Section 17.6 Electromagnetic Waves and the Electromagnetic Spectrum
Electromagnetic Waves Can you name all the colors of the rainbow? Red, Orange, Yellow, Green, Blue, Indigo, Violet
Electromagnetic Waves Electromagnetic Waves Electromagnetic waves are transverse waves produced by the motion of electrically charged particles called photons. Electromagnetic waves do not require a medium and are therefore able to travel at the speed of light. The speed of light = 3 x 10 8 m/s (300,000,000 m/s)
Electromagnetic Waves At this speed it can go around the world 8 times in one second.
Electromagnetic Waves Intensity The intensity of light decreases as energy travel farther from the source The Waves of the Spectrum The different electromagnetic waves are arranged in the electromagnetic spectrum. The electromagnetic spectrum is arranged in order of increasing frequency and decreasing wavelength. The higher the frequency, the more energy per wave, and the more potentially harmful the wave is.
Electromagnetic Spectrum Low Energy High Energy
Electromagnetic Spectrum Each kind of wave is characterized by a range of increasing frequency from left to right. Radio Waves (Low Energy) Microwaves Infrared Rays Visible Light Ultraviolet rays X-Rays Gamma Rays (High Energy)
Radio Waves Radio waves are the lowest frequency and longest wavelength in the spectrum. They are used primarily for communications, such as cell phones, T.V. and radio transmissions, and cordless devices such as phones, speakers, etc.
Radio Waves Include AM and FM radio stations AM: Amplitude Modulation The frequency waves stay the same and the amplitude of the wave is varied
Radio Waves Include AM and FM radio stations FM: Frequency Modulation The amplitude waves stay the same and the frequency of the wave is varied.
Microwaves Microwaves are a type of radio wave. They are used in cell phones and microwave ovens. At normal levels, microwaves are harmless.
Infrared Infrared radiation transfers energy in the form of heat. Examples include heat lamps and the warmth from the sun. Special types of film and cameras can show infrared radiation.
Visible Light Visible light can be separated into 7 different colors From lowest frequency to highest, they follow the acronym: ROY G. BIV When all 7 colors are combined together they produce white light. When all 7 colors of the spectrum are absent, then the color black is produced.
Ultraviolet (U.V.) Rays Ultraviolet (U.V.) rays have applications in health and medicine, and in agriculture. U.V. rays are potentially dangerous at high levels or with prolonged exposure. U.V. rays can cause sunburns and skin cancer, and kill bacteria and healthy cells.
X-Rays X-Rays are used in medicine, industry, and transportation to make pictures of the inside of solid objects. X-rays are potentially dangerous at moderate levels. X-rays can penetrate many materials such as skin, muscle, and many fabrics
Gamma Rays Gamma radiation is high frequency waves which can be extremely dangerous. Gamma rays are used in the medical field to kill cancer cells and make pictures of the brain and in industrial situations as an inspection tool. Destructive radiation from nuclear explosions Gamma waves are the highest frequency and shortest wavelength in the spectrum.
Light Waves
Light and Materials Visible light is in the middle of the electromagnetic spectrum.
Movement of Light Waves ROY G. BIV (Red, orange, yellow, green, blue, indigo, violet) Red: Long wavelength : Low Frequency & Low Energy Violet: Short wavelength : High Frequency & High Energy
Movement of Light Waves Without light, nothing is visible How light behaves when it strikes an object depends on many factors, including the material the object is made of. Materials can be transparent, translucent, or opaque.
Transparent u A transparent material transmits light, which means it allows the light that strikes it to pass through it.
Transparent Examples: 1. Glass Beaker 2. Fish in Fishbowl 3. Window on bus
Translucent u Translucent material scatters light. You can see through the material, but the objects you see through do not look clear.
Translucent Examples: 1. Frosted windows 2. Wax Paper 3. Plastic Cups
Opaque u Material absorbs or reflects all of the light that strikes it.
Opaque Examples: 1. Wood 2. Metals 3. Rocks
Interactions with Light u When light encounters matter, some or all of the energy in the light can be transferred to the matter. u When light strikes a new medium, the light can be reflected, absorbed, or transmitted.
Reflection Reflection happens when light waves bounce off a surface
Absorption u Stopping light is called absorption u When light hits most objects, some of the light bounces off and the rest is absorbed. u What you see when you look at it is the light that bounces off of it. u Smooth shiny objects reflect most of the light. Dull objects absorb most of the light that hits them and reflects the rest.
Absorption
Absorption and Color Why is a black car hotter than a white car in the summer? ü A black car absorbs all wavelengths of light, absorbing the energy and turning it to heat. ü Remember light is energy. Heat is another form of energy. ü A white car reflects all wavelengths of light.
Transmission u Wavelengths that are not absorbed are transmitted u When light is transmitted, it can be refracted, polarized, or scattered.
17.6 Assessment Question #1 How are electromagnetic waves different from mechanical waves? Electromagnetic waves do not require a medium Question #2 What is the speed of light? 3 x 10 8 m/s
17.6 Assessment Question #3 How do electromagnetic waves differ from one another? Each kind of wave is characterized by a range of increasing frequency Question #4 What happens to the intensity of light as energy moves away from the light source? The intensity of light decreases
17.6 Assessment Question #5 Explain the differences between opaque, transparent, and translucent material. Name an example of each one. Opaque Absorbs or reflects all of the light Transparent Allows the light that strikes it to pass through it Translucent Translucent material scatters light
17.6 Assessment Question #6 List three things that can happen when a light wave enters a new medium. ü Reflected ü Absorbed ü Transmitted
Question #7 What color do you see of all the visible light is absorbed in a material? Black 17.6 Assessment
Question #8 What color do you see of all the visible light is reflected from the material? White 17.6 Assessment
17.6 Assessment Question #9 Why do black objects get hotter quicker than white objects? The color black absorbs all wavelengths of light, absorbing the energy and turning it to heat.
Waves Mechanical Electromagnetic Medium Solid, Liquid, Gas No Medium Transverse Transverse Longitudinal Surface 90 Motion Parallel Motion Circular Motion Electromagnetic Spectrum 3x10 8 m/s Trough Crest Rarefaction Compression Radio, Microwave, Infrared, Visible, UV, X-Ray, Gamma ROY G. BOV Sound 340 m/s
Waves