Presentation on theme: "Light Reflection and Refraction"— Presentation transcript:
1 Light Reflection and Refraction Topics: LightSubtopics: sources and transmission of light, speed of light, shadows; colour and the visible spectrum; dispersion and white lightTopics: Reflection of Light; Refraction of LightSubtopics: reflection of light at plane surfaces; image in a plane mirror; refraction; refraction by lenses; application of reflection and refraction
2 Lessons Lesson – 1 80 minutes OP33 Light Energy OP34 Light TransmissionOP35Luminous &Non-LuminousLesson – 2OP38ReflectionOP39RefractionLesson – 340 minutesOP36Light SpectrumOP37Produce a SpectrumThis is a hidden slide and will not appear in any slide show. It does however link to the different lessons as I have split them up.
3 Learning OutcomesOP33understand that light is a form of energy and that it can be converted to other formsOP34show that light travels in straight lines and explain how shadows are formedOP35understand that luminous objects are a source of light while non-luminous objects are seen as a result of light reflected from themTopics: LightSubtopics: Sources and transmission of light, speed of light, shadowsLesson Time: 40 minutesThese learning outcomes are what the student will be able to accomplish after the lesson.The underlined learning outcomes indicate those for higher level students only.Learning outcomes coloured blue indicate practical work.PRESENTATION NOTES:Click on the learning outcome to view the presentation for that outcomeThis slide is hidden and will not appear in a screen presentation.It will appear in the notes only if you choose to print hidden slidesClick on the button ‘Lesson Menu’ to go the lesson choice slideLessons
4 Learning OutcomesOP36Recall that white light is made up of different colours which can be separated by dispersionOP37Produce a spectrum of white light using appropriate apparatus, and list the colours of the spectrum.Lesson Time: 40 minutesTopics: LightSubtopics: colour and the visible spectrum; dispersion and white lightThese learning outcomes are what the student will be able to accomplish after the lesson.The underlined learning outcomes indicate those for higher level students only.Learning outcomes coloured blue indicate practical work.PRESENTATION NOTES:Click on the learning outcome to view the presentation for that outcomeThis slide is hidden and will not appear in a screen presentation.It will appear in the notes only if you choose to print hidden slidesClick on the button ‘Lesson Menu’ to go the lesson choice slideLessons
5 Learning OutcomesOP38investigate the reflection of light by plane mirrors, and illustrate this using ray diagrams; demonstrate and explain the operation of a simple periscopeOP39show the refraction of light as it passes from: air to glass, air to water, glass to air, water to air; show refraction of light through a lens; demonstrate the operation of a magnifying glassLesson Time: 40 minutesThese learning outcomes are what the student will be able to accomplish after the lesson.The underlined learning outcomes indicate those for higher level students only.Learning outcomes coloured blue indicate practical work.PRESENTATION NOTES:Click on the learning outcome to view the presentation for that outcomeThis slide is hidden and will not appear in a screen presentation.It will appear in the notes only if you choose to print hidden slidesClick on the button ‘Lesson Menu’ to go the lesson choice slideLessons
6 Light is a Form of Energy ‘the’ source of energy for plantsIndirect source of energy for animalsSlide Aim:To show light as a source of energyLight can be converted from one form of energy to anotherProbing Questions?With respect to flowers, what effect does the sun have?What is the difference between something that is direct/indirect? Give an example?Explanation:Plants capture sunlight inside their leaves and use it to make sugar and grow (Photosynthesis).Sugar is a form of chemical energy that other animals can feed on.Photosynthesis: Radiant energy chemical energy (sugar)Basic reaction: Carbon dioxide + water + light energy = oxygen + glucose (chemical energy)Light Energy
7 Conversion of Light Energy Light kinetic energyCrookes RadiometerLight Electrical EnergySlide Aims:To show that light can be transformed from one energy type to another.Probing Questions?Can anyone give examples of objects that require light to work?Questions: Latest James Bond movie….what was ‘the baddies’ weapon of choice to destroy armies?Answer: Satellite that focussed suns energyQuestion: What is the energy source for the Big Brother house every year?Answer: Solar Panels on roof of house.Give details of Crooks Radiometer to explain how light energy is converted to energy of motionCrookes RadiometerThe radiometer consists of a glass bulb, from which much of the air has been removed to form a partial vacuum.Inside the bulb, on a low friction spindle, are several (usually four) lightweight metal vanes.Each vane is polished on one side, and blackened on the other.In sunlight, or exposed to a source of infrared radiation (even the heat of a hand nearby can be enough), the vanes turn with no apparent motive power.Light to electrical EnergyExamples: Solar Powered Calculator, lighthouse, spacestation, garden lampsLight energy hits solar module module connected to a charge controller charge controller leads to battery
