Properties of Light

Light is a unique thing. We can think of it terms of both waves and particles called photons. In this post, we are going to look at only the wave nature of light, or in general, all electromagnetic radiation of which light is only a small subset.


 


Electromagnetic radiation is made up of both electric fields and magnetic fields which propagate perpendicular to each other. The wave itself, moves in the third direction, perpendicular to the fields.

where B is the strength of the magnetic field, E is the strength of the electric field, and c is the speed of light (3x10⁸ m/s)

 

So what exactly is a wave? Waves have maxima (crests), minima (troughs), and zero points (nodes).

We can also take a measure of a wave by looking at the distance between successive crests (or troughs) which we call the wavelength, represented by the Greek letter lambda (λ). This can be measured in meters, nanometers (10^-9 m), or Ångstroms (10^-10 m symbolized by Å).

Or we can look at a point in space and how long it takes two successive crests (or troughs) to pass that point in space. This is called the frequency, symbolized as either f or ν (Greek letter nu). This value can be measured in the inverse of seconds (1/s) or Hertz.

The cool thing about the wavelength and the frequency is that you can multiply them together to get the speed of the wave. In our case, for light, the speed is just c.

c= λ*ν

 

Lastly, when we are talking about visible light, we are talking about all light that can be seen by the human eye. They range in color from red to violet (ROY G. BIV), with the longer wavelengths and shorter frequencies closer to the red end of the spectrum and the shorter wavelengths with higher frequencies near the violet end.

For visible light, red is approximately 7000 Å and 430 terahertz (10¹² Hertz). Violet is around 3000 Å and 1 petahertz (10¹⁵ Hertz). 

These will become important later on.