|Themes > Science > Astronomy > Modern Astronomy > Properties of Light > Wave Properties of Light|
Light as a WaveThe quantity that is "waving" is the electromagnetic field, an esoteric but quite measurable entity: your lights shine and your microwave runs and your radio plays because the electromagnetic field exists. As illustrated in the adjacent image, a wave has a wavelength associated with it.
It is normal to give the wavelength of light the symbol Greek "lambda". Some common units of length employed for wavelengths of electromagnetic radiation are summarized in the following table. (The micrometer is often still called by its old name, the micron.)
The speed of light in a vacuum is commonly
given the symbol c. It is a universal constant that has the value
The speed of light in a medium is generally
less than this. Normally the term "speed of light", without further qualification,
refers to the speed in a vacuum.
where c is the speed of light and h is another universal constant called Planck's Constant that has the values
in two different useful sets of units (eV stands for "electron volts"; electron volts and ergs are two common units of energy). Thus, these equations allow us to freely interconvert among frequency, wavelength, and energy for electromagnetic waves: specifying one also specifies the others.