ExperimentThis famous experiment in 1887attempted to measure the interferencepatterns which theoretically shouldhave occurred under certain conditions,as light travelled in the aether.

The expected interference patterns didnot occur. The experiment was repeatedmany times, with greater precision eachtime. Same result... no aether effects.

Arguments went back-and-forth for 20 years,but it was finally settled by Albert Einstein in1905. His Theory of Relativity gave a new way tothink about light and how it travelled in space.There was no longer any need for an aether.

Soon, experiments to test Relativity gave clear,positive results and the aether was quietlyforgotten. This is how Science works.



James Clerk Maxwell (Scottish, 1831-79)In 1864, Maxwell published his theory ofElectromagnetic (EM) Waves.

He showed mathematically how a wavecould be made of fluctuating electricand magnetic fields and how it wouldspread out at the speed of light.

His equations alsosuggested that thereshould be a wholespectrum of EM waves atother wavelengths andfrequencies. The race wason to find them!

Radio Waves were discovered andstudied in 1880, and by 1895 the firstradio communications began. By the1930s the first pictures weretransmitted by radio signal (television)and radar was being developed.

In World War II, radar developedand extended into the

Microwave band. From there weget modern communication

networks (& microwave ovens).

In 1895, Wilhelm Rontgendiscovered X-Rays and by the

early 20th century they were usedfor medical imaging.

Maxwells new scientific theories led directly to many newtechnologies which are vital in todays society.


8

How Energy is Carried by a WaveTo understand how a wave carries energy it is best to start

with something familiar, such as waves in water.

Wave AmplitudeTo a surfer, how big the surf waves are is a very important thing.

In scientific terms, this is the wave amplitude.

Significance of Wave Amplitude

Water WavesIf you look at unbroken swell waves inwater, you will see that they are made upof a series of crests and troughs whichmove across the surface.

If you watch a boat as ocean swells goby, you will see that it simply moves upand down... it is not pushed along.

Only the energy travels. The water only oscillates up and down.

You cannot surfunbroken swells

because the wavewill not push youforward. You onlyfloat up and downon the crests and

troughs.

When the wave approaches shore itbegins to break.Now the waterbegins to tumbleforward and youcan catch it.

However, a brokenwave is NOT awave in thescientific sense.



Surfers tend to measure theheight of a wave as the

vertical distance from troughup to crest.

Notice that amplitude ismeasured from the flat water

surface up to the crest.

In a Sound Wave, the amplitudedetermines how loud the sound is... itsvolume.

When you turn up the volume, you areincreasing the amplitude of the soundwaves that you are hearing.

In a Light Wave, the amplitudedetermines the brightness of the light.

When you see 2 objects, but one isbrighter than the other, the difference isthe amplitude of the light waves whichare entering your eye.

Crest

Crest

Trough

Water surface if there were no waves

This distance is thewave amplitude

Trough

Floating boat moves up and downas waves go past.

Energy travelsacross surface


9

Fill in the blank spaces.

Waves carry a)......................... from oneplace to another.

Some waves require a substance, orb)............................., to travel through. Asthe wave moves, the particles in thesubstance c).............................., but theydo not d)................................ An exampleis e)............................ waves which cantravel in air, water or solids, but cannottravel through a f).............................

Other types of energy do not need ag)........................... to travel in. Forexample, h)........................... waves cantravel through a vacuum. They alsotravel through substances such as air,i)...................... or .............................

Light waves are just one type of afamily of waves called j).................... -................... waves. All of these travel ata speed of k)............................... km/hour.

Waves of any kind have certain featuresin common. A wave moves as a series ofl).................... (high points) andm)........................... (low points). In awater wave, the water itself simplymoves n)............................. as the energyflows by.

The o).................................. of a wave isthe distance from the average positionto a crest or trough. In a sound wave thisdetermines the p)........................... of thesound. With light waves this determinesthe q)................................... of the light.

Worksheet 1Waves Carry Energy Student Name.............................................

