# Electromagnetic Waves The Electromagnetic Spectrum S 8 P

• Slides: 30

Electromagnetic Waves & The Electromagnetic Spectrum S 8 P 4 a S 8 P 4 d

Waves • Most electromagnetic waves are invisible • Detect the present of waves by what we can see, feel, or hear

Electromagnetic Waves • Electromagnetic waves are a disturbance that transfers energy through a field • You have a EM wave when the disturbance occurs in a electric or magnetic field rather than in a medium

Sources • The Sun is main source of EM waves and provides most of the energy for Earth! • Stars also can give off EM waves but their wave don’t always make it to earth because of the distance between the earth and stars • Humans use technology to give off EM waves

How they travel • Energy that moves in the form of EM waves is called radiation • Mechanical waves must have a medium whereas EM waves can travel without a medium-like in a vacuum • EM waves do not lose energy as they move so they can travel forever!

Vacuum • Sun waves travel ~150 million km to reach earth (93 million miles) • Rays from other galaxies can travel billions of years before reaching earth • Waves in a vacuum spread out and travel until something interferes • The further they travel, the more they will spread and the less waves in a area (which means less energy being transferred to the area in which the wave will encounter)

Speed • Travel at a constant speed and very fast (300, 000 km per second) • Sun rays take 8 minutes to reach Earth • This constant speed is called the speed of light

EM Waves and mediums • When EM waves encounters a medium, it will react with it just like a mechanical wave…they transfer energy to the medium • They will also reflect, refract, or diffract which causes the energy to change direction

Answer the following questions: 1. How are EM waves different from mechanical waves? 2. What are two sources of EM waves in Earth’s environment? 3. How can EM waves transfer energy differently in a material medium as compared to a vacuum? 4. What might be one cause of uneven heating in a microwave oven?

The Electromagnetic Spectrum S 8 P 4 a

Electromagnetic Waves Electromagnetic waves come in many wavelengths and frequencies. Each one is useful in different ways. http: //science. hq. nasa. gov/kids/imagers/ems/index. html

Electromagnetic Spectrum • The electromagnetic spectrum is the range of all EM frequencies • The EM spectrum is a smooth, gradual progression from the lowest frequencies to the highest (and wavelengths)

Radio Waves • Waves that have the longest wavelength, the lowest frequency, and lowest energy • Travel easily through the atmosphere and materials • Radio waves are broadcasted by a transmitter where a receiver picks up the signals and converts it to sound waves • Radio stations use different frequencies so they don’t get crossed

Radio Waves • Two ways to modulate radio wave is by changing the amplitude and varying the frequency • Amplitude is used for AM • Frequency is used for FM • Televisions also use radio waves…they use AM signals for the picture and FM for the sound

Microwaves • Have shorter wavelengths, higher frequencies, and higher energy than other radio waves • Important uses of microwaves are radars and cell phones • Radars (WWII) transmits microwaves, receives reflections, and converts it into visual images • Radar led to the invention of the microwave oven

Microwaves • Your cell phone is actually a radio transmitter and receiver that uses microwaves • Sends and receives signals from a tower and is where the signals come together and allow you to connect with other person

Infrared Light • Found between microwaves and visible light, is the type of EM waves most often associated with heat • You cannot see infrared light, but you can feel the results • Examples: Warming lights at restaurants and your toaster

Visible Light • Part of the EM spectrum that humans can see and is the smallest part of the spectrum • The longest wavelength is “red” and the shortest is “violet” • The visible light from the sun is white light (all wavelengths are combined)

Visible Light • The range of colors is called the visible spectrum

Visible Light used in many ways • Vision • Find food and other survival activities • Plants need it to make their food • Can you think of anything else?

Where does it come from? • Most of it comes from the sun • The production of light by materials at high temperatures is called incandescence • Other sources include: Lightening and Fire

Living things produce light • Luminescence is the production of light without the high temperatures needed for incandescence. • The production of light by living organisms is called bioluminescence. – Produce by chemical reactions and not intense heat – Insects, worms, fish, squid, jellyfish, bacteria, and fungi

Human produced visible light • First was fire • Electrical lighting in late 1800’s (used tungsten) was known as incandescent bulbs • Fluorescence bulbs • Use gas instead of a filament – Neon lights (diff gases produce diff colors) • LED’s uses a semiconductor that regulates electric current to produce light

LED’s • Light-emitting diodes • Idea came from the bioluminescence of animals • Light that produces little heat and uses almost all of its electrical energy to make light instead of thermal energy • Not easily broken

Ultraviolet Light (radiation) • Has frequencies above those of visible light and partially below those of x-rays • Carries more energy than visible light • Waves can damage skin and eyes (cause sunburn) • Used to: sterilize medical equipment, kill harmful bacteria, produce vitamin D, treat skin problems and other medical conditions

X-rays • Very high frequencies and energy • Produced by sun and stars • Pass through soft tissue but is absorbed in dense matter, like bones • Over exposure to x-rays can cause cancer • Lead can block these types of EM waves

Gamma Rays • Highest frequencies and energy of all the EM waves • Produced by sun and stars and some radioactive substances • Gamma rays kill normal cells and cause cancer cells to develop • However, doctors can use gamma rays to kill cancer cells and fight tumors when carefully controlled

Short Story • For homework: – Write a short story in which the characters use or are affected by each of the different kinds of EM waves – Complete on a separate sheet of paper because you will turn it in