8 Luminous/Non-Luminous Bodies An object is seen when light from it reaches eyesLuminous objects give out lightNon-luminous objects don’t give out lightHow can we see non-luminous objects?Sources of light – luminous objectsSun, stars, candle, lamp, fire and other chemical reactionsSlide Aims:To introduce the concept of luminous and non-luminous objectsTo discuss concept that we can see things that don’t give out light due to reflectionTeaching Methodology:Teaching again is done by enquiry. A question is put to the class and through discussion an answer is achieved. Teacher should act as facilitator only in discussion and to guide the class in the right direction.Probing Questions:Question: If we only see an object when light from it reaches our eyes, how can we see non-luminous objects?Answer: if successful, the class will mention reflection and this process can be expanded upon.Question: List luminous objects?Answer: Given in slideQuestion: What chemical reactions might produce light?Answer: fire burning, explosionsQuestion: What other form of energy is frequently associated with a light source?Answer: heat
9 Seeing Non-Luminous Objects Slide Aims:To demonstrate how we see non-luminous objectsConclusion:Through demonstration above and class questioning the conclusion should be drawn that…We see non-luminous objects by reflection from luminous objects.Examples of this effect:Cat’s eyes – reflect light from carsReflective vests/armbands as well as bright clothes reflect light to motorists…dark clothes do not reflect lightMoon, sun, stars and planets create light – even in a dark room eyes become accustomed to light that leaks into roomNon-luminousobject
10 Grand Central Station, New York Transmission of LightLight travels in straight linesCan you give examples?Grand Central Station, New YorkSlide Aim:To show that light travels in straight linesProbing Questions:How does light travel? Try to tease out the answer by the way of giving them one example?Possible examples:Stars in star trek when the ship goes to warp speed!lights at disco through dry icelights of car in foglaser beam at concertssunlight through clouds/treesDiscuss other examples and what conclusion may come from it. With success they will recognise that light travels in straight lines.
11 To Show That Light Travels in Straight Lines cardboardlightbulbSlide Aim:Give diagram of experiment to show light travels in straight lines.Allow students to understand how to perform experiment themselvesMethod:Set up the apparatus shown in the diagramPosition the cardboards so that the light can be seen through the holesCarefully pull the thread tight. You will notice that all the holes are in the same staight lineIf you now move one of the cardboards out of position, the light will no longer be seen.Conclusion:Light travels in straight linesthread/stringMandatory Practical
12 To Show the Formation of Shadows White Sheet/CardboardObjectSlide Aim:Give diagram of experiment to show the formation of shadowsAllow students to understand how to perform experiment themselvesMethod:For this experiment, a point source of light works best. Suitable sources include a ray box with the slit removed, a torch, or sunlight coming in through the window.Place a sheet of white paper or cardboard where it is well lit by the light sourceHold any object (hand, key, pencil) near the paper and see the shadow that is formed.Result:The formation of a shadow which is the same shape as the outline of the objectConclusion:Light travels in straight lines past the edges of the object but a shadow is formed where the object blocks the light.This also shows that light travels in straight lines.TorchMandatory Practical
13 Light Speed 300 million metres per second (3x108 m/s) Sun Earth (150million miles)takes ~8 minutesLight year – distance light travels in 1 yearHow many seconds in a year?Answer: 9,460,000,000,000kmSlide Aim:To introduce the speed of lightQuestion:Try to get students to work out how many seconds are in a yearFrom this figure calculate the distance travelled in a light yearLight year = 60x60x24x364 x (3x108)= km (9.46x1012km)
14 Reflection Practically all surfaces reflect light Shiny smooth surfaces have regular reflectionMatt (dull) surfaces have scattered reflectionSlide AimsTo introduce concept of reflectionKnow why smooth surfaces appear more shiny (more light reflecting in a straight line towards the eye)Know why rough surfaces appear duller (light rays scattered – may not all direct towards eye)PointsLight does not bend it reflects – in effect bounces off a surfaceWhat happens when you look in a mirror? What are you looking at?
