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electromagnetic radiation     visible light     wavelength     photons     refraction     reflection     color     prism     mirror     vacuum     speed of light     lens     luminous   absorb    color spectrum    translucent    transparent

IMPORTANT NOTE:
Our class researched the online sources
 Bill Nye the Science Guy®, Fact Monster, How Stuff Works, NASA,  Physics4Kids, and Wikipedia
What is shown on this page are our study notes from what we learned.
Please visit the actual sites for accurate, complete information!

What is light?  |  What is electromagnetic radiation?  |  What are photons?  |  What is the speed of light?  |  What is refraction?  |  What is reflection?  |  What is color?  |  Links

What is light?
Light is electromagnetic radiation that has a wavelength that is visible. It is visible light -- the light that humans can see.

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Graphic from www.Wikipedia.com 

What is electromagnetic radiation?
Visible light is only one small type of electromagnetic radiation. Electromagnetic radiation has different wavelengths. Some radiation, such as radio waves, has very long wavelengths. Visible light is near the middle of the spectrum. Gamma rays and cosmic rays are at the other end of the spectrum and have very small wavelengths. Other examples are radio, microwaves, infrared and ultraviolet light, X-rays and gamma-rays.1 Watch BrainPop Movie  More..  Chart..  Quiz..

 

The key thing to remember is that electromagnetic radiation, including visible light, is energy.

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What are photons?
There are very small particles called photons moving in the wave pattern. The wavelength determines the type of EM radiation, and the number of particles tells you how much radiation there is. A lot of photons give a brighter, more intense type of light. Fewer photons give a very dim and less intense light. When you use the dimmer switch on the wall, you are decreasing the number of photons sent from the light bulb. The type of light is the same while the amount has changed.

The key thing to remember is that the wavelength determines EM type, and the number of photons determines how much. Wavelength = EM type. Number of Photons = amount.

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What is the speed of light?
Light is the fastest thing in the universe. It is almost a million times faster than sound. That is why we see lightning before we hear the thunder that comes with it. Scientists have determined that the speed of light in a vacuum is almost 300 million meters per second (186,000 miles per second). It takes the Sun's light about eight minutes to reach earth. It takes the Sun's light over four years to get to the nearest star. It would take light over 100,000 years to get from one side of our galaxy to the other side. All of those values are light moving through a vacuum. You can slow light down in substances such as the atmosphere, water, or a diamond. Light moves at about 124,000,000 meters per second (less than half the speed in a vacuum) in a diamond.

The key thing to remember is that light is the fastest thing in the universe. The speed of light can change as it goes through something.

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What is refraction?
Light travels in straight lines called light rays. Light continues to travel in straight lines until it hits other media or objects. Refraction is the change in direction of a wave due to a change in its speed. This is most commonly seen when a wave passes from one medium to another, such as air to water. Photo from www.Britannica.com

Refraction has many useful applications in optics and technology. A lens uses refraction to form an image of an object for many different purposes, such as magnification. A prism uses refraction to form a spectrum of colors from an incident beam of light. Convex lenses focus light. Concave lenses spread out light rays. Refraction can also play an important role in the formation of a mirage and other optical illusions.

When light travels straight through an object, that object is transparent (such as a window). When light travels through an object, but the light rays do not go straight and the object is blurry to the eye, that object is translucent (such as wax paper). When light cannot travel through an object, that object is opaque (like a wall).

The key thing to remember is that refraction is a change in light's direction, which we can put to use in many applications such as lenses, magnifiers, cameras, telescopes, projectors, etc.

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What is reflection?
When a light ray hits an object and bounces off, it is reflection. When you think of reflection, think about mirrors. They reflect all of the light wavelengths. That is the reason you can see yourself.

The sun and objects like light bulbs give off their own light. Those objects are luminous. Even though the moon may seem to glow, it is not luminous. The moon is bright because it reflects the light from the sun.

The key thing to remember is that light reflection is the light that bounces off.

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What is color?
We see color because different objects reflect different light frequencies. Green plants are green because they absorb all of the colors of the visible spectrum except the green color (they reflect the green color). A red wall is red to your eyes because it is not absorbing light from the red wavelengths, it is reflecting the red. Mirrors reflect all of the colors of visible light.

Since the colors that compose sunlight or white light have different wavelengths, the speed at which they travel through a medium such as glass differs; red light, having the longest wavelength, travels more rapidly through glass than blue light, which has a shorter wavelength. Therefore, when white light passes through a glass prism, it is separated into a band of colors called a spectrum. The visible colors from shortest to longest wavelength are: violet, blue, green, yellow, orange, and red.2

Find out more! Making colors.., Chart.., Why is the sky blue?, What causes a rainbow? Link to NASA graphic..

 

Light that is absorbed is changed to thermal energy. That is why in the summer we feel so much hotter when the sun strikes our black shirt, than when the sun strikes our white shirt.

 

The key thing to remember is that the color of an object depends on the wavelengths of the light it reflects. Black and white are not true colors; black results from the absence of color, and white results from the presence of all colors mixed together.

 

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The Bottom Line

  • Visible light is electromagnetic radiation that humans can see.

  • Light travels in a straight line unless it hits something or is pulled on by gravity.

  • When light hits something, it can be bent (refraction), bounced (reflection) or absorbed.

  • White light is made up of all the colors mixed together.

  • The color of an object comes from the color of light it reflects; the other colors of light are absorbed by the object.3

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 Related Links

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Bibliography

1  The Imagine Team, NASA, "Electromagnetic Spectrum," March, 2006, http://imagine.gsfc.nasa.gov/docs/science/know_l1/emspectrum.html (accessed February 17, 2007).

 

2 Craig Freudenrich, Ph.D.,  "How Light Works,"  July 10, 2000, http://science.howstuffworks.com/light.htm (accessed February 10, 2007).
 

3 Bill Nye the Science Guy®, "Light Optics" and "Light and Color," 2005, http://www.billnye.com/ (accessed February 17, 2007).

 

Andrew Rader, "Light and Optics". 2007. http://www.physics4kids.com/files/light_intro.html (accessed February 17, 2007).

 

"color: The Visible Spectrum." The Columbia Electronic Encyclopedia.
© 1994, 2000-2006, on Fact Monster.
© 2000–2007 Pearson Education, publishing as Fact Monster.
17 Feb. 2007 <http://www.factmonster.com/ce6/sci/A0857451.html>.

 

"illusion." Online Photograph. Encyclopædia Britannica Online. 2007.  http://www.britannica.com/eb/art-92362 (accessed April 15, 2007).

 

Wikipedia contributors, "Light," Wikipedia, The Free Encyclopedia, http://en.wikipedia.org/w/index.php?title=Light&oldid=108203996 (accessed February 17, 2007).

 

Citing: This webpage is a location for our investigation and study notes. We are not experts or scientists; we are students. Please do not cite!

 

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