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Light & the Electromagnetic Spectrum Chapter 25 25-1 Electromagnetic Waves I can describe the nature of an electromagnetic wave. I can explain how electromagnetic waves differ from other waves. Nature of an Electromagnetic Wave (EM) EM waves consist of both an electric field and a magnetic field. There is a push or pull of charged particles and magnets. Travel as transverse waves, fields are at right angles to the direction of motion of the wave. Nature of EM Waves Carry energy from one place to another. Matter does NOT vibrate, the electric and magnetic fields vibrate. Can travel without a medium. Production and Transmission of Electromagnetic Waves Atom: nucleus with protons and neutrons surrounded by electrons Electrons are constantly moving. Electrons are negatively charged particles that produce the electric and magnetic fields. Production of EM Waves Electrons move back and forth creating electric and magnetic fields that move back and forth (vibrate). The source of all electromagnetic waves is charge that is changing speed or direction. Visible Light Visible Light is produced by electrons jumping between different positions in an atom. Electrons gain energy, jump energy levels, fall back down and release energy. Types of Electromagnetic Waves Light, X-rays, Gamma rays Speed of all EM waves is the same: 300,000,000 m/s in a vacuum = speed of light Light travels slower in air and glass. Nothing in the universe travels faster than light. 25-1 Electromagnetic Waves I can describe the nature of an electromagnetic wave. I can explain how electromagnetic waves differ from other waves. Book Work Electromagnetic Wave Modulation 25.1 Section Review Page 645 # 1-5 25.1 Worksheet Electromagnetic Spectrum 25-2 The Electromagnetic Spectrum I can identify the parts of the electromagnetic spectrum. I can describe the uses of electromagnetic waves of different frequencies. I can explain the relationship between wavelength and frequency. EM Waves EM waves are arranged in order of wavelength and frequency in what is known as the electromagnetic spectrum. Waves with short wavelengths have high frequencies, because they all travel at the same speed both wavelength and frequency changes. Let’s make a poster For the assigned type of EM wave include: Name of type of wave energy Where does it come from Where it falls in the EM spectrum Uses of the energy Dangers of the energy Two interesting facts EM waves The amount of energy increases when frequency increases. The visible section is just a small region with all the colors. Radio Waves Lowest frequencies Longest wavelength Not the same as sound waves. Radio waves transmit information from the antenna of a broadcasting station to the antenna on your radio or television Radio Waves Modulation - the radio waves vary in either amplitude or frequency. AM = amplitude modulation FM = frequency modulation Sent through the air as electrical signals and in a pattern of changes in amplitude or frequency. Once picked up by TV/Radio they are changed back into their original form. Radio Waves Most sound portions of TV are carried as AM waves and most pictures are carried as FM waves. Can be disturbed by obstacles or weather conditions. TV cables protect the waves from interferences. Radio Waves Medicine: can vibrate parts of the brain to look at it without harming the cells – called magnetic resonance imaging. (MRI) Astronomy: used in telescopes because they can travel through space. MRI of the Brain Microwaves Highest frequency radio waves. Advantage: Heats food in short amount of time without heating the dish. Water and molecules in food absorb the energy (heat) from microwaves but dishes do not. Metals can absorb the energy – that is why you do not put metal in the microwave oven. They are also used in cell phones and weather forecasting. Microwave use: Radar Short wavelength microwaves are used in radar. Radar = radio detecting and ranging Used to locate objects and monitor speed. Works just like sonar Monitors positions of airplanes, ships at sea, satellites orbiting the earth, track storms Infrared Rays Infrared rays have slightly lower frequencies than visible light. Not seen but felt as heat. 50% of the suns rays are infrared All objects give off infrared rays, the amount depends on the temperature of the object. Infrared Rays Warm objects give off infrared rays. Cool objects absorb infrared rays and become warmer. Infrared camera take pictures of heat instead of light so can be used at night. Medicine: unhealthy tissue becomes hotter than healthy tissue. Can determine if art is real or fake by looking at paints. Visible Spectrum Light you can see = visible light Half of the energy given off by the sun is in the form of visible light. Visible light is used when plants make food (photosynthesis). Ultraviolet Rays Ultraviolet rays – frequency just higher than visible light Have enough energy to kill living cells. Used to kill germs in hospitals and destroy bacteria and preserve food. Ultraviolet Rays (UV) Humans can not see them but many insects can. They are what cause sunburn. Over exposure to UV rays can cause serious damage to the skin, eyes and immune system. Ozone in the atmosphere absorbs most of the sun’s damaging UV rays before they reach the earth. X-rays X-rays with frequencies just above UV rays Enough energy to pass easily through many materials, including skin. Denser material absorb x-rays. Bones absorb x-rays and on the pictures show up