Waves

    Light is energy. More specifically, light is a form of electromagnetic radiation. This means that light energy is emitted in the form of a wave. Light is neither the type of wave that you give your friend when he leaves your house nor the kind that crashes ashore at the beach; this type of wave is a method of transferring energy. The specifics of this model are very important to how we perceive light and color.

    A wave is defined, generally, as an undulating or oscillatory motion. This description is just a start to understand the type of wave that makes up light.

    In physics a wave is defined as a disturbance traveling through a medium by which energy is transferred from one particle to another without causing permanent displacement of the medium itself. To visualize what this definition is telling us, just think of a crowd at a sporting event doing "the wave." Each spectator watches as this man-made wave reaches his or her section, then stands up, raises his or her arms, and sits down. Now, imagine a stadium full of people doing "the wave" with a giant sheet covering them so that none of the spectators can be seen. To someone watching such an event it would appear that something was moving around the stadium under this sheet. It would look as if some giant creature was running in circles. In reality no one moves around the stadium; each spectator simply stands up and sits back down in the same seat. There is energy moving around the stadium while the people remain stationary.

   Take a look at the physics definition again, with some help from our stadium model. In Physics a wave is defined as the lump traveling through a crowd by which energy is transferred from one member of the crowd to another without causing permanent seat changes within the crowd. Light moves in a similar motion as a crowd doing "the wave." Each particle of light is disturbed, but is not displaced.

Parts of the Wave

   The image below is a graphic representation of a wave. There are three key terms that are used to describe a wave and its motion. The images below represent two of them.

• Wavelength is the distance it takes a wave to make one full undulation. This distance is found between point A and point C and is represented by the horizontal black line in figure2. Wavelength of a light beam determines its color. The wavelength of visible light ranges from about 400 to 700 nanometers. Medical x-rays have even smaller wavelengths: about .1 nanometer. Television waves have the much longer wavelength of about one meter.
• Amplitude is the distance in which an undulation travels away from its horizontal axis, shown by the horizontal blue line. The amplitude is the vertical distance between point B and point C and is represented by the vertical black line. Amplitude measures the intensity of the light expressed by the wave.
• The third term, not represented in this image is frequency.Frequency describes the speed at which a wave oscillates. Measured in Hertz, frequency is measured by how many wavelengths, or full undulations, pass a designated point in a designated time, usually one second. Wavelength affects frequency because a wave with a longer wavelength will have to traverse a greater distance for one undulation to complete. If the wave has a small wavelength, many wavelengths can quickly pass the point. Though other waves such as sound vary in speed, light travels at a constant speed so its wavelength is inversely proportional to its frequency. Visible color can be decided by a wave's frequency because frequency and wavelength determine each other.

Electromagnetism

    Earlier it was stated that light is a form of electro magneticradiation. This term comes from a theory devised by James Clerk Maxwell, published in 1862. Maxwell discovered that there is a distinct relationship between electric fields and magnetic fields. He showed that when an changing, or oscillating, electric field was created ac hanging magnetic field formed around it, and when a changing magnetic field was created it formed an oscillating electric field around it. He called this relationship electromagnetism.

    From this discovery, Maxwell demonstrated electromagnetic radiation using an oscillating electric charge. This charge, as he predicted, created a region of oscillating electric and magnetic fields. These fields then created fields around themselves forming spheres of electromagnetic radiation. This radiation is considered to be among the four fundamental forces of nature and is the best understood of them. Maxwell published along with this finding a predicted velocity at which electromagnetic radiation travels. He said that this velocity was so close to that of light, "that is seems we have strong reason to believe that light itself is an electromagnetic disturbance." This force addresses the age old question: If a tree falls in the forest and nobody hears it does it make a sound? The tree creates a disturbance force because of its movement, but this disturbance is not sound until something, such as an ear, is around to interpret it. This same idea follows for light. Electromagnetic radiation travels freely, but unless the eye is interprets it the radiation is merely a wave and not what we know to be light.

Go Back to Light Rays

Move on to Reflection