Glossary of Terms

LIGHT

Light is the propagation of energy in the form of electric and magnetic waves and is therefore also known as electromagnetic radiation. The electromagnetic spectrum is the entire range of possible kinds of electromagnetic radiation, which are classified by the frequency of the wave. The spectrum ranges from gamma rays, which have a very short wavelength and very high energy, to radio waves, which have a very long wavelength and very low energy. Visible light makes up a very small portion of the spectrum, as is illustrated in figure 1.

The Electromagnetic Spectrum

The Electromagnetic Spectrum

Visible light itself can be divided into smaller groups, also based on different wavelengths which our brains interpret as colors. White light is a mixture of all of the different colors in the visible spectrum. When passed through a prism, white light can be broken into individual bands of colored light, like a rainbow as in figure 2. You may have noticed this effect when you see a rainbow across the water from your lawn sprinklers. In this instance, each individual drop in the mist of water from the sprinklers is acting as a prism.

Figure 2 - A prism separating white light into the visible spectrum

Figure 2 - A prism separating white light into the visible spectrum

ATOMS AND ELEMENTS

We humans have suspected the existence atoms for philosophical reasons for much longer than we have had the capability of observing them. Although the atom was originally conceived of as the smallest unit of matter possible, we now know that a single atom is made up of a nucleus surrounded by a cloud of electrons.

The nucleus of an atom is made up of protons, which have a positive electrical charge and (usually) neutrons, which have a neutral electrical charge. The orbiting electrons have a negative charge. A typical atom in a “normal” state has the same number of electrons as protons, and hence a net charge that is neutral

Depiction of a helium atom.  Note that one femtometer (fm) is equal to 1 X 10^–15 meters.

Depiction of a helium atom. Note that one Angstrom is equal to 10^-10 meters and one femtometer (fm) is equal to 1 X 10^–15 meters.

While the atom is not the smallest unit of matter, it can still be considered to be the smallest unit of matter that still maintains it’s chemical properties. Atoms of different chemical elements are distinguished from each other by the number of protons and electrons. For instance, a hydrogen atom has one proton and one electron, while helium has two protons and two electrons and iron has twenty-six protons and twenty-six electrons.

The Periodic Table of the Elements.  Each element is numbered according to its number of both protons and electrons

The Periodic Table of the Elements. Each element is numbered according to its number of both protons and electrons

One Response to “Glossary of Terms”


  1. […] of the basic tenets of quantum physics is that an atom of any chemical element is only capable of particular levels of kinetic energy unique to that element. It is important to […]


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