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wavelength (nm) 450 400 600 580 550 700 Additive Colour Theory of Light radio waves microwaves The additive colour theory of light states that white light is composed of different colours (wavelengths) of light. It is possible to produce white light by combining only three colours. One such combination is red, green, and blue. These three colours of light are known as primary colours. If you mix correct amounts of all three primary colours of light, you will make white light (Figure 10.18(a)). If you mix only two of the primary colours together, you will make a secondary colour. The secondary colours of light for red, green, and blue are magenta, yellow, and cyan as shown in Figure 10.18(b). infrared ultraviolet X-rays gamma rays Figure 10.17 The visible spectrum has red light at one end, violet light at the other end, and all the other colours in between. Red light has a relatively long wavelength of 700 nm (nanometres) while violet light has a shorter wavelength of about 400 nm. A nanometre is one-billionth of a metre, so 700 nm is 0.000 000 7 m. white light green light red light blue light (a) (b) magenta yellow Figure 10.18 (a) All three primary colours together produce white light. (b)The three primary colours of light are red, green, and blue. When paired, they can create three secondary colours: magenta, yellow, and cyan. cyan visible light Light is part of the electromagnetic spectrum and travels in waves. 387
Figure 10.19 The subtractive theory applies to pigments and dyes. It is the opposite of the additive theory of light. Suggested Activity • D3 Quick Lab on page 389 (a) (b) (c) white light red green blue cyan Figure 10.20 How subtractive colours reflect light Take It Further Inkjet printers employ subtractive colour technology. Refill ink cartridges come in cyan, magenta, and yellow. Find out more about how inkjet printers apply the three inks to a page to create all possible colours. Begin your research at ScienceSource. 388 UNIT D Light and Geometric Optics Subtractive Colour Theory of Light When a light wave strikes an object, some wavelengths of light reflect, which means that they bounce off the object. Other wavelengths are absorbed by the object. The colour you see when you look at an object depends on the wavelengths that are reflected. For example, a red rose reflects red wavelengths of light and absorbs other colours. According to the subtractive colour theory of light, coloured matter selectively absorbs different colours or wavelengths of light. The colours that are absorbed are “subtracted” from the reflected light that is seen by the eye. A black object absorbs all colours, whereas a white object reflects all colours. A blue object reflects blue and absorbs all other colours. The primary and secondary colours of light for the subtractive theory are opposite to the colours of the additive theory (Figure 10.19). Cyan, magenta, and yellow are the primary subtractive colours, while red, green, and blue are the secondary subtractive colours. It is important to remember that the subtractive theory of light applies to pigments and the colours that they absorb. A pigment is a powder used to colour substances. If a colour is absorbed, it will not make it to your eye. You only see the reflected colours (Figure 10.20). Paint and pigment manufacturers mix all three of the primary subtractive colours in varying degrees to make any range of colours reflect from a surface. The printing press that produced this book used the three primary subtractive colours to create all the pictures you see. white light green blue red green blue magenta Learning Checkpoint white light red blue red green blue 1. What property of a light wave determines the colour of the light? yellow 2. List the six general categories of colour from the longest wavelength to the shortest wavelength. 3. What is the visible spectrum? 4. What does the additive colour theory of light state? 5. What does the subtractive colour theory of light state? red green
Page 1 and 2: UNIT D Light travels through colour
Page 3 and 4: Exploring These doctors are examini
Page 5 and 6: 0 Light is part of the electromagne
Page 7 and 8: 10.1 Here is a summary of what you
Page 9 and 10: During Reading Graphics Support Tex
Page 11 and 12: Uses of the Electromagnetic Spectru
Page 13: light source white light prism scre
Page 17 and 18: DI Key Activity D4 Quick Lab Seeing
Page 21 and 22: WORDS MATTER “Incandescent” has
Page 23 and 24: During Reading Get the Picture Even
Page 25 and 26: Figure 10.36 Plasma screens use flu
Page 27 and 28: D7 Quick Lab Analyzing Light Source
Page 31 and 32: Figure 10.42 Light rays travel away
Page 33 and 34: Suggested Activities • • D10 Qu
Page 35 and 36: D11 Inquiry Activity Shadows and Ra
Page 37 and 38: Investigating 410 UNIT D Light and
Page 39 and 40: 10 CHAPTER REVIEW ACHIEVEMENT CHART
Page 41 and 42: 11 Ray diagrams model the behaviour
Page 43 and 44: 11.1 Mirrors Here is a summary of w
Page 45 and 46: During Reading Diagrams Require Spe
Page 47 and 48: Suggested Activity • D16 Problem-
Page 49 and 50: 422 object ray 1 ray 2 image Figure
Page 51 and 52: Practice Problems 1. A microscope p
Page 53 and 54: Figure 11.16 Parallel light rays ap
Page 55 and 56: D13 Quick Lab Plane Mirror Reflecti
Page 57 and 58: DI Key Activity D15 Inquiry Activit
Page 59 and 60: D16 Problem-Solving Activity Laser
Page 63 and 64: Figure 11.30 The spoon appears to b
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Practice Problems 1. The speed of l
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Figure 11.36 This diamond is colour
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Suggested Activity • D19 Inquiry
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D18 Inquiry Activity Refraction Mea
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D20 Design a Lab Transmitting Light
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11.3 Lenses Here is a summary of wh
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WORDS MATTER The word “lens” is
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object ray 2 F ray 1 image Figure 1
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Practice Problems 1. A convex lens
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D23 Skill Builder Activity Drawing
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D25 Inquiry Activity Convex Lens Im
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11.3 CHECK and REFLECT Key Concept
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11 CHAPTER REVIEW ACHIEVEMENT CHART
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2 Optical devices help us see farth
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12.1 Here is a summary of what you
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WORDS MATTER “Pupil” is derived
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(a) near-sightedness (b) near-sight
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(a) (b) Figure 12.17 (a) Loss of th
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D28 Inquiry Activity Sheep Eye Diss
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DI Key Activity CASE STUDY D29 STSE
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12.2 Here is a summary of what you
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Figure 12.24 This portable imaging
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Suggested STSE Activity • D34 Dec
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During Writing Evaluating Informati
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WORDS MATTER The word “laser” i
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Figure 12.39 Long rows of solar cel
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D33 STSE Decision-Making Analysis S
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12.2 CHECK and REFLECT Key Concept
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12 CHAPTER REVIEW ACHIEVEMENT CHART
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D UNIT • Electromagnetic spectrum
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D UNIT Task How Much Light Is Too M
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D UNIT Review Key Terms Review 1. C
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D UNIT Review (continued) 35. (a) D
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D UNIT Review (continued) 62. Descr
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