# 7.6.a Students know visible light is a small band within a very broad electromagnetic spectrum.

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7.6.a Students know visible light is a small band within a very broad electromagnetic spectrum.

 Wave- a disturbance that transfers energy from place to place  Energy- the ability to do work  Disturbance is temporary- after wave is gone medium is calm again  Most waves require a medium to travel through  Medium- material a wave travels through  Examples of mediums: gases, liquids, solids  Waves that require a medium are mechanical waves

 A wave that doesn’t require a medium is an electromagnetic wave (example: light)  Key concept: Mechanical waves are produced when a source of energy causes a medium to vibrate  Vibration- repeated back-and-forth and up-and- down motion  When a vibration goes through a medium a wave results  Energy is needed to make a wave  When waves travel though a medium the medium does NOT travel with the waves

Key concept: The basic properties of all waves are amplitude, wavelength, frequency, and speed.

 Amplitude- maximum distance that the particles of the medium moves away from the rest position  Crest- high point of the wave  Trough- low point of the wave

Properties of Waves Wavelength- the distance between two corresponding parts of the wave (example: from crest to crest)

 Frequency- number of complete waves in a certain amount of time  Hertz-units we use when measuring frequency  Waves travel at different speeds  Speed- far the wave travels in a given amount of time  If the medium doesn’t change the speed doesn’t change

What Is an Electromagnetic Wave?  Key concept: An electromagnetic wave consists of vibrating electric and magnetic fields that move through space at the speed of light.

 They transfer energy without a medium  Electromagnetic waves- transfers electrical and magnetic energy  They are produced by charged particles  Every charged particle has an electric field surrounding it

 Electromagnetic radiation- energy that is transferred through space by electromagnetic waves  Electromagnetic waves travel at the speed of light (about 300,000 kilometers per second)  They transfer energy through a vacuum or empty space  When light travels through a medium it travels slower

What Is the Electromagnetic Spectrum?  The electromagnetic spectrum is the complete range of electromagnetic waves placed in order of increasing frequency.

Videos: Exploring Light and Color: The Electromagnetic Spectrum Exploring Light and Color: The Electromagnetic Spectrum Light: The Electromagnetic Spectrum Light: The Electromagnetic Spectrum

 More frequency means more energy  Radio waves- electromagnetic waves with the longest wavelengths and lowest frequencies (radio and TV)  Microwaves- electromagnetic waves with the shortest wavelengths and highest frequencies (microwaves and cell phones)  Infrared Rays- invisible heat (heat lamps)

 All e lectromagnetic waves travel at the same speed in a vacuum but at different wavelengths and different frequencies  As wavelength decreases frequencies increases  Waves with the longest wavelengths have the lowest frequencies  Waves with the shortest wavelengths have the highest frequencies

 Key concept: The electromagnetic spectrum is made up of radio waves, infrared rays, visible light, ultraviolet rays, X-rays, and gamma rays.

 Visible light- small band in the broad electromagnetic wave that you can see  Main colors of visible light- red, orange, yellow, green, blue, indigo, violet

 Ultraviolet rays- wavelengths just shorter than visible light  Ultraviolet rays carry more energy than visible light  Exposure to small amounts of ultraviolet rays can be healthy but too much can cause skin cancer

 X-rays- wavelengths just shorter than visible light  Has more energy than ultraviolet rays so x-rays can penetrate most things  Dense matter (like bone or teeth) absorbs x-rays and doesn't let them pass through  Gamma rays- shortest waves, most frequency, and most penetrating  Gamma rays are used to kill cancer inside the body

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