Let there be light!
From the moment we get up in the morning to the moment close our eyes to go to sleep, we see objects, images and colors. Everything we see depends on light. Think of all the things you can appreciate because of light: crayon drawings, finger and oil paintings, computer graphics, sunsets, shooting stars, rainbows.
The way we think about light has changed through the course of history, from the theories of the ancient Greeks to the theories of Albert Einstein. We encounter light in many devices, such as incandescent bulbs, fluorescent bulbs, lasers, lightning bugs and even the sun. Each object uses a different technique to generate photons. According to Dictionary.com, a photon is “the subatomic particle that carries the electromagnetic force and is the quantum of electromagnetic radiation.”
The particle theory of light involves photons, while the wave theory of light suggests that light is a wave. Research these two theories. Compare the information you find and create an oral report to share with your class. Remember to document your sources.
Colored waves of energy
Light waves are waves of energy. The amount of energy in a light wave is proportionally related to its frequency. In other words, high frequency light has high energy and low frequency light has low energy. Gamma rays have the most energy, and radio waves have the least. Of visible light, violet has the most energy and red the least.
Light also vibrates and travels at different speeds. Light waves move through a vacuum at their maximum speed, 300,000 kilometers per second or 186,000 miles per second. Light waves slow down when they travel inside substances, such as air, water, glass or a diamond. The way different substances affect the speed at which light travels is key to understanding the bending of light, or refraction.
Producing a Photon
Any light that you see is made up of a collection of one or more photons circulating through space as electromagnetic waves. In total darkness, our eyes are actually able to sense single photons, but generally what we see in our daily lives comes to us in the form of zillions of photons produced by light sources and reflected off objects. If you look around you right now, there is probably a light source in the room producing photons, and objects in the room that reflect those photons. Your eyes absorb some of the photons flowing through the room, and that is how you see.
Bring on the heat
Probably the most common way to energize atoms is with heat, and this is the basis of incandescence. Red is the lowest-energy visible light, so in a red-hot object the atoms are just getting enough energy to begin emitting light that we can see. Once you apply enough heat to cause white light, you are energizing so many different electrons in so many different ways that all of the colors are being generated -- they all mix together to look white. Heat is the most common way we see light being generated -- a normal 75-watt incandescent bulb is generating light by using electricity to create heat. However, there are lots of other ways to generate light:
Making colors
Visible light is light that can be perceived by the human eye. When you look at the visible light of the sun, it appears to be colorless, which we call white. And although we can see this light, white is not considered to be part of the visible spectrum. This is because white light is not the light of a single color, or frequency. Instead, it is made up of many color frequencies.
Look up the following terms to understand what we are seeing when we see light and color.
Source: All information on this page is taken from "How Light Works" by Craig Freudenrich, Ph.D. For more information, log on to HowStuffWorks.com.
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