The Electromagnetic and Visible Spectra
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`The Physics Classroom(/) » Physics Tutorial(/class) » Light Waves and Color(/class/light) » The Electromagnetic and Visible
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`Spectra
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`Light Waves and Color - Lesson 2 - Color and Vision
`The Electromagnetic and Visible Spectra
`
`The Electromagnetic and Visible Spectra
`
`Visible Light and the Eye's Response(/class/light/Lesson-2/Visible-Light-and-the-Eye-s-Response)
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`As discussed in Unit 10 of The Physics Classroom Tutorial
`(http://www.physicsclassroom.com/Class/waves/u10l1c.cfm#emmech), electromagnetic
`waves are waves that are capable of traveling through a vacuum. Unlike mechanical waves
`that require a medium in order to transport their energy, electromagnetic waves are capable
`of transporting energy through the vacuum of outer space. Electromagnetic waves are
`produced by a vibrating electric charge and as such, they consist of both an electric and a
`magnetic component. The precise nature of such electromagnetic waves is not discussed in
`The Physics Classroom Tutorial. Nonetheless, there are a variety of statements that can be
`made about such waves.
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`Electromagnetic waves exist with an enormous range of frequencies. This continuous range of
`frequencies is known as the electromagnetic spectrum. The entire range of the spectrum is
`often broken into specific regions. The subdividing of the entire spectrum into smaller spectra
`is done mostly on the basis of how each region of electromagnetic waves interacts with matter.
`The diagram below depicts the electromagnetic spectrum and its various regions. The longer
`wavelength, lower frequency regions are located on the far left of the spectrum and the
`shorter wavelength, higher frequency regions are on the far right. Two very narrow regions
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`within the spectrum are the visible light region and the X-ray region. You are undoubtedly
`familiar with some of the other regions of the electromagnetic spectrum.
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`Visible Light Spectrum
`The focus of Lesson 2 will be upon the visible light region - the very narrow band of
`wavelengths located to the right of the infrared region and to the left of the ultraviolet region.
`Though electromagnetic waves exist in a vast range of wavelengths, our eyes are sensitive to
`only a very narrow band. Since this narrow band of wavelengths is the means by which humans
`see, we refer to it as the visible light spectrum. Normally when we use the term "light," we are
`referring to a type of electromagnetic wave that stimulates the retina of our eyes. In this sense,
`we are referring to visible light, a small spectrum from the enormous range of frequencies of
`electromagnetic radiation. This visible light region consists of a spectrum of wavelengths that
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`http://www.physicsclassroom.com/class/light/Lesson-2/The-Electromagnetic-and-Visible-Spectra
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`The Electromagnetic and Visible Spectra
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`range from approximately 700 nanometers (abbreviated nm) to approximately 400 nm.
`Expressed in more familiar units, the range of wavelengths extends from 7 x 10 meter to 4 x
`-7
`10 meter. This narrow band of visible light is affectionately known as ROYGBIV.
`-7
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`Each individual wavelength within the spectrum of visible light wavelengths is representative
`of a particular color. That is, when light of that particular wavelength strikes the retina of our
`eye, we perceive that specific color sensation. Isaac Newton showed that
`light shining through a prism will be separated into its different wavelengths
`(http://www.physicsclassroom.com/Class/refrn/u14l4a.cfm) and will thus
`show the various colors that visible light is comprised of. The separation of
`visible light into its different colors is known as dispersion. Each color is
`characteristic of a distinct wavelength; and different wavelengths of light waves will bend
`varying amounts upon passage through a prism. For these reasons, visible light is dispersed
`upon passage through a prism. Dispersion of visible light produces the colors red (R), orange
`(O), yellow (Y), green (G), blue (B), and violet (V). It is because of this that visible light is
`sometimes referred to as ROY G. BIV. (Incidentally, the indigo is not actually observed in the
`spectrum but is traditionally added to the list so that there is a vowel in Roy's last name.) The
`red wavelengths of light are the longer wavelengths and the violet wavelengths of light are the
`shorter wavelengths. Between red and violet, there is a continuous range or spectrum of
`wavelengths. The visible light spectrum is shown in the diagram below.
`
`When all the wavelengths of the visible light spectrum strike your eye at the same time, white
`is perceived. The sensation of white is not the result of a single color of light. Rather, the
`sensation of white is the result of a mixture of two or more colors of light. Thus, visible light -
`the mix of ROYGBIV - is sometimes referred to as white light. Technically speaking, white is
`not a color at all - at least not in the sense that there is a light wave with a wavelength that is
`characteristic of white. Rather, white is the combination of all the colors of the visible light
`spectrum. If all the wavelengths of the visible light spectrum give the appearance of white,
`then none of the wavelengths would lead to the appearance of black. Once more, black is not
`actually a color. Technically speaking, black is merely the absence of the wavelengths of the
`visible light spectrum. So when you are in a room with no lights and everything around you
`appears black, it means that there are no wavelengths of visible light striking your eye as you
`sight at the surroundings.
`
`Investigate!
`The widget below matches the wavelength of light (in nanometers) to a particular color of
`light. Explore by entering various values between 400 nanometers and 700 nanometers.
`Values outside this range are not visible and therefore not associated with human-perceived
`color.
`
`Match a Wavelength of Light to a Color
`
`Enter the wavelength of a light wave (between 400 nm and 700 nm)
`
`and then click on the Match to Color button.
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`Wavelength (nm)
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`600
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`Match to Color
`
`(http://www.wolframalpha.com)
`
`Check Your Understanding
`1. A light wave is an electromagnetic wave that has both an electric and magnetic component
`associated with it. Electromagnetic waves are often distinguished from mechanical waves. The
`distinction is based on the fact that electromagnetic waves ______.
`
`a. can travel through materials and mechanical waves cannot
`
`b. come in a range of frequencies and mechanical waves exist with only certain
`frequencies
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`c. can travel through a region void of matter and mechanical waves cannot
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`d. electromagnetic waves cannot transport energy and mechanical waves can
`transport energy
`
`e. electromagnetic waves have an infinite speed and mechanical waves have a finite
`speed
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`See Answer
`
`http://www.physicsclassroom.com/class/light/Lesson-2/The-Electromagnetic-and-Visible-Spectra
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`10/9/2015
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`
`The Electromagnetic and Visible Spectra
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`2. Consider the electromagnetic spectrum as you answer these three questions.
`
`a. Which region of the electromagnetic spectrum has the highest frequency?
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`b. Which region of the electromagnetic spectrum has the longest wavelength?
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`c. Which region of the electromagnetic spectrum will travel with the fastest speed?
`
`See Answer
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`3. Consider the visible light spectrum as you answer these two questions.
`
`a. Which color of the visible light spectrum has the greatest frequency?
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`b. Which color of the visible light spectrum has the greatest wavelength?
`
`See Answer
`
`Next Section:
`Visible Light and the Eye's Response(/class/light/Lesson-2/Visible-Light-and-the-Eye-s-Response)
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`Jump To Next Lesson:
`Anatomy of a Two-Point Source Interference Pattern(/class/light/Lesson-3/Anatomy-of-a-Two-Point-
`Source-Interference-Pattern)
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