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We call that radiant energy. So that light being emitted, that's the reason why we can see this fire. Radiant energy. Now you might say, okay, maybe that's all of the energy in the system, but I'll say, no, there's another form of energy, and actually, even in this picture, that's probably where most of the energy is, ... | Introduction to energy Energy and enzymes Biology Khan Academy.mp3 |
Now you might say, okay, maybe that's all of the energy in the system, but I'll say, no, there's another form of energy, and actually, even in this picture, that's probably where most of the energy is, and that's potential energy. So where is the potential energy? Well, it's sitting in the bonds of the fuel over here. ... | Introduction to energy Energy and enzymes Biology Khan Academy.mp3 |
So these are either chips of wood or charcoal of some kind, but these are formed by carbon-carbon bonds. So you have these carbon-carbon bonds, and they can be bonded to other carbons or other things, and they're also going to be bound to some hydrogens here and there. So you're going to have bonds like this that actua... | Introduction to energy Energy and enzymes Biology Khan Academy.mp3 |
They have the potential to be released. If you're able to break these bonds, those electrons are going to get into a lower energy state, or they might bond with other things, and in the process, they're going to release energy that's going to be radiant energy and thermal-slash-kinetic energy. So how does this happen? ... | Introduction to energy Energy and enzymes Biology Khan Academy.mp3 |
How do these bonds actually get broken? Well, that's our good old friend, the combustion reaction. That's our good old friend, the combustion reaction, where you take some oxygen, you take some heat, or we could say some energy. So it takes a little energy to get started. That's why you might have to light this with a ... | Introduction to energy Energy and enzymes Biology Khan Academy.mp3 |
So it takes a little energy to get started. That's why you might have to light this with a match to begin with. So oxygen plus energy, and then you could say, plus these carbon-carbon bonds, you could say plus whatever it is, these fuels which are made out of carbon, either charcoal or wood. So plus, I'll do it like th... | Introduction to energy Energy and enzymes Biology Khan Academy.mp3 |
So plus, I'll do it like this, I'll draw some carbon-carbon bond right over here. That's going to combust. I'll do this in a color. So that is going to, I'm really having trouble changing colors. This is going to combust, and it's going to release water because the fuel has hydrogens in it. It's going to release carbon... | Introduction to energy Energy and enzymes Biology Khan Academy.mp3 |
So that is going to, I'm really having trouble changing colors. This is going to combust, and it's going to release water because the fuel has hydrogens in it. It's going to release carbon dioxide, and it's going to release a lot more energy. I'll do that in caps. It's going to release a lot more energy, and that energ... | Introduction to energy Energy and enzymes Biology Khan Academy.mp3 |
I'll do that in caps. It's going to release a lot more energy, and that energy we see in the form of the kinetic energy of the molecules and the radiant energy being emitted. Now you might say, okay, I can buy that. I have this potential energy here, and this potential energy that's in the bonds between these atoms, we... | Introduction to energy Energy and enzymes Biology Khan Academy.mp3 |
I have this potential energy here, and this potential energy that's in the bonds between these atoms, we call that chemical potential. So we have chemical potential energy. Potential energy is right over there. But you might say, okay, I buy that. The chemical energy is being converted into the thermal energy and the r... | Introduction to energy Energy and enzymes Biology Khan Academy.mp3 |
But you might say, okay, I buy that. The chemical energy is being converted into the thermal energy and the radiant energy. This is actually an interesting point. This is the law of conservation of energy. Energy cannot be created or destroyed. It can only be converted from one form or another. But you might be saying,... | Introduction to energy Energy and enzymes Biology Khan Academy.mp3 |
This is the law of conservation of energy. Energy cannot be created or destroyed. It can only be converted from one form or another. But you might be saying, okay, I can convert from one form to another, but how can this actually do work in the way that I've even depicted here? Well, the entire Industrial Revolution is... | Introduction to energy Energy and enzymes Biology Khan Academy.mp3 |
But you might be saying, okay, I can convert from one form to another, but how can this actually do work in the way that I've even depicted here? Well, the entire Industrial Revolution is all about trying to convert from one form of energy to another and also to do work. So a steam engine is fundamentally based upon co... | Introduction to energy Energy and enzymes Biology Khan Academy.mp3 |