1.The diagrams show 3 different wavesdrawn to the same scale.

a) On wave P label the position of acrest and a trough.b) On wave Q draw an arrow to show thedistance you would measure for theamplitude of the wave.c) If these waves represent light waves,which one is the least bright?

2. A cork is floating on a calm pond. Thensomeone drops a rock in the water sothat a series of ripple waves moveacross the surface.Describe the movement of the cork asthe waves reach it and go past.

3. An astronaut on the Moon watches ashis partner hits a rock with a hammer.Explain why he can see it happen, butcannot hear the sound of it.

4.Suggest how the astronaut can talk tohis partner on the Moon.

Worksheet 2Wave Characteristics

Student Name.............................................



P

R

Q


10

Wavelength and FrequencyThese 2 measurements are very important to describe different waves.

Wavelength ()The wavelength is a measure of thedistance from one wave crest to the next.

Wavelength can also be measured fromone trough to the next.

The Greek letter lambda () is oftenused as the symbol for wavelength.

Since wavelength is a distance, it can bemeasured in cm, metres, km, etc.

Some Actual WavelengthsSome radio waves have a wavelength ofseveral kilometres. Light waves havewavelengths less than 1/1,000 of 1mm.

Ocean waves typically have wavelengthsof between 20m to 100m. Ripples in apond have wavelengths of a few cm.

Sound waves are typically a few cm inwavelength.

Frequency (f)Frequency measures how many wavesgo past per second. Symbol f is used.

It is very difficult to visualise this with adiagram. Your teacher mightdemonstrate frequency with a slinkyspring. (see below)

The unit of measurement is called thehertz (Hz) named after a great Germanscientist of the 19th century.

A frequency of 10Hz means that 10complete waves are going past eachsecond.

Some Actual FrequenciesOcean waves can have very lowfrequencies of only 0.1Hz, or less. Thismeans that only 1/10 of a wave passes in1 second. Another way to think of this,is that it takes 10 seconds (or more) forone complete wave to go by.

Sound waves have frequencies of 100sand 1,000s of Hz.

Light waves have frequencies measuredin billions of Hz.



The Relationship of Wavelength & FrequencyIf you shake one end of a slinky spring up and down,

you can set up a wave pattern.

Now shake it faster, and faster. You are increasing the frequency.Notice that the wavelength gets less as frequency gets higher.

wavelength

wavelength wavelength

wavelengthShake thespring ina regular

way

Shakefaster Even

faster

Wavepattern in

spring

ampl

itude

wavelength

Amplitudestays the

same


11

Speed, Wavelength & FrequencySpeed means how fast something moves.

The speed of any wave depends on both its wavelength and frequency.

The Wave EquationThere is a simple, mathematicalrelationship between the wavelength,the frequency and the speed of anywave.

SPEED = WAVELENGTH x FREQUENCY

v = x fv = velocity (speed), measured in

metres per second (m/s).

= wavelength, measured in metres (m).( is the Greek letter lambda)

f = frequency, measured in hertz (Hz).

Example CalculationA series of water waves measure 80cm(0.80m) from crest to crest. Eachsecond, 2.5 complete waves go past.What is the speed of the waves?

SolutionWavelength = 0.80m. Frequency = 2.5Hz.

v = x f= 0.80 x 2.5= 2.0

The speed of the waves is 2.0 m/s.

Note: If you used = 80cm, the answer would be200 cm/s. This is exactly the same, but indifferent units. You should try to use metres,and m/s whenever possible.



Worksheet 3Using the Wave Equation

1. A sound wave with a frequency of660Hz has a wavelength of 0.5m.What is the speed of the wave?

v = x f = ............ x ............= ....................

The speed of the wave is ................. m/s.

2. Another sound wave with a frequencyof 3,300Hz has a wavelength of 10cm(0.1m).What is the speed of the wave?

v = x f = ............ x ............= ....................


3. A water wave has a wavelength of 50m.A complete wave takes 20sec. to go by, soits frequency is 0.05Hz.What is the speed of the wave?

v = x f = ............ x ............= ....................


4. A wave in a slinky spring measures40cm (0.4m) from crest to crest. Thespring is being shaken up and down 3times per second. How fast does the wave travel?

