Presentation on theme: "Light travels in straight lines:"— Presentation transcript:
1 Light travels in straight lines: Properties of LightLight travels in straight lines:Laser
2 Light travels VERY FAST – around 300,000 kilometres per second. At this speed it can go around the world 8 times in one second.
3 Light travels much faster than sound. For example: Thunder and lightning start at the same time, but we will see the lightning first.2) When a starting pistol is fired we see the smoke first and then hear the bang.
4 We see things because they reflect light into our eyes: Homework
5 Luminous and non-luminous objects A luminous object is one that produces light.A non-luminous object is one that reflects light.Luminous objectsReflectors
6 ShadowsShadows are places where light is “blocked”:Rays of light
7 Properties of Light summary Light travels in straight linesLight travels much faster than soundWe see things because they reflect light into our eyesShadows are formed when light is blocked by an object
8 Reflection Reflection from a mirror: Mirror Normal Angle of incidence Incident rayReflected rayAngle of incidenceAngle of reflectionMirror
9 Angle of incidence = Angle of reflection The Law of ReflectionAngle of incidence = Angle of reflectionIn other words, light gets reflected from a surface at ____ _____ angle it hits it.The same !!!
10 Clear vs. Diffuse Reflection Smooth, shiny surfaces have a clear reflection:Rough, dull surfaces have a diffuse reflection.Diffuse reflection is when light is scattered in different directions
11 Using mirrorsTwo examples:2) A car headlight1) A periscope
12 Refraction through a glass block: Wave slows down and bends towards the normal due to entering a more dense mediumWave slows down but is not bent, due to entering along the normalWave speeds up and bends away from the normal due to entering a less dense medium
13 Words – speed up, water, air, bent, medium RefractionRefraction is when waves ____ __ or slow down due to travelling in a different _________. A medium is something that waves will travel through. When a pen is placed in water it looks like this:In this case the light rays are slowed down by the water and are _____, causing the pen to look odd. The two mediums in this example are ______ and _______.Words – speed up, water, air, bent, medium
15 ColourWhite light is not a single colour; it is made up of a mixture of the seven colours of the rainbow.We can demonstrate this by splitting white light with a prism:This is how rainbows are formed: sunlight is “split up” by raindrops.
16 The colours of the rainbow: RedOrangeYellowGreenBlueIndigoViolet
18 Adding coloursWhite light can be split up to make separate colours. These colours can be added together again.The primary colours of light are red, blue and green:Adding blue and red makes magenta (purple)Adding blue and green makes cyan (light blue)Adding red and green makes yellowAdding all three makes white again
19 Only red light is reflected Seeing colourThe colour an object appears depends on the colours of light it reflects.For example, a red book only reflects red light:HomeworkWhitelightOnly red light is reflected
20 A white hat would reflect all seven colours: A pair of purple trousers would reflect purple light (and red and blue, as purple is made up of red and blue):Purple lightA white hat would reflect all seven colours:Whitelight
21 Using coloured lightIf we look at a coloured object in coloured light we see something different. For example, consider a football kit:Shirt looks redWhitelightShorts look blue
22 In different colours of light this kit would look different: RedlightShirt looks redShorts look blackShirt looks blackBluelightShorts look blue
23 Some further examples: ObjectColour of lightColour object seems to beRed socksRedBlueBlackGreenBlue teddyGreen camelMagenta bookHomework
24 Using filters Red Filter Filters can be used to “block” out different colours of light:Red FilterMagenta Filter