The Electromagnetic Spectrum - Video Tutorials & Practice Problems
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The Electromagnetic Spectrum
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How's it going everyone? So in this video, I'm going to talk about the electromagnetic spectrum. This is something that you've probably seen before in other science classes, going all the way back to grade school. So I'm just gonna go ahead and fly right through it. Now, we know that electromagnetic waves just like all kinds of waves have wavelength and frequency. And if you sort of plot this out on a number line because there's no limit to how large and small those frequencies can get, you end up with a spectrum. And so this electromagnetic spectrum is what we call a continuum. This is just a number line that goes off to infinity in both directions. It's a continuum of electromagnetic waves otherwise known as light and it contains all possible wavelengths and frequencies. Now, different wavelengths and frequencies have very different properties in the universe. For example, visible light is like all the colors of the rainbow that you'd see, which is very different from an X ray that you would get at the doctor's office or something like that. So based on their properties, scientists have labeled certain portions or bands of the spectrum based on sort of like these ranges of wavelengths and these definitions are very arbitrary. In some textbooks, you might see different numbers. Basically, there's no really set rule or set number in which something becomes an X ray or something like that. All right. So I'm just gonna go ahead and sort of fly right through this. Um, you know, if you got your long radio waves on the left and your radio waves, this is where you would have your, your FM and AM stations like on a home or car radio or something like that. We've got microwaves like you would, you know, heat up your food in a microwave at home. We've got infrared radiation, which is otherwise known as thermal or heat radiation, whatever you feel heat, you're actually feeling an infrared electromagnetic wave. And then over here we've got this visible light portion and if you sort of blow it up, you see is you're going to see all the colors of the rainbow here. So all the colors of the universe that we see are actually just really in a narrow band of 350 nanometers along the electromagnetic spectrum. And that's all there is to it moving forward. We've also got ultraviolet rays. These are responsible for giving you sunburns on a really sunny day. We've got x rays that we talked about that you would get at the doctor's office. We've also got very powerful gamma rays that we see flying throughout the space in the universe. Um And we also use them to treat cancers and things like that. All right. So, uh there's actually a memory tool that we sort of come up here to help you sort of remember uh each of the names here and it's that large rude Martians invented very unusual X ray gadgets. So you can kind of just memorize that and each one of those letters here corresponds to the sort of band that it's uh it's talking the first letter, right. So um it's a memory tool that help you sort of like remember each of the bands. All right. Now, there's a couple of conceptual things that you'll need to know about the wavelengths frequencies and energy along the electromagnetic spectrum. So we can see here on the left side is on the left side, the wavelengths of these waves is very long and the wavelengths over here for gamma rays are very short. So we can say here is that on the left side, for long radio waves, you're going to have longer wavelengths. And then on the right side, you're going to have shorter wavelengths. Now, one of the things that we already know is that wavelength and frequency are inversely proportional. So in other words, lambda is inversely proportional to the frequency. So if you have a longer wavelength, then you're going to have a lower frequency because it's fewer cycles per second. And then that means that we're going to have a higher frequencies on the right side. Now, one of the things we're going to talk about a little bit later on, but I can tell you is that frequency is also related to energy. We're going to see that energy, the energy of lights is proportional to the frequency. So if you have lower frequency on the left, then you have lower energy and then you have higher energy on the right side, there was actually a really easy way to remember all of this information. One thing you can remember is that the LS um all are on the left side. So left side starts with L and that's where LS are so large radio waves have longer wavelengths, lower frequency and lower energy. And they're all on the left side. So everything with L is on the left side, all right. And then everything else is on the right side. All right. So the last thing I want to say here is that because um is that remember that all waves obey a mathematical relationship that the speed is equal to lambda times frequency. Now, light is a wave and light always moves at the same speed which we've talked about, which is the speed of light C. So that means we can actually just write our new equation which that C is equal to lambda times frequency. And to show you how this works, I'm actually gonna, we're just gonna jump in right into a problem over here. All right. So we have human beings continuously emit electromagnetic radiation or waves of approximately nine nanometers or sorry micrometers. So this is actually giving us a wavelength over here. Now, the first thing we want to do is we want to calculate the frequency of these electromagnetic waves. So that's going to be f well, we have this new relationship over here, this new equation. It's going to be pretty straightforward. We have C is equal to lambda times frequency. So that means that we can just move the frequency or sorry lambda over. So that means C over lambda is equal to frequency. So this is going to be three times 10 to the eighth meters per second and this is going to be divided by the wavelength over here. Now, remember that nine micrometers micro means times 10 to the minus six. So this is going to be nine times 10 to the minus six. All right. Now, I can go ahead and work this out. What you're gonna get uh is you're gonna get a frequency of 3.33 times 10 to the 13. Uh And that's gonna be whoops. And that's going to be in Hertz. All right. So that's your final answer. That's how you use. This equation is very straightforward. And we're going to move on to the next part here, which is which band of the electromagnetic spectrum do these waves belong to now, this is something we actually could have figured out already because we already have the wavelength. So we could have gone up there to the electromagnetic spectrum and find out where it sits. But now that we know the frequency, it's going to be a little bit easier. So this is what it calculated the frequency to be times 10 to the 13. And if you look at the frequency line, what you'll see is that 10 to the 14 is going to be pretty much squarely in the infrared. So this number here would actually sort of sit probably somewhere over here on the frequency spectrum. And so that means that these types of waves actually belong to the infrared radiation spectrum, infrared part of the electromagnetic spectrum. Anyway, folks, so that's your final answer. Let me know if you have any questions and I'll see you in the next video.
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Problem
Problem
A standard cell phone transmits electromagnetic waves with a frequency of 1.90×109Hz . Calculate the wavelength of these electromagnetic waves (in cm).
A
15.8 cm
B
5.70×1015cm
C
0.158 cm
D
0.0633 cm
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