5. A sound wave has a frequency1,000Hz. It is travelling in air at a speedof 330 m/s.What is its wavelength?

6. Sound travels much faster in waterthan in air... 1,500 m/s. What wavelengthwould the 1,000Hz sound wave have inwater?

Student Name.............................................




12

Electromagnetic (EM) WavesThe EM waves are a family of waves which all travel at the speed of light.

They have many important properties and uses.

Type of Wave

Radio

Microwaves

Infra-Red

Light

Ultra-Violet

X-Rays

Gamma Rays

Properties & UsesUsed for transmitting radioand TV programs & mobilephones. Also, communication forplanes, ships, military, etc.

Microwaves of some frequencies can cause food to get hot.

They are used in a microwave oven. Other frequencies are used in

communications, radar and GPS.

Infra-Red is heat radiation. Although we cannotsee it, we can feel it on our skin.

Light can be detected byour eyes, so to us it is themost important member ofthe EM family.

Photographic film and thelight detectors in digitalcameras are also sensitiveto light radiation.

Ultra-Violet (UV) rays are dangerous to livingthings. UV causes sunburn and can cause skincancers. Luckily, most of the UV coming from theSun is blocked by the ozone layer, high up in theatmosphere.

X-Rays are very penetrating andcan go straight through manythings. This is why they areused for medical imaging of

bones, and for detectingweapons, etc in airline luggage.Excessive doses of X-rays canbe very dangerous to people.

Gamma Rays are even morepenetrating than X-rays.They are given off by radio-active substances. They cancause cancer, but can alsokill cancer cells. They areused in radiation treatmentof cancer patients.

Wav

elen

gth

getti

ng s

hort

er

Freq

uenc

y ge

tting

hig

her

Long Wavelength,Low Frequency

Short Wavelength,High Frequency

Although we describe these as different types ofwave, they actually form a continuous

spectrum. The only difference from one typeto another is the frequency and wavelength.




13

1. A radio wave has a frequency of 50kHz(= 50,000 Hz) and wavelength of 6km.a) Write the frequency valuein scientific (or standard) notation. .........................b) Convert the wavelength to metres, and write it in standard notation. .........................c) Use the Wave Equation to calculatethe speed of the wave (in m/s).

V = x f = ...................... x.......................

= ................................... m/s(answer in standard notation)

2. A short wave radio signal has awavelength of only 80 cm. (= 0.8 m). Itsfrequency is 3.75x108 Hz.Calculate its speed.

3.Microwaves used in cooking have afrequency of 2.5x109 Hz. What is their wavelength?

V = x f, so = V / f

(answer in metres, and in cm)

4.A typical infra-red wave has awavelength of just 1/100 mm (= 1x10-5m).What is the frequency of this wave?

V = x f, so f = V /

Write the answer in standard notation, thenagain in normal decimal notation.

5.A wave of visible light has a frequencyof 6x1014 Hz.Find the wavelength (in m).

6. A wave of UV radiation has a wavelengthof 5x10-9 m. Find its frequency.

7. What is the frequency of an X-ray if itswavelength is 3x10-11 m?

8.What is the wavelength of gammaradiation if its frequency is 5x1021 Hz?

Worksheet 4The Wave Equation

(More Difficult Problems)These problems require the use of a scientific

calculator. You must be familiar with itsexponential function, and be able to work

with scientific notation for very large,and very small numbers.

Student Name.............................................

Remember, ALL EM waves travelat 3.0x108 m/s (= 300,000 km/sec)




14


All a)....................................... (EM) wavestravel at the same speed: the speed oflight which is b)....................... km/sec.They do not need a c)........................ andcan travel through a vacuum.

The EM waves with the longestwavelength (and d)............................frequency) are e)........................ waves.These are used to transmit signals forf)....................... and .................... as wellas mobile phones.

Microwaves have g).........................wavelength and h)............................frequency. They are also used incommunication as well as i)....................

j).................................. is heat radiation.we cannot see it, but can feel it on ourk)...........................