Combustion is what's going on in your car engines where the pistons are expanding due to the thermal energy, and that helps drive the drivetrain of the actual car. So it can clearly do work. So here we have some other examples. This is lightning. And so when you see the lightning, there's something clearly very kinetic... | Introduction to energy Energy and enzymes Biology Khan Academy.mp3 |
This is lightning. And so when you see the lightning, there's something clearly very kinetic is going on. You have electrons moving from the cloud to the ground. And you might say, so this right over here, you could say that's kinetic energy. And you might say, well, how can I do work with that? Well, that's what the w... | Introduction to energy Energy and enzymes Biology Khan Academy.mp3 |
And you might say, so this right over here, you could say that's kinetic energy. And you might say, well, how can I do work with that? Well, that's what the whole electronics industry is all about. That's what power lines are all about, movement of electrons. That's current, and current can be used to do all sorts of a... | Introduction to energy Energy and enzymes Biology Khan Academy.mp3 |
That's what power lines are all about, movement of electrons. That's current, and current can be used to do all sorts of amazing things. You can actually have an electric motor as one way to actually do it. So that's kinetic energy there. There's clearly radiant energy going on. We can see the lightning, and that radia... | Introduction to energy Energy and enzymes Biology Khan Academy.mp3 |
So that's kinetic energy there. There's clearly radiant energy going on. We can see the lightning, and that radiant energy is due because the air gets ionized and gets heated, and so there's also thermal energy. As the electrons go down, there's heat that is actually being generated. Now, where did this energy come fro... | Introduction to energy Energy and enzymes Biology Khan Academy.mp3 |
As the electrons go down, there's heat that is actually being generated. Now, where did this energy come from? It just doesn't come from anywhere. Well, you have all this potential energy that starts building up in these clouds as the water vapor rises, and the mechanism isn't fully understood of how this happens, but ... | Introduction to energy Energy and enzymes Biology Khan Academy.mp3 |
Well, you have all this potential energy that starts building up in these clouds as the water vapor rises, and the mechanism isn't fully understood of how this happens, but because of energy from the sun, you have water vapor rising. As the water vapor rises through the clouds, the bottom part of the cloud becomes more... | Introduction to energy Energy and enzymes Biology Khan Academy.mp3 |
And so you have these electrons that really want to get down here, and then the ground, because the air above the ground becomes more negative, the ground starts becoming more positive. And so you can imagine these electrons more and more want to get down here, but this air isn't a natural conductor. But once the elect... | Introduction to energy Energy and enzymes Biology Khan Academy.mp3 |
The air essentially gets ionized, and the electrons are able to find a path. So while this is all building up, you have this electrostatic potential building. So this is electrostatic, static, you can't see that that well, electrostatic potential. And how this forms, once again, it's an area that people are still, ther... | Introduction to energy Energy and enzymes Biology Khan Academy.mp3 |
And how this forms, once again, it's an area that people are still, there's some good theories out there about how this forms, but it's not 100% well established. And over here in this third old drawing of this person doing a handstand dive, this is probably the most typical example of potential energy being converted ... | Introduction to energy Energy and enzymes Biology Khan Academy.mp3 |
And over here it's very clear he has the potential to fall, and it has the potential to turn it into kinetic energy. And so once he falls over, at this point, most of his potential energy has been converted into kinetic energy. So here it's potential, and here it is kinetic energy. So the big takeaway is energy, it's t... | Introduction to energy Energy and enzymes Biology Khan Academy.mp3 |
So the big takeaway is energy, it's the ability to do work, it cannot be created or destroyed, but it can be converted from one form to another. And all of the forms, at their essence, you can really think about them in two big buckets. You can think about them as potential energy or kinetic energy. And as a last examp... | Introduction to energy Energy and enzymes Biology Khan Academy.mp3 |
And light is, at least to me, it is mysterious. Because on one level, it really defines our reality. It's maybe the most defining characteristic of our reality. Everything we see, how we perceive reality, is based on light bouncing off of objects, or bending around objects, or diffracting around objects, and then being... | Introduction to light Electronic structure of atoms Chemistry Khan Academy.mp3 |
Everything we see, how we perceive reality, is based on light bouncing off of objects, or bending around objects, or diffracting around objects, and then being sensed by our eyes, and then sending signals into our brain that create models of the world we see around us. So it really is almost the defining characteristic... | Introduction to light Electronic structure of atoms Chemistry Khan Academy.mp3 |