15 Uses of Reflection What are some uses of reflection? Mirror, periscope (used in submarines)mirror at 45o angleSlide Aims:To get student thinking about uses of reflection.Demonstrate how a periscope worksExamples:Cats eyesMirrorPeriscopeReflective jacketsPeriscope
16 To show reflection of light by a plane mirror and to demonstrate the operation of a periscope light boxlight boxbulb inside boxsheetpencil markmirrorSlide Aims:Give diagram of experiment to show the reflection of light by a plane mirror and to demonstrate the operation of a periscopeAllow students to understand how to perform experiment themselvesLots of animation: Run the slide to completion before asking students to complete exerciseExperiment Procedure:Arrange the apparatus as show in the diagram so that a ray of light strikes the mirror.Rotate the mirror. What happens the ray of light that is reflected from the mirror?Set the mirror in one position, and mark its position on the paper.Using pencil dots, mark the position of the two rays of lightMark the position of the back of the mirror, label the rays of light and put arrows on them to show their direction.Where the rays meet at the mirror, draw a line that is perpendicular to the mirrorMeasure the angles that the rays make with the perpendicular lineRepeat for other rays at different anglesIllustrate the principle of the periscope by using two mirrors and arranging them as show in the diagram on the previous slidemirrorFrom the topMandatory Practical
17 Refraction is the bending of light from one medium to another Refraction of LightWhy do objects appear contorted under water?Why does a swimming pool look shallower than it really is?Light travels in straight lines through air, glass, water etc.BUTWhen it passes from one to the other it changes direction.Slide Aims:Introduce refractionDemonstrate the effects of refraction through examplesExplanation of Questions:Because a ray of light changes direction at a water surface, your eye thinks that the light has come from a different point. This is why the depth of water appears to be less than it really is.Refraction is the bending of light from one medium to another
18 Refraction Demonstration light boxsheetrefraction fromair to glassoccurs hereglass blockSlide Aim:To demonstrate how refraction occurs in a glass blockExperiment procedure:Arrange the apparatus as shown in the diagram so that a ray of light strikes the glass block at an angle, enters it and comes out the far side.On the paper; draw the outline of the glass block, and then draw the positions of the light rays which enter and leave the block.Remove the glass block, and draw a line showing the direction of the light as it went through the block. Put arrows on all rays of light to indicate their direction.Note: When a ray of light goes into the block, the angle in the block is smaller than the angle (i) at which it enters. Conversely, when the ray of light comes out of the block, the angle outside the block is larger than the angle inside it. The same thing happens with water; when light enters a water surface, it is bent inwards; on emerging from the water; it is bent outwards.Plan view of experiment to demonstrate refraction
19 Lenses Simple optical devices Curved surfaces use refraction to focus Convex/converging lens (fat in the middle)Concave/diverging lens (thin in the middle)Example: magnifying glassSlide Aims:Demonstrate the effects of lenses on lightDistinguish between concave and convex lensesGive sample uses for each type of lenseExample: lenses of short sighted people
21 Red, Orange, Yellow, Green, Blue, Indigo and Violet Spectrum of LightWhere do the colours of the rainbow come from?Are they always the same colours?YES!The name given to the splitting up of white light into its separate colours is dispersionColour SpectrumRed, Orange, Yellow, Green, Blue, Indigo and VioletSlide Aims:To introduce/recall the spectrum of colours that make up white light
22 Producing a Colour Spectrum light boxColour SpectrumRed, Orange, Yellow, Green, Blue, Indigo, Violetbulb inside boxprismSlide Aims:To explain how to produce the colour of the spectrum from white lightOrigins:One day a ray of sunlight entered Newton’s darkened laboratory through a hole in the shutters and fell on a prism (a triangular shaped piece of glass) on his bench. A band of colours was produced on the far side of the room. Newton then discovered that if he recombined all the different colours using a second prism, he got back white.Procedure:Arrange the apparatus as show in the diagram so that a ray of light passes through the prismRotate the prism to produce as good a spectrum as possible.Draw a diagram and label the different partspaper or cardscreen