The next member of the EM family isl)........................... which is the only onethat we can m).......................

n).......................................... radiation cancause sunburn and skin cancer. Luckily,most of it is blocked by the o)..................layer of the atmosphere.

p).................. are used for medicalimaging because they can q).................................... many things including you.

r).................. rays are even morepenetrating. They are given off bys)...................................... substances.These waves have the t)...........................wavelength and u)..............................frequency of all the EM waves.

Worksheet 5EM Waves Student Name.............................................

1.Which 2 types of EM waves are used ina lot of our communications?

............................ and ...............................

2.Originally, the science of Astronomywas done with light waves... by eye andtelescope. Today, modern astronomersuse ALL the types of EM waves.What feature of all EM waves make themuseful for studying outer space?

3. At what speed do all EM waves travel?

4.Night-vision cameras use infra-reddetectors to allow photograhs of peoplein pitch dark conditions. Explain why a person (or other animal)can be seen by the camera.

5. a)Some EM waves are quite dangerous topeople. Name the three most dangerous.

.................. and .............. and ......................

b) Are these the high, or low frequencymembers of the EM family?

Worksheet 6EM Waves Questions

Student Name.............................................


15

Light Waves & ColourVisible light is just a very narrow section of the entire spectrum of EM waves.

Light includes a range of frequencies and wavelengths.We see the different frequency light waves as different colours.

Colours of the RainbowWhat we call white light is really amixture of different light waves ofdifferent frequency.

If white light (e.g. a beam of sunlight) ispassed through a glass prism, thedifferent frequencies are separated toreveal the spectrum of white light.

Are Colours Real?Each frequency of light is detectedseparately in our eye and differentsignals are sent to the brain.

It is in the brain that colours are seen.Colour really exists only as the wayyour brain interprets the informationfrom the eye regarding the differentfrequencies of light.

The light waves themselves are notcoloured. They are differentwavelengths and are vibrating atdifferent rates (different frequencies).



RedOrangeYellowGreenBlueViolet

Why Things Look ColouredSo why does one thing appear red, and another looks blue?

It is all about which frequencies of light bounce off the objects we look at.

Red Object Viewed in Blue Light

WWhhiittee lliigghhtt

AA rreedd oobbjjeeccttrreefflleeccttss oonnllyy tthheerreedd ffrreeqquueennccyy,,

ssoo bblluuee iissaabbssoorrbbeedd..

AA bblluuee ffiilltteerr lleettss tthhee bblluuee

ffrreeqquueennccyytthhrroouugghh,, bbuutt

bblloocckkss aallllootthheerrss..

NNoo lliigghhtt iissrreefflleecctteeddffrroomm tthhiissoobbjjeecctt..

TThhee bbrraaiinniinntteerrpprreettss

tthhiiss aassbbllaacckk..

Red Object Viewed in White LightWWhhiittee lliigghhttccoonnttaaiinnss aallll tthhee

ffeeqquueenncciieess..

AA rreedd oobbjjeeccttrreefflleeccttss

oonnllyy tthhee rreeddffrreeqquueennccyy..OOtthheerrss aarreeaabbssoorrbbeedd..

OOnnllyy tthhee rreeddffrreeqquueennccyy oofflliigghhtt rreeaacchheess

tthhee eeyyee..


tthhiiss aass rreedd..

Blue Object Viewed in White LightWWhhiittee lliigghhttccoonnttaaiinnss aallll tthhee


AA bblluuee oobbjjeeccttrreefflleeccttss oonnllyy

tthhee bblluueeffrreeqquueennccyy..OOtthheerrss aarreeaabbssoorrbbeedd..

OOnnllyy tthhee bblluueeffrreeqquueennccyy oofflliigghhtt rreeaacchheess

tthhee eeyyee..


tthhiiss aassbblluuee..

White Object Viewed in White LightWWhhiittee lliigghhttccoonnttaaiinnss aallll tthhee


AA wwhhiittee oobbjjeeccttrreefflleeccttss aallll tthhee

ffrreeqquueenncciieesseeqquuaallllyy..