And probably the most amazing thing about light, well, actually there's tons of amazing things about light, but one of the mysterious things is when you really get down to it, and this is actually not just true of light, this is actually true of almost anything once you get onto a small enough quantum mechanical level,... | Introduction to light Electronic structure of atoms Chemistry Khan Academy.mp3 |
I'm not used to things behaving as both. And it really depends on what experiment you run and how you observe the light. So when you observe it as a particle, and this comes out of Einstein's work with the photoelectric effect, and I won't go into the details here, maybe in a future video when we start thinking about q... | Introduction to light Electronic structure of atoms Chemistry Khan Academy.mp3 |
We call these particles photons. If you view light in other ways, and you see it even when you see light being refracted by a prism here, it looks like it is a wave. And it has the properties of a wave. It has a frequency, and it has a wavelength. And like other waves, the velocity of that wave is the frequency times i... | Introduction to light Electronic structure of atoms Chemistry Khan Academy.mp3 |
It has a frequency, and it has a wavelength. And like other waves, the velocity of that wave is the frequency times its wavelength. Now, even if you ignore this particle aspect of light, if you just look at the wave aspect of light, it's still fascinating, because most waves require a medium to travel through. So for e... | Introduction to light Electronic structure of atoms Chemistry Khan Academy.mp3 |
So for example, if I think about how sound travels through air, so let me draw a bunch of air particles. I'll draw a sound wave traveling through the air particles. What happens in a sound wave is you compress some of the air particles, and those compress the ones next to them, and so you have points in the air that ha... | Introduction to light Electronic structure of atoms Chemistry Khan Academy.mp3 |
And you can plot that. So we have high pressure over here, high pressure, low pressure, high pressure, low pressure. And as these things bump into each other, and this wave essentially travels to the right, and if you were to plot that, you would see this waveform traveling to the right. But this is all predicated, or ... | Introduction to light Electronic structure of atoms Chemistry Khan Academy.mp3 |
But this is all predicated, or this is all based on, this energy traveling through a medium. And I'm used to visualizing waves in that way. But light needs no medium. Light will actually travel fastest through nothing, through a vacuum. And it will travel at an unimaginably fast speed, 3 times 10 to the 8th meters per ... | Introduction to light Electronic structure of atoms Chemistry Khan Academy.mp3 |
Light will actually travel fastest through nothing, through a vacuum. And it will travel at an unimaginably fast speed, 3 times 10 to the 8th meters per second. And just to give you a sense of this, this is 300 million meters per second. Or another way of thinking about it is it would take light less than a seventh of ... | Introduction to light Electronic structure of atoms Chemistry Khan Academy.mp3 |
Or another way of thinking about it is it would take light less than a seventh of a second to travel around the Earth, or it would travel around the Earth more than seven times in one second. So unimaginably fast. And not only is this just a super fast rate, or a super fast speed, but once again, it tells us that light... | Introduction to light Electronic structure of atoms Chemistry Khan Academy.mp3 |
Because it's not just an unimaginable fast speed, it is the fastest speed not just known to physics, but possible in physics. So once again, something very unintuitive to us in our everyday realm. We always imagine that, okay, if something is going at some speed, maybe if there was an ant riding on top of that somethin... | Introduction to light Electronic structure of atoms Chemistry Khan Academy.mp3 |
But nothing can go faster than the speed of light. It's absolutely impossible based on our current understanding of physics. So it's not just a fast speed, it is the fastest speed. It is the fastest speed possible. And this right here is an approximation. It's actually 2.99 something something times 10 to the 8th meter... | Introduction to light Electronic structure of atoms Chemistry Khan Academy.mp3 |
It is the fastest speed possible. And this right here is an approximation. It's actually 2.99 something something times 10 to the 8th meters per second. 3 times 10 to the 8th meters per second is a pretty good approximation. Now, within the visible light spectrum, and I'll talk about what's beyond the visible light spe... | Introduction to light Electronic structure of atoms Chemistry Khan Academy.mp3 |
3 times 10 to the 8th meters per second is a pretty good approximation. Now, within the visible light spectrum, and I'll talk about what's beyond the visible light spectrum in a second, you're probably familiar with the colors, maybe you imagine them as the colors of the rainbow. And rainbows really happen because the ... | Introduction to light Electronic structure of atoms Chemistry Khan Academy.mp3 |
