Measurement

Speed of Light

A fundamental physical constant that is the speed at which electromagnetic radiation propagates in a vacuum and that has a value fixed by international convention of 299,792,458 meters per second —symbol c. The distance light can travel in a unit of time through a given substance. Light travels through a vacuum at about 186,000 miles, or 300,000 kilometers, per second. ( See E = mc 2, electromagnetic waves, relativity, and twin paradox.)

Centimeter

A metric unit of length, equal to one hundredth of a meter.

Astronomical Unit

A.U. 93,000,000 miles. The distance from the earth to the sun.

Cycles

For cyclical processes, such as rotation, oscillations, or waves, frequency is defined as a number of cycles per unit time. In physics and engineering disciplines, such as optics, acoustics, and radio, frequency is usually denoted by a Latin letter f or by the Greek letter ν (nu). An interval of time during which a characteristic, often regularly repeated event or sequence of events occurs. A single complete execution of a periodically repeated phenomenon. A periodically repeated sequence of events.

Frequency

In physics, the number of crests of a wave that move past a given point in a given unit of time. The most common unit of frequency is the hertz (Hz), corresponding to one crest per second. The frequency of a wave can be calculated by dividing the speed of the wave by the wavelength.

Mega Hertz (MHz)

One million hertz, especially as a measure of the frequency of radio transmissions or the clock speed of a computer.

Meter

The fundamental unit of length in the metric system, equal to 100 centimeters or approximately 39.37 inches.

Hertz (Hz)

Unit of frequency equal to one cycle per second, 1928, named in reference to German physicist Heinrich Hertz (1857-1894).

Wavelength

Wave speed is the speed at which a wave travels. Wave speed is related to wavelength, frequency, and period by the equation wave speed = frequency x wavelength. The most commonly used wave speed is the speed of visible light, an electromagnetic wave.