LIGHT AND MATTER: WHAT THEY ARE

Light: What is Is and Its Behavior

Light is a wave-train of electric and magnetic energy. Similar to a train with many cars, and each car has a size, light is a long train of packets of electric and magnetic energy (called a photon). The length of these packets, which we call the wavelength, defines the characteristics of the light. In light with long wavelengths, the electric energy is not compressed and oscillates less rapidly and so we say that light carries low energy. In light with short wavelengths, the electric energy is very compressed and oscillates much more rapidly, and we say the light carries high energy.

The behavior of light allows it to be spread out into a spectrum. A given light beam comprises many photons and each of these photons can have a unique and different wavelength. When the light passes through a medium change (i.e from air to glass), different wavelengths respond differently, and light is bent. We use a prism or a grating to bend the different wavelengths (or colors) at different angles and in this way we create a spectrum. Blue light bends more sharply (deflects it direction or motion) more than red light. The resulting rainbow of segregated light is a spectrum (water droplets in the air act like tiny prisms and result in the beautiful rainbows you see in the sky).

The Electromagnetic Spectrum

There is a large electromagnetic spectrum in which different light carries different energy. We seen only a small visible region with our eyes.

There are names for the different regions of the electromagnetic spectrum. High energy light has high oscillation frequency and short wavelengths. Low energy light has low oscillation frequency and long wavelengths.

In order of high energy light to low energy light:

Gamma-rays, X-rays, ultraviolet, visible, infrared, microwave, radio

The wavelength of visible light ranges from 400 nm to 700 nm, where a "nm" is a nanometer, or 1 billionth of a meter. Radio waves can have wavelengths as long as a football field and even as large as the distance across the United States! The wavelengths of Gamma-rays and X-rays are smaller than single atoms and carry so much energy, that they can be harmful to your body (break up your DNA molecular bonds) when the penetrate you.

Matter: Elementary Particles

Atoms are composed of three types of elementary particles:

• protons (positive electric charge)
• neutrons (no electric charge, about same mass as proton)
• electrons (negative electric charge, about 1/1000 mass of protons and neutrons)

Atomic Structure

The protons and neutrons form a nucleus, tightly bound together at the center of the atom (like the sun in the center of the solar system). The electrons "orbit" around the nucleus.

Atoms are mostly empty space. If the nucleus was expanded to the size of a grape seed, the electron would orbit with a distance of a 1/4 of a mile!

Each element is defined by the number of protons in the nucleus. This number is called the atomic number. Some of the same elements have different numbers of neutrons in their nucleus; the same elements with different neutrons are called isotopes.