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USE THE ITEMS PROVIDED TO LEARN ABOUT LIgHT AND cOLOUR.

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SPARK!� DISCOVERY BOXES � �are to be used with adult supervision AT ALL TIMES.Light and Colour

WHAT’S IN THE BOX?

Wind-up LED torch

Spray bottle (please dry after use)

Set of lenses of different types

Blank cD

Spectroscope

7

2 Light and Colour

What is light?

Light is one type of radiation produced by stars (including our sun), by some creatures and reactions, and by lamps and flames. Similar types of radiation include radio waves, microwaves, infrared, ultraviolet and X-rays.

We can think of radiation as invisible waves travelling through space. We only see things that produce or reflect radiation of certain wavelengths.

From longest to shortest wavelength, most people see red, orange, yellow, green, blue, indigo and violet light. If light of all these colours combines, it appears white.

•USEtheCDtosplitwhitelight.Observethedifferencesbetweensunlight,fluorescentlight,incandescentlight(suchasfromahalogenlamp,atorchwithglobethatcontainsafilament,oracandle–underadultsupervision)andLEDlightfromthetorchinthekit.Ifyouhaveheatlampsinyourbathroom,observetheirlightaswell–andfeeltheirheat,whichisinfraredradiation.Drawsomeofthecolourpatternsyousee,andtakephotosoftheCDlyingonasheetofpaperbesidethenameofthesourcewhoselightitissplitting.

•Ifyouhadtroubleseeingallthecoloursofthespectrum,DIScUSSthiswithanadult.Findsomeonlinetestsforcolour-blindnessandworkthroughthemtogether.Ifyoudodiscoveryouhaveacolourvisionproblem,

encouragefamilymemberstotakethetest,becausethisconditionisgenetic.Whileitisabitinconvenient,ithasnoothereffectsoneyesight.

•Ifyouhaveagardenhose,standwithyourbacktotheSunandcREATEafinespray.Ifnot,fillthespraybottlewithwaterfortheexperiment.Moveyourbodyandthesprayuntilyouseearainbow.Whatcolourscanyousee?(Manypeoplefindithardtodistinguishbluefromindigoinarainbow.)Drawapictureofyourself,theSunandyourownlittlerainbow.

•FINDsomephotosofrainbows.Searchforonewithafaintersecondaryrainbowoutsidethemainone.Whatdoyounoticewhenyoucomparethecoloursintheprimaryandsecondaryrainbows?Findadiagramthatexplainshowprimaryandsecondaryrainbowsform.

•SHINEthetorchatsomethingblue.Describe,inwordsorapicture,whathappenstothecoloursinthewhitelightwhenithitstheobject.Mostobjectsscattersomeofthewhitelightthathitsthemaswellasabsorbingsomewavelengthsandreflectingothers–doyouthinkthisishappeningwiththeobjectyouchose?

•SHINEthetorchatapieceofcolouredfabric.Pouralittlewateronthefabricandobserveanychangeinitsappearance.Writeabriefexplanationintermsofabsorption,reflectionandscatteringoflight.

Light and Colour 3

When the Sun is low in the sky near sunrise or sunset, light reaches us

through a longer column of air than at noon. So it encounters more

molecules and particles in the air, which scatter more blue light.

The light that reaches us therefore appears orange or red, and the

colour is stronger if there is more dust in the air.

Why is the sky blue?

•Halffillaclearglassorplasticcontainerwithwater.Shinethetorchthroughthewaterfromonesidewhileobservingfromabove.Nowaddafewdropsofmilktothewater,stirandrepeatyourobservation.AddalittlemoremilkandOBSERVEanychanges.

•Shiningthetorchlightthroughthewaterinthesamewayasbefore,OBSERVEfromapositionoppositethetorch.Whydoyouthinkthelightherelooksyelloworred?Rememberthatwhitelightisacombinationoflightofdifferentcolours,andthatpartofthewhitetorchlighthasbeenscatteredbythemilk.Addsomemoremilkandnoteanychanges.

•DRAWadiagramtoshowwhatyouobserve,bothfromaboveandfromoppositethetorch.

Milkcontainssmallparticlesthatscatterlight.Gasmoleculesandsmall

particlesofdustintheairalsoscatterlight.Inbothcases,theparticlesscattermorebluelightthanred,makingthemilky

solution,andthesky,blue.

What do mirrors do to light?

•LOOkatyourfaceinaverticalmirror.Howdoesyourreflectioncomparewithyourface?Shutyourrighteyeandwatchwhicheyeyourmirrorimageseemstoshut.Yourbrainthinksyouarelookingatapersonwho’sfacingyouandshuttingtheirlefteye.

•STANDinfrontofaverticalmirrorandpointonefingerupwards.Movethefingerinahorizontalcircle,turningyourhandclockwise.Observeitsmotioninthemirror–isitclockwiseoranticlockwise?

•Whatdoyoupredictyouwillseeifyoumoveyourfingerclockwiseinaverticalcircle,pointingatthemirror?NowdothisandOBSERVEwhathappens.

•UNDERSTANDreflectioninamirror?Askanotherpersontostandfacingyouandwatchyourepeattheseactions.Thenaskthemtorepeattheactionswhileyouwatch.Discusshowyouseeeachother’shandmoving.

•STANDfacinganarrowverticalmirror.Moveonehandslowlytotheside,asfarasyoucanreach.Keepmovingyourheadsoyoucanalwaysseethehand.Drawadiagramshowinglightfromyourhandbeingreflectedinthemirrorandreachingyoureyes.

•LOOkatyourfaceinbothsidesofashinyspoon.Writedownyourobservations.Drawyourcartoonface,perhapswithabignose,widemouthorsmallchin(orallthree).

