Presentation on theme: "Light and Color Chapters 27 – 28"— Presentation transcript:
1 Light and Color Chapters 27 – 28 Created by N. Ferreira with the help of A, Kirby
2 27.1 Early Concepts of Light Initially, light was thought to be made of tiny particles because light moves in straight lines.Later, the wave theory of light was developed. The evidence that supported the wave theory was that light will spread out (diffract).Currently, light is believed to have a dual nature - part particle, part wave
3 27.2 The Speed of LightThe speed of light is 3 x 108 m/s or 187,000mi/s.The speed of light is constant when it travels through one type of medium. Light travels faster in air than in water.Light takes 8 minutes to travel from the sun to the earth.
4 27.3 Electromagnetic Waves Light is energy that is emitted by accelerating charges – often electrons in atoms.The energy travels in a wave that is partly electric and partly magnetic. These waves are called electromagnetic waves.The range of electromagnetic waves is called the electromagnetic spectrum.
5 The Electromagnetic Spectrum All of the electromagnetic waves are the same in nature, differ only in the wavelength and frequencySaying to help you remember the EM spectrum:Ronald McDonald Is Very Ugly X-tra GrossNotice: Visible light makes up very small portion of the EM spectrum
6 Red light is the lowest frequency of light we can see. Violet light is the highest frequency light we can see.Infrared waves are lower in frequency than red light. Heat lamps give off infrared radiation.Ultraviolet waves are higher in frequency than violet light. UV rays from the sun cause sunburn
7 Transparent, Opaque and Shiny Transparent materials allow light to pass throughOpaque materials do not allow light to pass through. When light hits opaque materials, the light energy is converted into heat.The electrons of shiny materials, like metals, are too far apart to transfer energy so the energy is re-emitted as light.
8 Shadows Shadows are places where light rays do not reach. Two types of shadows:1) Umbra total shadow where all light is blocked2) Penumbra partial shadowSolar eclipses do not occur as often as lunar eclipses because the sun is much larger than the moon.
9 27.7 Polarization Polarized light travels in only one direction. Unpolarized light travels in many directions.A polarizing filter polarizes light.Light passes through a pair of polarizing filters when their axes are aligned, but when the filters are crossed at right angles, no light will pass through.
11 28.1 The Color SpectrumSunlight is a mixture of all the colors of the rainbow.Sunlight is an example of white light. White is not a color, but a combination of all colors.Black is also not a color, but is the absence of light. An object appears black when all the frequencies of light are absorbed.
12 28.2 Color by ReflectionMost material absorb light of some frequencies and reflect the rest. We see the reflected light.
13 Reflection and LightIf a material absorbs all the light that shines on it and reflects none it appears blackThe appearance of a colored object depends on the kind of light used.A candle flame emits light that is deficient in higher frequencies; it emits a yellowish light.An incandescent lamp lamp emits light of all the visible frequences but richer toward the lower enhancing reds.A fluorescent lamp is richer in higher frequencies, so blues are enhanced.
14 28.3 Color by TransmissionThe color of a transparent object depends on the color of light it transmits.A piece of blue glass will appear blue because it absorbs all colors of light except blue.The material that selectively absorbs colored light is known as pigment.
15 28.4 SunlightYellow – green light is the brightest part of sunlight. This is the color human eyes are the most sensitive too.When light enters a new medium its color does not change because its frequency does not change.What changes is the speed and wavelength of the light.
16 28.5 Mixing Colored LightLight of all the visible frequencies mixed together produces white light.White light can also be produced by mixing red, blue, and green light. Red, blue, and green are the 3 additive primary colors of light.Color T.V.s produce all the colors we perceive by combing red, blue, and green light in a variety of ways.
17 Adding Primary Colors Red + Green = Yellow Red + Blue = Magenta (Purple)Blue+ Green = Cyan (Aqua)Red + Blue + Green = White
18 28.6 Complementary ColorsWhen two different colors add together to form white, they are called complementary colors.Yellow Blue = White(Red + Green)Magenta Green = White(Blue + Red)Cyan Red = White(Blue + Green)Yellow and blue are complementary colorsMagenta and green are complementary colorsCyan and red are complementary colors
19 28.7 Mixing Color PigmentWhen pigments are mixed to produce a different color this is called color mixing by subtraction.The three primary subtractive colors are1) magenta2) yellow3) cyan
20 28.8 Why the Sky is BlueSmall particles (N2 & O2) scatter light of high frequency such as blue
21 28.9 Why Sunsets are RedWhen the sun sets, sunlight reaches us through a long path so light of long wavelengths (red) reach us
22 Why Clouds are WhiteClouds are white because water molecules in the clouds scatter different colors of light.
23 28.11 The Atomic Color CodeEvery element has its own characteristic color when made to emit light.The glow of each atom is unlike the glow of any other element.When light from a glowing element is analyzed through a spectroscope, it is found that the colors are a composite of a variety of different frequencies.