23 Homework Suggestions Why is the sky blue? Why are sunsets orange? Why is sunburn more likely to occur if you are up a high mountain or at the beach?How do photosensitive sunglasses work?Why are soap bubbles coloured in white light?Why are compact discs coloured?Why are sunglasses of particular benefit to fishermen?How would a rainbow appear to passengers in an aeroplane when there is rain in the air above and below them?Why do materials purchased in a shop appear a different colour in daylight?How does the eye see colour?What causes after images and what colour are they?If black is a good absorber of heat, why do Bedouins wear black robes in the hot desert?Why is the filament of an electric light bulb coiled?Why is a firefly a more efficient light producer than a filament lamp?Note: This is a hidden slide that will not appear in the main presentation.Slide Aims:For teachers guidance, it is a useful exercise for each student to think of any of the above questions and attempt to answer them. Maybe a class discussion in the next class would determine the answers to many of them.Recommendation: Split the class into groups and spread the questions between the groups. Class discussion on these in the next class.Why are soap bubbles coloured in white light?The light waves reflected from the front and back surfaces of the bubble interfere, resulting in different colours being in phase at different angles.Why are compact discs coloured?The disc acts as a diffraction grating. When the disc is illuminated with white light the reflected light from each ‘groove’ acts as a new source and, due to interference, coloured lines appear.Why are sunglasses of particular benefit to fishermen?The reflected light from the surface of water is partially polarised horizontally, i.e. parallel to the surface, and the glare from this is blocked by the vertical polarisation of the glasses. The refracted light which passes into the water must be polarised vertically so when this light is reflected by a fish it can all pass through the glasses. The fish can be clearly seen but the glare is blocked.How would a rainbow appear to passengers in an aeroplane when there is rain in the air above and below them?It should appear as a complete circle as the rays reaching the passengers from all directions which are at an angle of 42° with the line from the sun to the aircraft will display the rainbow.Is a rainbow polarised?Yes. As the light is reflected within the rain drop it will undergo partial polarisation.Why do materials purchased in a shop appear a different colour in daylight?White light contains colours of all wavelengths from red to violet but they are not present in equal intensities. In sunlight the greatest intensities are in the green and blue portions of the spectrum while an incandescent bulb has greater intensity in the yellow to red portion of the spectrum. The colour observed is due to the light reflected from the material. This in turn depends on the light incident on the material. The difference in colour of the material is therefore due to the difference in intensities of the various colours in the artificial light compared with sunlight.Why is the sky blue?The gas molecules in the atmosphere scatter the light. The amount of scattering depends on the wavelength of the light, the shorter wavelengths (the blue end of the spectrum) being scattered preferentially. This was first explained by the Carlow-born scientist, John Tyndall.What is scattering?The oscillating magnetic and electric fields which constitute light moving across a molecule cause a sympathetic vibration of the same frequency in the molecule. In other words, the molecule absorbs light energy of that particular frequency. The oscillating molecule then re-emits the energy as radiation of the same frequency but in all directions. So the light which had been travelling in one direction has now been ‘scattered’ in all directions, including towards the earth. Since it is mainly the shorter wavelengths, i.e. the blue light, which are scattered the sky appears blue in all directions except when we look directly towards the sun. Scattering may also be caused by small particles, e.g. dust, in the atmosphere.Why are sunsets orange?At sunset the light rays from the sun are travelling through greater lengths of atmosphere so the amount of scattering of the blue light increases and the percentage of the reddish light reaching our eyes increases giving the setting sun an orange-red colour. Dust in the atmosphere also contributes to the scattering of the sun’s light. This accounts for the variety of shades of red in the evening sky. A particularly striking example of this occurred following the eruption of Mount Krakatoa in The dust from the eruption (some 20 km3 of rock fragments were hurled up to 80 km into the atmosphere) resulted in spectacularly coloured sunsets around the world throughout the following year.How does the eye see colour?There are three different types of cone cells in the retina of the eye which allow colour vision. Each of these cells contains a different pigment labelled blue, green and red, as in the primary colours. Each cone absorbs over a range of wavelengths so there is considerable overlap and one wavelength of light may be absorbed by one, two or three different types of cone. About 8% of the population are colour-blind, that is they are unable to distinguish red – green colours. Most colour-blind people have three different cone pigments but the ranges of wavelengths absorbed by the cones do not overlap sufficiently to enable them to respond to different hues. A minority of colour-blindness is due to the presence of only two types of pigment