And you can see that in maybe a clearer way when you see light being refracted by a prism right over here. And the different wavelengths of light, so white light contains all of the visible wavelengths, but the different wavelengths get refracted differently by a prism. So in this case, the higher frequency wavelengths... | Introduction to light Electronic structure of atoms Chemistry Khan Academy.mp3 |
And if you want to look at the wavelength of light, they're a visible light, it's between 400 nanometers and 700 nanometers, and the higher the frequency, the higher the energy of that light. And that actually goes into when you start talking about the quantum mechanics of it. That the higher frequency means that each ... | Introduction to light Electronic structure of atoms Chemistry Khan Academy.mp3 |
They have a better ability to give kinetic energy to knock off electrons or whatever else they need to do. So higher frequency, let me write that down. Higher frequency means higher energy. Now, I keep referring to this idea of the visible light. And you might say, what is beyond visible light? And what you'll find is ... | Introduction to light Electronic structure of atoms Chemistry Khan Academy.mp3 |
Now, I keep referring to this idea of the visible light. And you might say, what is beyond visible light? And what you'll find is that light is just part of a much broader phenomenon, and it's just the part that we happen to observe. And if we want to broaden the discussion a little bit, light is just, or I should say ... | Introduction to light Electronic structure of atoms Chemistry Khan Academy.mp3 |
And if we want to broaden the discussion a little bit, light is just, or I should say visible light, is just really part of the electromagnetic spectrum. So light is really just electromagnetic radiation. And everything that I told you about light just now, it has a wave property, and it has particle properties. This i... | Introduction to light Electronic structure of atoms Chemistry Khan Academy.mp3 |
This is not just specific to visible light. This is true of all of electromagnetic radiation. So at very low frequencies or very long wavelengths, we're talking about things like radio waves, the things that allow a radio to reach your car, the things that allow your cell phone to communicate with cell towers. Microwav... | Introduction to light Electronic structure of atoms Chemistry Khan Academy.mp3 |
Microwaves, the things that start vibrating water molecules in your food so that they heat up. Infrared, which is what our body releases, and that's why you can detect people through walls with infrared cameras. Visible light, ultraviolet light, the UV light coming from the sun that will give you sunburn. X-rays, the r... | Introduction to light Electronic structure of atoms Chemistry Khan Academy.mp3 |
X-rays, the radiation that allows us to see through the soft material and just visualize the bones. Gamma rays, the super high energy that comes from quasars and other certain types of physical phenomena. These are all examples of the exact same thing. We just happen to perceive certain frequencies of this as visible l... | Introduction to light Electronic structure of atoms Chemistry Khan Academy.mp3 |
We just happen to perceive certain frequencies of this as visible light. You might say, hey Sal, how come we only perceive certain frequencies of this? How come we only see these frequencies? Literally, we can see those frequencies with our unaided eye. The reason, or at least my best guess of the reason of that, is th... | Introduction to light Electronic structure of atoms Chemistry Khan Academy.mp3 |
Literally, we can see those frequencies with our unaided eye. The reason, or at least my best guess of the reason of that, is that's the frequency where the sun dumps out a lot of electromagnetic radiation. It's inundating the earth, and if as a species you wanted to observe things based on reflected energy, a reflecte... | Introduction to light Electronic structure of atoms Chemistry Khan Academy.mp3 |
It is possible that in other realities or other planets, there are species that perceive more in the ultraviolet range or in the infrared range, and even on earth there are some that perform better at either end of the range. But we see really well in the part of the spectrum where the sun just happens to dump a lot of... | Introduction to light Electronic structure of atoms Chemistry Khan Academy.mp3 |
I think that's a pretty good overview of light. If any of this stuff seems kind of unintuitive or daunting or really on some level confusing, this wave-particle duality, this idea of a transfer of energy through nothing, and it seems unintuitive, don't worry. It seems unintuitive even for the best of physicists. You're... | Introduction to light Electronic structure of atoms Chemistry Khan Academy.mp3 |
You're already at the leading edge of physics thinking. | Introduction to light Electronic structure of atoms Chemistry Khan Academy.mp3 |
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