as white areas. X-rays Even though useful in medical diagnosis, they have a potential health hazard. Large amounts of x-rays over a lifetime can cause defects in cells. Gamma Rays Gamma rays – highest frequency and shortest wavelengths Can go through 3 meters of concrete. Excessive exposure to gamma rays can cause severe illness. Gamma cameras can be used to detect injected fluid that emits gamma rays in the body. Let’s watch a video clip Electromagnetic Spectrum 25-2 The Electromagnetic Spectrum I can identify the parts of the electromagnetic spectrum. I can describe the uses of electromagnetic waves of different frequencies. I can explain the relationship between wavelength and frequency. Terms radio wave radar x-ray microwave gamma ray infrared ray visible light ultraviolet ray 25.2 Section Review Page 656 # 1-4 o 25.2 Worksheet 25-3 Visible Light I can distinguish between luminous and illuminated objects. I can describe incandescent, fluorescent, and neon light. I can explain the differences between hot and cool light. Visible Light Luminous objects – anything that can give off its own light Ex: sun, other stars, light bulbs, campfires, fireflies Visible Light Illuminated objects – an object that can be seen because it is lit up Ex: moon, desk, paper, people Luminous Objects Luminous objects can produce light in 3 different ways: 1. incandescent light 2. fluorescent light 3. neon light Incandescent Light Incandescent light – produced from heat Ordinary light bulbs are hot to touch after they have been on for a while. Light bulbs have tungsten metal inside of them that heats up and produces light energy Coils of a toaster over heat up and glow red hot Fluorescent Light Cooler light and uses less electricity than incandescent lights. Electrons hit gas molecules to lessen the pressure. Phosphors (coated on the inside of the light) absorb UV energy and start to glow, producing visible light. Fluorescent Light The color of fluorescent lights depend on the color of the phosphors. Phosphors are sometimes added to laundry detergents to make clothes appear whiter because sunlight makes them glow. Neon Lights Also cool light like fluorescent lights Electrons pass through different types of gases and produce light. Neon gas = bright red Mercury gas = greenish-blue Sodium gas = yellow-orange 25-3 Visible Light I can distinguish between luminous and illuminated objects. I can describe incandescent, fluorescent, and neon light. I can explain the differences between hot and cool light. Terms luminous object incandescent light illuminated object fluorescent light neon light 25.3 Section Review Page 658 # 1-4 25.3 Worksheet 26-4 Color I can account for the color of opaque, translucent, and transparent objects. I can predict which colors will be transmitted, reflected, or absorbed by various substances. I can distinguish between colors of light and colors of pigments. I can describe polarized light and its uses. Why do objects have color? White light is broken into its individual colors by wavelength. When light strikes any form of matter, the light can be transmitted, reflected, or absorbed. Transmitted Light Transparent - light is transmitted through it, objects are seen very clear. Translucent - light is transmitted through a substance that scatters the light, the image is unclear and lacks detail. Ex: water, glass, air Ex: wax paper, frosted glass Opaque – does not transmit light. Ex: block of wood, sheet of metal, black cloth The Color of Objects If an object does not allow any light to pass through it (opaque), the light is either reflected or absorbed. The color of an opaque object is the color it reflects. A red apple reflects red and absorbs all the other colors. Black and White White is the presence of all the colors of the visible spectrum. White objects reflect all colors. Black objects absorb all of the colors. Primary Colors of Light Primary colors can be mixed to produce light of any other color. Primary colors are red, blue, and green. Adding different amounts of each creates different colors. Red and green light mixed produce yellow. Paints are Pigments (not light) The primary colors of pigments are yellow, cyan, and magenta. When all 3 are mixed evenly, all colors are absorbed and result in black. Compare Pigments (not light) Pigments have a certain color because they can absorb only certain wavelengths of the visible spectrum. All the rest are reflected. All objects contain pigments. The color of an object is a result of the pigments it contains. Polarized Light and Filters Sunglasses that reduce glare use polarized filters. Light waves vibrate in different directions at the same time. A polarizing filter is made up of a large number of vertical slits. Light can only pass through a polarizing filter if they are vibrating the same as the slits. Polarized Light and Filters Polarized light is light that passes through the filter. The rest of the light is reflected or absorbed. Sunlight glare is mostly horizontal so sunglasses are vertically polarized. 26-4 Color I can account for the color of opaque, translucent, and transparent objects. I can predict which colors will be transmitted, reflected, or absorbed by various substances. I can distinguish between colors of light and colors of pigments. I can describe polarized light and its uses. Terms Transparent Translucent Opaque Polarized light 26.4 Section Review Page 684 # 1-5 26.4 Worksheet Chapter 25 Review – pg 664 Multiple Choice True or False 1-8 1-6 Concept Master 1, 3, 7, 8