11 Part 2 – Properties of Light Light travels in straight lines:Laser
12 Light travels VERY FAST – around 300,000 kilometres per second. At this speed it can go around the world 8 times in one second.
13 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.
14 We see things because they reflect light into our eyes: Homework
15 Luminous and non-luminous objects A luminous object is one that produces light.A non-luminous object is one that reflects light.Luminous objectsReflectors
16 ShadowsShadows are places where light is “blocked”:Rays of light
17 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
18 Part 3- Visible LightVisible light is the part of the EM spectrum that we as humans can detect with our eyes. It is not a single color; it is made up of a mixture of the seven colors 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.
19 The colors of visible light: RedOrangeYellowGreenBlueIndigoVioletSince the color a visible light wave appears is a product of the wavelength and frequency, color is a property of the wave.
20 Seeing ColorsColor is detected by cone cells in the retina of the eye. There are only 3 kinds of cone cells: red, green, and blue. Human’s see all the colors of the rainbow by adding together different amount of red, blue, and green.
21 Part 4 - Color AdditionWhite 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
22 Color AdditionPrimary colors of light: red, blue and green Add together to make all the colors of the visible spectrum. The colors they create when added together in full strength are called secondary colors of light: cyan, magenta, and yellow. When all three primary colors of light are added together they create white light.
23 Part 5 - Color Subtraction White light from the sun or from a light bulb illuminates objects. White light contains ALL the colors of light.Filters can be used to absorb out different colors of light:Red FilterMagenta Filter
24 Color SubtractionObjects that contain pigments appear colors depending on what colors of light are absorbed and what colors are reflected. There are three primary pigments that combine to make all the other colors of pigment in the world. Cyan, Magenta, and Yellow. When they combine they create the secondary pigments red, blue and green.
25 What color does it appear? The color an object appears depends on the colors of light it reflects…It acts just like the filters. We can predict the color an object will appear based on color subtraction.For example, a red book only reflects red light:HomeworkWhitelightOnly red light is reflected
26 A white hat would reflect all seven colors: A pair of purple trousers would reflect magenta light (and red and blue, as magenta is made up of red and blue):Magenta lightA white hat would reflect all seven colors:Whitelight
27 Using colored lightIf we look at a coloured object in coloured light we see something different. For example, consider a this outfit:Shirt looks redWhitelightShorts look blue
28 In different colors of light this outfit would look different: RedlightShirt looks redShorts look blackShirt looks blackBluelightShorts look blue
29 Some further examples: ObjectColor of lightColor object seems to beRed socksRedBlueBlackGreenBlue teddyGreen camelMagenta bookHomework
30 Color Subtraction with filters Color of filterColor absorbedColors ReflectedColor SeenRedGreenBlueCyanMagentaYellowRed and GreenCyan and MagentaYellow and GreenColor of filter
32 Part 6 - ShadowsWhenever light is blocked a shadow is created. If an object is near the light source the shadow will be larger. If the object is far from the light source the shadow will be smaller. A persons shadow will be the longest when the sun is farthest away and is at an angle (dusk and dawn). A person’s shadow will be the shortest at noon because the sun is as close as it can be and is directly over head.
33 Parts of a ShadowUmbra- The area directly behind the object where ALL light is blocked. Appears dark black. Penumbra- The area around the object where light is only partially blocked. Appears gray and fuzzy.
34 Colored ShadowsWhen the primary colors of light are ADDED together white light appears.When an object is placed in front of white light from color addition it will form 7 shadows.Primary Shadows:Magenta, Cyan and YellowSecondary shadows appear where the primary shadows overlap.Secondary Shadows:Red, Blue, Green, BlackMagenta = Green is blocked, so blue and red are reflected.Cyan = Red is blocked, so blue and green are reflected.Yellow = Blue is blocked, so red and green are reflected.Red = Blue and Green are blocked, and red is reflected.Blue = Red and Green are blocked, and blue is reflected.Green = Red and Blue are blocked, and green is reflected.Black = All light is blocked!