4 Light and Colour

Which photo shows a face reflected by the concave front of a spoon, and which

by its convex back?

Light is bent by the two lenses inside a telescope and by the lens in the eye.

An object standing partly in water and partly in air appears to be broken at the surface

of the water because light is bent (refracted) when it travels from one transparent medium

(such as air, water, glass or plastic) into another.

Lenses are designed to bend light in interesting and useful ways as it travels from air into

glass or plastic and back into air.

What do lenses do to light?

•PLAcEathinobjectsuchasapenorchopstickinaglassofwater,withpartofitabovethesurfaceofthewater,andobserveitfromtheside.

•PLAcEacoinonthebottomofanopaquecup.Moveitawayfromyousothatthecoinisjustoutofsight.Pourwaterintothecup.Toexplainwhatyouobserve,drawdiagramsthatshowthepathoflightfromthecointoyoureyebeforeandafteryouaddedthewater.

•PLAcE thelensesonaflatsurfaceinadarkenedroom.Shinethetorchateachlensandobservehowitbendsthelight.Sketchthepathoflightforeachlens.

•PLAcEtwolensessothatlightfromthetorchtravelsthroughoneandthenthroughtheother.Experimentwithdifferentcombinationsoflenses,atdifferentdistancesapart,anddrawthepathofthelightineachcase.

•LOOkatthistextthroughthelenses.Drawtheshapeofthelensthatmagnifiesthetext.Thisisthesameshapeasthelensthatfocuseslightonthebackofyoureye.

•USE themagnifyinglenstolookatacomputerscreen.Whatcolourpixelsinthescreencombinetomakewhite?

Light and Colour 5

6 Light and Colour

Can you watch colours mixing?•POURwaterintoatallglassuntilitisabouttwo-thirdsfull.Placeonedropeachofred,blueandyellowfoodcolouringonthesurfaceofthewater,spacedwellapart.Placeasheetofpaperbehindtheglassandwatchthecoloursmix.Doyouseethecoloursyouexpected?

•POURwatertoabout2cmdepthintoalargewhitecontainerandletitstandfortenminutessothewaterisstill.Addonedropofeachcolour,spacedwellapart,andtimehowlongtheytaketomix.Takephotostoshowthestagesofmixing.

Can you measure light?Scientists often perform simple qualitative experiments when they explore a new field. This is what you did with the CD, exploring and observing light without measuring anything.

To understand more about the world, scientists then devise quantitative experiments, ones that involve measurement. They have invented all sorts of instruments to help in these measurements.

The spectroscope is an instrument for separating the colours in light and measuring their wavelengths. Using spectroscopes, scientists can analyse the chemical composition of distant stars and gain a deep understanding of the substances around us.

•USEthespectroscopetoobservesomeofthelightsourcesthatyouexploredwiththeCD.Recordthewavelengthofeachcolourasmeasuredbythespectroscope.

Aspectroscopeusescloselyspacedlinestodiffractlight,justasthetinygroovesonaCDdo.Lightisdiffractedwhenitencountersaslitaboutthesamesizeasitswavelength.

•FIND somephotosofdiffractionofwaterwaves.Lightwaveshaveamuchsmallerwavelengththanwaterwaves,buttheycurveinasimilarwaywhentheymeetasmallslit.

In this photo, waves moving from left to right are diffracted by the gap in the barrier, just as light waves are diffracted by a tiny slit.

Grating spectrometer schematic

Light and Colour 7

Why are bubbles colourful?

A bubble is a very thin film of water and detergent. When light hits it, some is reflected by the outside of the film and some is reflected (a short time later) by the inside of the film.

When these two slightly different reflected light waves overlap, some wavelengths (colours) become stronger and others become weaker or disappear.

This effect is called interference. The particular colours you see depend on the time lag and thus on the thickness of the film.

•ADD1tablespoonofthickkitchendetergentto1cupofwaterinasmallbowl.Dipthetopendofaplastictumblerinthesolution,holditsothefilmacrosstheendisvertical,andobservetheeffectoflight(fromtheSunorthetorch)onthethinfilmthatforms.Movethetumbleruntilyouseebandsofcolournearthetopofthefilm.Whatcolourscanyousee?

•OBSERVEthefilm.Whatcolourscanyouseefromtoptobottom?Howdoesthischangeovertime?Whydoyouthinkthepatternofcolourchanges?Hint:considertheeffectofgravityonthefilm.

•STANDbesideawindowonasunnyday,ornearabrightlight.Dipastrawinthemixtureandblowafewbubblesinthebowl.Gentlypierceonebubblewiththestrawandblowitupfurther.Canyouseebandsofcolour?Canyouseebrightspotsofdifferentcolours?Watchthemandnotehow

theychangeovertime.Deviseyourownexperimentswiththebubblemixtureandwriteinstructionsthatsomeoneelsecouldfollow.

•FINDphotosofinsectsandbirdswithiridescentparts.Theirbrightcoloursareduetointerference.Youwillalsoseethiseffectinsidesomeseashellsandinoilspillsthathavespreadouttoformathinfilmonthesurfaceofawetroad.

•READthestoryofThomasYoung,whoaskedinterestingquestionsaboutlight,colourandhowoureyeswork.Hecarriedoutimportantexperimentsandwasthefirstpersontoexplaininterference–acenturyaftertheeffectwasfirstdescribedbyscientists.Hisworkshowedthatwavetheoryisverygoodatexplainingmanyaspectsoflight.Today,itisstillveryusefultothinkoflightasawave,eventhoughpicturingitasastreamofparticles(photons)ismoreaccuratewhenexplainingsomeeffects.

For assistance, further information or general feedback, please send an email to spark@childrensdiscovery.org.au

For assistance, further information or general feedback, please send an email to spark@childrensdiscovery.org.au