AAllllffrreeqquueenncciieess

ooff lliigghhtt rreeaacchhtthhee eeyyee..


tthhiiss aasswwhhiittee..

You may be able to experiment with these situations using a ray-box lamp,coloured filters and coloured objects, in a darkened room.

white

blue

red

red

bblluuee

aallll rreedd

bblluuee

different frequencies spreadout to form a spectrum

of colours.

white light is a mixture of frequencies.


16

Absorption, Reflection & RefractionWhen a light wave strikes any substance, any of 3 things can happen.

Reflection of LightAll waves can reflect, or bounce off things. The reflection of sound waves causes echoes.

Reflection of radio or microwaves allows radar to work. Reflection of light allows us to see things.

AbsorptionThe energy of the wavecan be absorbed by the

substance.

Where does the energy go?It causes some of the

particles in the substance tovibrate, so it has become

heat energy.

Even substances which aretransparent, like glass orwater, absorb some light.

In perfectly clear water, lightcan only penetrate about

50m. By 100m down in theocean it is totally dark.

ReflectionThis means to bounce off.

Light always reflects atthe same angle at which ithits the reflecting surface.

More about reflectionbelow.

RefractionThis occurs when thelight penetrates into atransparent substance,such as glass or water.

The light waves changestheir speed and can

change direction.

Refraction will be covered in more detail

later in this topic.

Shiny & DullSurfaces that are very smooth (at themicroscopic level) cause parallel beamsof light to bounce off uniformly. Thisappears shiny.

Surfaces that are rougher cause lightwaves to bounce off in all directionsand scatter everywhere. Since only partof the light comes to your eye, thesurface appears non-shiny, or dull.



MirrorsMirrors are the ultimate in shiny. Theirsurface is so smooth that light reflectsoff almost perfectly.

If the mirror is flat (a plane mirror) it

forms a perfect,back-to-front

reflected image.

Curved mirrors canmagnify the image,or make it smaller.

If the curve ofthe mirror ismorecomplicated itcan formdistorted,crazy images.

Shiny,reflectingsurface

Incoming light wave

Reflectedlight wave

GGllaassssBBlloocckk

BBeeaammooff

lliigghhtt

Parallel waves in abeam of light

Parallelwavesin a

beamof light

Waves reflect uniformly.Surface appears shiny.

Light scatters in alldirections.

Surface appears dull.

Smooth surface

Rough surface(microscopically)


17

1. List (in order) the colours of thespectrum of white light.

..............., .................., ................, ..............

................., ................... and .....................

2. What colour do we see if all thefrequencies of visible light enter oureye?

3. a) Describe what happens to thevarious frequencies when white lightfalls on a green object.

b) Which frequency(-ies) reach our eye?

c) What colour do we see the object tobe?

4. Many fish are silver in colourbecause they are very shiny, and reflectall frequencies very well. Many fish arenot silver, but red when viewed in air.

In the ocean, below a depth of about 10metres, only blue & violet lightpenetrates. (All the red, orange, etc isabsorbed by the water.)a) At this depth, what colour does asilver fish appear to be?Explain.

b) What colour would a red fishappear to be?

c) Explain how being bright red (in air)might help a fish hide at 10m depth.

Worksheet 7Colour Student Name.............................................


Our brains interpret the differenta)................................ of light waves asdifferent b)........................... A mixture ofall the colours is seen as c) ..................

If white light falls on an object thatreflects the yellow frequency, butabsorbs all others, we would see it asd)............................... If we looked at thesame object under blue light (in adarkened room) it would appeare)................... because all the f).................light falling on it is being g).....................

When light strikes any substance, thereare 3 things that can happen:

it can be h)............................ by thesubstance, or i).............................. off thesurface, or it can penetrate into thesubstance and be j)..............................

When it is absorbed, the energy makesthe particles k)........................... more, soit has become l).................... energy.

If it reflects, it will bounce off at thesame m)....................... as which it hit.Flat surfaces which reflect all the wavesuniformly appear to be n)..................... Ifthe surface is rough at a microscopiclevel, the light waves bounce off ino)......................................, and arescattered. This appears p) ..................

