Light energy can travel through space as electromagnetic radiation in the form of either particles or waves. Now in a vacuum of space, light moves at a speed of 3.00×108 meters per second. This is known as the speed of light. Now when it comes to quantum mechanics and talking about frequency and wavelength, there are these dual ideas that light is just a collection of tiny particles moving together, whereas others say no, light moves as a wave, a unified wave through space. Just realize that both of these help to give us a complete picture of what electromagnetic radiation is and how light energy is involved. Now in terms of the wave part of this idea, the top of the wave is known as the crest and the bottom is called the trough. So here, the top of this wave, so here, here, and here, these are our crests. And then the bottom parts here and here, these are our troughs.

Now, when we talk about wavelength and frequency, wavelength uses the Greek symbol lambda, which looks like this: λ. Wavelength is just the distance from one crest or trough of a wave to the next one. It is expressed in units of meters. So we're talking about 1 crest to another crest or 1 trough to another trough. The distance between them, that is our wavelength, which is lambda. Frequency uses the Greek symbol of mu, which kinda looks like a curvy v. It is the number of waves you have per second. So if we look here, we'd say that this is 1, 2, and then 3 waves. So there's 3 waves involved here. Okay? This scenario describes the total number of waves, the frequency, which is mu. μ. Now when it comes to mu, it is expressed in units of seconds inverse or Hertz. Okay? So seconds inverse is the same thing as Hertz. So just remember, when we're looking at a wave of light energy, we have wavelengths and we have frequency involved.