TOEFL Listening: ETS-TOEFL听力机经 - SPV1825M8_XU3QW7Q$

Lecture: Electromagnetic Radiation: Narrator: Listen to part of a lecture in a physics class. Professor: Ok. Uh, we talked about different kinds of waves. Now let's go into a little more depth on one specific type of waves. Electromagnetic radiation, that's like the light, you see, out of the light bulb or from the Sun, or it could be like maybe X-rays or radio waves or microwave. Actually we're all different forms. Uh look at wavelength of the same thing, electromagnetic radiation. Male Student: Um, excuse me professor, but when you say electromagnetic is that like both electric and magnetic somehow? Professor: Well, yes. Any electromagnetic wave, like what we have with visible light or any of those other kinds of rays or wave we just mentioned. Any electromagnetic wave is made up of not only the record field, but also amazing magnetic field that produced right along with it. So usually, what we're concerned about, when we're talking about electromagnetic radiation, is it's electro, uh ... uh ... electric and magnetic field. Uh, when we say electric field, of course, we include anywhere nearby, where an electrically charged particles with the influence as this radiation passes by. And since it also has a magnetic field, we know that possibly look like nearby matter magnetically as well. Well, what we have to keep in mind here with the electric and the magnetic field? Well not always, uh, no, certainly not always. But at least in radiation of this kind, echo magnetic radiation, the field go hand in hand. You can't have one without the other. So I could talk about either one or both of them. In fact, though, your book and I will almost always choose to talk about the electric field only. Um, any idea why we'd rather talk about just the electric field most of the time? I mean based on our equations needed just as easily talking about a magnetic field and then figure out what the electric field is from that. But we don't usually. Any ideas why we generally want to zero in on the electric field right from the start? Female Student: Well, the electric field is probably a lot stronger, right? Professor: Well, I don't know who can actually say that any were different measured in different units. So it's kind of hard to compare them directly. But you're on the right track. It turns out that electricity interact with matter with the molecules and atoms that make up any material. That is, electric fields interact with matters. And generally this isn't true for every kind of matter, but generally they interact with matter a lot more strongly than magnetic fields do. So for example, when we see light bending, the light waves are electromagnetic, right? So when light is banned, like when it goes through the glass of a prism and comes out on all the difference rainbow colors, why does that happen? I mean, what causes that light, those electromagnetic waves, to bend in the first place? Well, no banned because of the interaction of electric field, the electrons and the atoms in the glass, the magnetic fields don't really do very much here in glass or in most other materials. And they just sort of along for the ride. So since It's easier in most materials to see the effects of the electric field. We normally like to look at that first and focus on that. That's why. That's the main reason we mostly talk about the electric field. It's easy to figure out the magnetic field later on, if you want to, uh, mathematically from the equation.