Worksheet 8Colour & Reflection

Student Name.............................................




18

Refraction of LightRefraction can occur to all waves, but is especially important with light.

Refraction occurs when waves enter a new medium, such as light passing from air into glass or water.

Examples of Light Refraction

Experiments with RefractionYou can easily investigate refraction of light with a ray-box kit.

Just look at this spoon standing in acup of tea. It seems to be broken at thewater surface. In fact, the spoon is notbroken, and is perfectly straight.

We see the topof the spoon bylight rays thattravel throughair to our eyes.

However, lightfrom the bottomof the spoontravels throughwater, thenglass, then air to our eyes.

As light rays travel from one mediuminto the next, they change directionslightly; they are refracted.

Refraction causes the image of the bottomof the spoon to be offset from the image ofthe top of it... it looks broken.

Imagine spear-fishing from above thewater surface. You look down into theclear water, and there is dinner. Youthrow the spear with perfect accuracy...and you miss!

You are a victim of refraction!

You see the fish because of lightreflecting from it, to your eyes.However, as the light waves passedfrom water into air, they were refractedand changed direction slightly.

This caused the image of the fish to bemoved a bit. Your spear hit a falseimage.

The photograph shows a typicalexperimental investigation.

You can see that the light beams changedirection as they enter the block of clearplastic, and again (opposite direction)as they come back into air.



Things To Investigate

Rotate the plastic block so the lightbeams strike it at different angles.Do the beams always change direction?

Try different shapes of plastic blocks.(curved, triangular, etc)

Look for evidence that when the beamhits the surface:

some light reflects off it. some enters and is refracted. some is absorbed by the plastic.

LLiigghhtt rraayyss ffrroomm ffiisshh rreeffrraaccttaatt tthhee wwaatteerr ssuurrffaaccee..

IImmaaggee AAccttuuaallooff ffiisshh.. ffiisshh..

LLiigghhtt rraayyss cchhaannggee ddiirreeccttiioonn aasstthheeyy ppaassss ffrroomm wwaatteerr iinnttoo aaiirr..

TThhiiss mmaakkeess iitt llooookk aass iiff tthhee ffiisshhiiss sslliigghhttllyy ffuurrtthheerr aawwaayy..

AAIIMM LLOOWW!!

Clear plasticblock

WWoorrkk oonn aa ffllaattsshheeeett ooff wwhhiittee

ppaappeerr iinn aaddaarrkkeenneedd

rroooomm..

Light Gate allows 3 parallelbeams of light out

Ray-bbox lamp


19

Optical Lenses (Optical = to do with seeing things)We use many optical devices to help us see things better.

Spectacles and contact lenses correct peoples vision. Microscopes magnify tinyobjects, while telescopes make distant objects look closer. Cameras and projectors

focus images onto film or onto a screen for viewing.All of these rely on curved lenses which refract light in special ways.

Convex LensesIf you look through a convex lens atclose-up things (e.g. the writing on apage) you will quickly find out that aconvex lens is a magnifying glass.

Using a ray-box kit, you can see what aconvex lens does to parallel beams oflight, by refraction.

Concave Lenses(They go in, in the middle, like a cave)Using a ray-box kit, you can see that aconcave lens does NOT refract light to afocus, but spreads the beams apart.

Only a convex lens can focus an imageonto a screen or film, so they are themain lenses in cameras, projectors, etc.

FFooccuuss,,oorr FFooccaall PPooiinntt

PPaarraalllleell bbeeaammssooff lliigghhtt

Convex Lenssseeeenn eeddggee oonn

Concave Lens

Focusing an ImageWith a Convex Lens

You might try this activity.

Try again with a concave lens... it will not work.

Images can only be focused on ascreen by convex lenses.



LLiigghhtt rraayyss ffrroomm aaccaannddllee ppllaacceedd sseevveerraall

mmeettrreess aawwaayy

In a darkened room, hold a convex lens in front of apaper screen. Move lens or paper back-aand-fforth to

focus the image of a distant, lit candle onto the screen.

