 Hi, I'm Relyne Professor Steven Neschivan, and I'm here to tell you a little bit about what is electromagnetic radiation. And for this little mini lecture, I'm just going to focus on the electric part, not the magnetic part of what's called electromagnetic radiation. And I'm really going to focus on what electromagnetic radiation does to charge particles, because that's kind of the key of it. And if we just imagine a ray of light, it's moving along at the speed of light, and maybe it happens upon a charged particle, could be the nucleus of an atom or maybe an electron, something like that. Well, as it happens, that light will cause those particles to accelerate up and down. And our interpretation of that is really where we get into what light is. And our interpretation goes something like this. This ray of light, we're going to think of as this thing that's propagating from left to right, still going at the speed of light. It's got this kind of waviness to it, among other things. We could say it has a certain wave line that goes from the peak of that to the peak of that there. So what is this? Well, what we're saying is that the light has a phase, the phase, in this case I've oriented to be right here in the plane of the board. And the idea is that when the positive phase of this light encounters a positive charge, it will accelerate that charge up. I haven't drawn it here, but you can imagine that when this whole wave of light gets a little bit farther forward and the negative phase of that light catches up with that positive particle, then it's going to actually have the opposite effect and it's going to accelerate it down. So you can see that the effect of electromagnetic radiation is this, you know, rapidly up and down acceleration of charged particles. Here's the thing, though. It has the opposite effect on negative particles. Namely, when the positive phase of the electromagnetic light is around a negative particle, it sends it down and instead of up. Now, of course, a little bit later, it's going to send it up. So it's also going to vibrate that. So I have a little diagram here for you. When the charge of the particle is positive and the phase of the particle, the phase of the light is positive, it accelerates up. I'm just going to do it that way, okay? And still having a positively charged particle, but the phase, this part here, when it catches up to the particle, it will do this, okay? And we have the opposite acceleration for a negatively charged particle. So I'm going to fill in that table that way. So what does this mean for what we have as an antenna? That's a whole, you can think of an antenna as being just a whole bunch of sort of fairly loosely held electrons on a wire. So as the light comes and hits that antenna, as long as when the positive phase of that light hits the antenna, it's going to send all those electrons down. How do I remember that? Well, because positive phase the antenna, negative charge sends the electrons down. But then a little bit later, when the negative part of the electromagnetic radiation catches up at that antenna, it will send it up, once again, according to that. So that's basically how radios work, is electromagnetic radiation moving electrons and antennas up and down. How does it work for atoms and molecules? Well, we kind of have a similar thing, but now the atom, the charges on the atom or molecule are pretty close together. So now we kind of have both effects at once. So for example, let's suppose the positive phase of the electromagnetic radiation is washing past this atom and this atom consists of a positive charge, maybe it's a hydrogen nucleus and an electron. Well, according to my diagram, when the positive phase is washing by that atom, it's going to send the positive part of the nucleus up and it will send the electron down. But then again, after a little while, when the negative phase catches up with this, it might reverse that effect. So you can imagine that it could sort of rock an atom or there might be other things that go on. Maybe the atom actually moves in a little bit in sync and we'll talk about that a little bit later. There's another possibility here. It's not separate atoms and a nucleon electrons, but we all know that the HF atom is pretty polar because fluorine is so electronegative. So it's kind of a similar thing when the positive phase of the light catches up with this molecule because of my little diagram here. It's going to send that fluorine down and it's going to send hydrogen up. But because they're stuck, it will tend to kind of rotate that molecule. OK, so that's that.