Ch.6: Waves and Electromagnetic Radiation

wave

A traveling disturbance that carries energy from one place to another without requiring matter to travel across the intervening distance.

wavelength

The distance between adjacent wave crests, the highest points of adjacent waves.

x rays

High-frequency and high-energy electromagnetic waves that range in wavelength from 100 nanometers to 0.1 nanometer, used in medicine and industry.

ultraviolet radiation

High-frequency wavelengths, shorter than visible light, ranging from 400 nanometers to 100 nanometers.

visible light

Electromagnetic waves with a wavelength that can be interpreted by nerve receptors in the brain; wave- lengths range from 700 nanometers for red light to 400 nanometers for violet light.

speed of light

The velocity at which all electromagnetic waves travel, regardless of their wavelength or frequency; equal to 300,000 kilometers per second (about 186,000 miles per second).

transmission

One of three responses of an electromagnetic wave encountering matter, in which light energy passes through the matter unaffected. See also absorption and scattering.

refraction

A response of an electromagnetic wave to matter, in which the wave slows down and alters direction. See also absorption and transmission.

reflection

A process by which light waves are scattered at the same angle as the original wave; for example, from the sur- face of a mirror.

radio wave

Part of the electromagnetic spectrum that ranges from the longest waves—wavelengths longer than Earth's diameter—to waves a few meters long.

microwaves

Electromagnetic waves, with wavelengths ranging from approximately 1 meter to 1 millimeter, which are used extensively for line-of-sight communications and cooking.

interference

When waves from two different sources come together at a single point, they interfere with each other. The observed wave amplitude is the sum of the amplitudes of the interfering waves.

light

A form of electromagnetic wave to which the human eye is sensitive. Light travels at a constant speed and needs no medium for transfer.

hertz

The unit of measurement for the frequency of waves; one wave cycle per second.

frequency

The number of wave crests that go by a given point every second. A wave completing one cycle (sending one crest by a point every second) has a frequency of one hertz,

1 Hz.

electromagnetic spectrum

The entire array of waves, vary- ing in frequency and wavelength, but all resulting from an accelerating electrical charge; includes radio waves, micro- waves, infrared, visible light, ultraviolet, X-rays, gamma rays, and others.

electromagnetic wave

A form of radiant energy that reacts with matter by being transmitted, absorbed, or scattered. A self-propagating wave made up of electric and magnetic fields fluctuating together. A wave created when electrical charges accelerate, but requiring no medium for transfer. Electromagnetic radiation.

Doppler effect

The change in frequency or wavelength of a wave detected by an observer because the source of the wave is moving.

absorption

One of three possible responses of an electromag-

netic wave encountering matter, in which light energy is converted into some other form, usually heat energy. See also transmission.

diffuse scattering

A process by which light waves are absorbed and reemitted in all directions by a medium such as clouds or snow.

infrared radiation

Wavelengths of electromagnetic radiation that extend from a millimeter to a micron; felt as heat radiation.

gamma ray

The highest-energy wave of the electromagnetic spectrum with wavelengths less than the size of an atom, less than one-trillionth of a meter; normally emitted in very high-energy nuclear particle reactions.