Upside-down image

of candleforms on

paper screen

How the Eye WorksOur eyes are optical devices. Inside the eye a convex lens focuses an image on

light sensitive cells in the retina. From there, nerve messages are sent to the brain.

Optic NerveCarries nerve signals from

Retina to brain.

Retinais sensitive to

light, and sendsoff nerve

messages.

The eyeball is filled with a clearjelly-lliquid. This keeps the eyes

shape, and lets light through.

Lens is transparent & flexible. It refractslight to focus an image on the retina.

The shape of the lens changes according tothe distance of the object being viewed.

Iris is the colour of the eye.It is a ring of muscle which canopen or close the hole in the

middle... the Pupil. This controls the amount of light

entering the eye.

Light Rays


20


Refraction occurs when a wave enters anew a)............................., such as whenlight goes from air into b)........................

Refraction can cause waves toc)............................................... slightly.This can cause the image of things to bed)......................... slightly, when viewedthrough glass or e)........................

A f)......................... lens is made ofcurved glass which is thicker in themiddle. It refracts rays of light so thatthey all meet at a g)....................... point.This type of lens can h).............................an image onto a screen, as in aprojector.

This type of lens can also act as a i) ....................................... glass tomake things look bigger. Thats whythey are used in j)........................... tomake small things appear larger, and ink)............................ to make distantobjects look closer.

A l)............................. lens is curved theopposite way so it is m)...........................in the middle. This type will notn).................. light rays and cannotproject an image.

The eye is an o)............................ devicecontaining a p)......................... lens. Thelens focuses light onto light-sensitivecells in the q)............................ Thissends r).................... messages to thes)............................, where we actuallysee things.

Worksheet 9Refraction & Lenses Student Name.............................................

1. The diagram shows a flat mirror. P,Q&R are 3 light rays striking the mirror.Use a ruler to sketch the path of eachreflected ray.

2. This diagram shows a beam of light striking a block of glass. As it hits the glass some of the beam reflects and some refracts. Sketch and label clearly the 2 parts of the beam.

3. In the situation shown in Q2, whatelse may have happened to some of thelight in the beam?

4. Complete these diagrams to show thepath of the light rays that pass throughthese 2 lenses.

Also name the type of lens in each case.

....................

....................... lens

Worksheet 10Reflection & Refraction Student Name.............................................



P

Q

R

glass




21

Topic Test Wave EnergyAnswer all questionsin the spaces provided.

1. (5 marks) True of False? T or Fa) Light and sound waves can

both travel through a vacuum. ......b) The water only moves up &

down as a water wave passes. ......c) Amplitude is measured from

trough up to crest. ......d) The highest frequency EM

waves are radio waves. ......e) A red object viewed in red

light would appear red. ......

2. (4 marks)Fill in the blank spaces.

The wavelength of a wave is the distancea)...................................................................The frequency is a measure of howmany b).......................................... per sec.The unit of frequency is the c)...................For any type of wave, if the wavelengthgets shorter, the frequency getsd)...........................

3. (3 marks)Small water waves in a lake have awavelength of 1.5m. Their frequency is0.5Hz. What is their speed?Shown full working, and units for answer.

4. (2 marks)Mark clearly on this wave diagram themeasurements of amplitude and wavelength.

5. (5 marks)Match each description to an item fromthe list. To answer, write the letter (A,B,C,etc) of the list item beside thedescription.

Description matches with List Item

a) The substance that a wavetravels through. .............

b) Shortest wavelength EMwave. .............

c) What lenses do to light rays. .............

d) EM wave used to cook. .............

e) Lens that can focus light. .............

List Items Not all will be used. Some may be used more than once.

A. refraction D. gamma raysB. medium E. convexC. concave F. microwave

6. (3 marks)This diagram shows a ray of light strikinga flat mirror at a 45o angle. There are 2lenses nearby, exactly as shown.

Use a ruler to construct the path taken bythe light ray.

