What is Light and How is it Produced
All matter has an internal property of energy. This energy is related to the electrons traveling in orbits around the nucleus of the atoms. As the electrons change orbital levels, energy is emitted or absorbed. For example, if we burn a sheet of paper, energy is given off, which we see as a flame. The matter in the filament of a light bulb emits light when it is excited by an electrical current.
The term that we use for emitting energy from matter is called radiation. Radiation is often referred to as electromagnetic radiation because the emitting energy has both electrical and magnetic properties.
The emitted energy is transmitted at a wavelength determined by the nature of the matter and the forces acting on it. The human eye can only detect a very small range of wavelengths of radiation. What it detects we call light. Physicists often refer to it as visible light.
The electromagnetic spectrum, shown in Figure 12.1, includes the energy emitted at all wavelengths. This includes radio waves, microwaves, infrared rays, visible light, ultraviolet rays, X-rays, gamma rays, and other electromagnetic radiation of longer and shorter wavelengths.
Radio waves, which we use for AM, FM, TV, and shortwave radio, range in length from around 1 centimeter to a kilometer long. Some naturally occurring radio waves are much longer, actually thousands of kilometers long.
At the opposite end of the spectrum are the gamma rays, which are radioactive and have a wavelength of less than a trillionth of a centimeter.
Note that the names given to various portions of the spectrum are arbitrary labels chosen by scientists for convenience. By setting up these artificial divisions, scientists can describe the specific nature of the waves they are examining. The various portions of the spectrum blend into one another. For example, a microwave and a radio wave at their point of contact would be identical (Chen, Kao, & Liu, 1999).
Electromagnetic radiation has three properties: wavelength, amplitude, and polarization. Wavelength is the length of the wave, which determines its properties. In visible light the wavelength determines the color. The amplitude of a wave determines the brightness of the light. Polarization is the angle at which the wave is vibrating.
For us to appreciate the nature of polarization of light, we need to think in three dimensions rather than two dimensions as on a piece of paper. When we show waves on a sheet of paper, the wave is shown moving up and down. In reality, it can move at any angle from the paper. A polarized light filter such as that used on sunglasses or photographic cameras is designed to filter out the waves that are not parallel to the filter plane. This can reduce the glare off a body of water or other glaring objects. When two polarized filters are placed in front of one another, and one of the filters is rotated, that is, when the two filters become 90° apart, all of the light is filtered out and no light can pass through.
Light’s Enigma: The Duality of Wave and Particle Theories of Light
Scientist have long debated whether light is a wave of energy or a particle of matter. That light demonstrates characteristics of both light and matter is accepted by most physicists. The particle characteristic of light is that particles called photons travel at the speed of light. Light is the only wave that can travel though a vacuum.
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