in the cone cells.What causes after images and what colour are they?If you stare at a bright colour for fifteen seconds and then look at a white wall you will see the after image in the complementary colour. The light coming from the colour tires that part of the retina of the eye sensitive to the colour so, on looking at the white wall, the part of the retina which is not tired dominates and the complementary colour is seen.If black is a good absorber of heat, why do Bedouins wear black robes in the hot desert?The hotter black robe warms the air inside the robe by about six degrees Celsius more than a white robe would. This hot air rises and passes out through the fabric, with cooler air coming in at the bottom to take its place. This creates a continuous draught, due to convection, passing over the body. This cools the body, making a black robe more comfortable to wear than a white one.Why is the filament of an electric light bulb coiled?The filament is coiled to reduce heat loss. The higher the temperature the whiter the light. If the filament is uncoiled then it will only glow dimly.Why is a firefly a more efficient light producer than a filament lamp?The firefly produces ‘cold’ light so no energy is wasted in the production of heat, as occurs in the filament lamp. (This also explains why fluorescent lamps are more efficient than filament lamps.) The firefly is 100% efficient; one photon is emitted for each molecule oxidised.Why is sunburn more likely to occur if you are up a high mountain or at the beach?On a high mountain the path travelled by the ultraviolet radiation through the atmosphere is reduced, so the amount absorbed by the atmosphere is also reduced. This gives a greater concentration of ultraviolet radiation than at ground level and therefore more sunburn. On the beach the ultraviolet radiation is reflected by the sand, so this again gives a greater concentration and more sunburn.How do photosensitive sunglasses work?The glass contains small crystals of a chemical, e.g. silver bromide. When the light falls on the glass the silver ions are converted to silver atoms which then darken the glass. In the dark the silver atoms will recombine and again form the colourless ions. The photosensitivity is thus due to chemical reactions occurring in the glass.
24 Light Cloze Test ALight is a form of ______. In a piece of apparatus called a ______, light energy is converted to ______ energy, and in the process of photosynthesis it is converted to ______ energy. Animals get energy ______ from this process. Light travels in ______ lines, but it can be made to change direction in two ways by ______ and ______. When light strikes a mirror it is ______ and when it enters a glass block it is ______.Formative assessment:Questions have been suggested to promote discussion on each slide. Questions should be distributed to individuals and then class discussion. Light effects are very common so each section should draw out several real-life examples from the students.Summative assessment:A cloze test at the end should check that learning objectives have been met. This form of summative assessment I believe draws more useful enquiry from the students. They should be encouraged to think about the answers rather than look them up.
25 Light Cloze Test BLight, on being passed through a ______, is split up into its component colours. This process is known as ______ and the band of colours which is formed is called a ______. The colours are red, ______, ______, ______, ______, ______, ______. When all of these colours are recombined, ______ light is produced. This property of light was discovered by a scientist named ______. An example of real-life dispersion is a ______.
26 Light Cloze Test CAn experiment to show that light travels in ______ lines includes a light box, ______ sheets with a ______ in the centre, a piece of ______ used to align the sheets and a ______ as a source of light. If the sheets are not-aligned the viewer sees ______ and if they are aligned the viewer sees ______.To see the effect of shadows you require:______, ______ and a ______When the torch is turned on in a darkened environment the dark______ of the object appears on the ______.A light box, sheet, screen and a ______ ______ are required to show refraction from ______ to glass. To indicate ______, a triangular glass block known as a ______ is required which disperses the light and produces a ______ ______.This slide checks that the experiments are known
27 Light Cloze Test DA ______ glass is an example of a convex or ______ lens. This causes _____ rays to ______ at a point. The opposite type of lens is ______ in the middle and is know as a ______ lens. This causes light rays to ______ and is used in the glasses of ______ sighted people.If confronted by a tall wall, a ______ would enable you to see over it. They are more commonly found in ______ to see ______ the water surface. This works by placing ______ mirrors at an angle of ______.
28 Resources Images Information Sounds InformationDiagram & Info on Crooks RadiometerDid you know questions for lightSyllabus informationInfo on light, reflection & refractionScience Today, Physics TextbookSoundsFarm noises