The wavelength of light is just the measure of the distance between two wave crests or two wave troughs. The units of measurement often vary depending on the wavelength region one is discussing. For example, radio waves have the longest wavelengths and scientists often use centimeters or even meters to describe their wavelength.

 

Visible light is often measured in units of nanometers (nm), one-millionth of a meter). Infrared light is commonly measured in microns, and x-rays are often measured in angstroms (one-ten millionth of a millimeter). To avoid having to know how big all these different units are it is convenient just to use fractions of a meter for all of them. But the fraction is so tiny – a billionth, or trillionth or much smaller – that scientific notation is used with a minus in front of the exponent. For example, a millionth of a meter is 10^-6, a trillionth is 10^-12 and a quadrillionth is 10^-15!

 

Frequency is the number of waves per second; very high frequency waves such as gamma rays vibrate up and down at the amazing rate of 10²⁰ times per second. A lot faster than humming bird wings flap (about 50 times per second)!  The unit to measure these vibrations is the hertz which is the unit for frequency: 1 Hz= 1 cycle/sec.

 

Visible Light

The part of the EMS that we are most familiar with is visible light. It is the only part of the EMS we can see, so it makes up our visual world. Here is a clever little widget that shows the exact color of any wavelength of visible light. To be a smart-alec, you could say you’d like to paint your room with paint at the wavelength of 517 nm. Nobody would understand you except a physicist and they don’t usually paint rooms.

 

 

The Greek letter lambda, λ, is the symbol for wavelength. The frequency, f, of a wave is defined as how many of the peaks pass a certain point in a given time. Since all radiation travels at the speed of light, c, we can then say:

 

 

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frequency = speed of light divided by wavelength f = c/λ

 

Sometimes the Greek symbol, “ν”, pronounced “new”, is used instead of “f”. So;

 

ν = c/λ

 

Now when someone asks you; What’s new?, you’ll know what to tell them!

 

Did you notice the important fact that frequency and wavelength are reciprocals of each other? If you know one you can use Eqn 6.1 to convert it to the other.