Student Name............................................. Score = /22

22Years 9-10 Topic 12 Wave Energycopyright 2008 keep it simple sciencewww.keepitsimplescience.com.au

Answer SectionWorksheet 1a) energy b) mediumc) oscillate / move up & downd) go anywhere e) soundf) vacuum g) mediumh) light i) glass or waterj) electromagnetic k) 300,000 km/hrl) crests m) troughsn) up & down o) amplitudep) volume q) brightness

Worksheet 21.

(c) wave R (smallest amplitude)2. The cork moves up and down only.3. Light waves can travel through avacuum, but sound waves cannot. (No airon the Moon... vacuum.)4. By radio, which is an EM wave and cantravel through a vacuum.

Worksheet 31. v = x f = 0.5 x 660 = 330 m/s

2. v = x f = 0.1 x 3,300 = 330 m/s

3. v = x f = 50 x 0.05 = 2.5 m/s

4. v = x f = 0.4 x 3 = 1.2 m/s

5. v = x fso = V/f = 330/1,000 = 0.33 m

6. v = x fso = V/f = 1,500/1,000 = 1.5 m

Worksheet 41. a) 50,000 = 5x104 Hzb) 6 km = 6,000 m = 6x103 mc) v = x f = 6x103 x 5x104

= 3x108 m/s

2. v = x f = 0.8 x 3.75x108= 3x108 m/s

3. V = x f, so = V / f = 3x108 / 2.5x109

= 0.12 m (= 12 cm)

4. V = x f, so f = V / = 3x108 / 1x10-5

= 3x1013 Hz= 30,000,000,000,000 Hz

5. V = x f, so = V / f = 3x108 / 6x1014

= 5x10-7 m

6. V = x f, so f = V / = 3x108 / 5x10-9

= 6x1016 Hz

7. V = x f, so f = V / = 3x108 / 3x10-11

= 1x1019 Hz

8. V = x f, so = V / f = 3x108 / 5x1021

= 6x10-14 m

Worksheet 5a) electromagnetic b) 300,000 km/sc) medium d) loweste) radio f) radio & TVg) shorter h) higheri) cooking or GPS or radarj) Infra-red k) skinl) light m) seen) Ultra-violet o) ozonep) X-rays q) penetrate throughr) Gamma s) radio-activet) shortest u) highest



P

Q

Crest

Trough

(a)

(b)


Worksheet 61. radio & microwaves2. They can all travel through the vacuumof space, carrying information about theUniverse.3. Speed of light = 3x108m/s =300,000km/s4. Our body heat gives off infra-red waveswhich are detected by the camera.5. a) UV & X-ray & gamma raysb) high frequency

Worksheet 71. radio, microwaves, infra-red, light,

ultra-violet, X-ray, gamma2. white3. a) The green light frequency isreflected, but all others are absorbed.b) Green frequency only.c) Green.4. a) Silver fish would appear to beblue/violet because those are the onlyfrequencies of light in the water. They willreflect off the fish to our eyes.b) Black. The fish appears red at the surfacebecause only red frequency reflects off it.Blue & violet frequencies would beabsorbed. c) Looking black, it could hide in anyshadow (under weed or a rock) and notbe seen.

Worksheet 8a) frequencies b) coloursc) white d) yellowe) black f) yellowg) absorbed. h) absorbedi) reflected j) refractedk) vibrate l) heatm) angle n) shinyo) all directions p) dull

Worksheet 9a) medium b) glass / waterc) change directiond) offset / shifted e) waterf) convex g) focalh) project i) magnifyingj) microscopes k) telescopesl) concave m) thinnern) focus o) opticalp) convex q) retinar) nerve s) brain

Worksheet 101.

2.

3. Some was absorbed.4.

Concave Convex



P

Q

R

glass


Topic Test1. a) F b) T c) F d) F e) T

2.a) from crest to crestb) waves go by per sec.or, vibrations occur per sec.c) hertz (Hz)d) higher

3. V = x f = 1.5 x 0.5 = 0.75 m/s

4. wavelengthampl

5. a) B b) D c) Ad) F e) E

6.keep it simple science


wave energy, kiss

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