13.1 EMR Types

Right, today we're gonna start our third unit, and our third unit, for the first chapters, is on electromagnetic radiation. Today, we're gonna figure out what it is and what the different types are. Just before we get going, the first thing to keep in mind here is that electromagnetic radiation is just a continuation of our last unit on electricity and magnetism. So, if we remember, Oersted was the first to figure out that if you have a moving charge or some sort of current going down a wire, it is able to produce a magnetic field. So, remember, if we have a current coming out of the page, we'd use our right-hand rule to figure out that the magnetic field then goes around it clockwise. Faraday, on the other hand, was the reverse. This is if we actually push a wire in a magnetic field, the resultant magnetic field is going inwards. He is the left-hand rule, then our thumb would point to the right, Rb is into the page, so our force goes downwards. So, we know that the current has to be going down the wire. So, those two guys were key in figuring out that electricity and magnetism were tied together. Electric charge moving creates a magnetic field, and a moving magnetic field will then produce a current. So, later, a guy named James Clerk Maxwell came along and tried to figure out how these two are connected. Basically, the key to his discovery is that an electric field will produce a magnetic field, and vice versa. The only trick is that the object has to be accelerating. So, in terms of acceleration, we need our speed to change. So, we have a VI - VF. Let's suppose we have some sort of acceleration that way, or it could just be direction. That's quite often what we do for regular electricity. So, in terms of current going up and down at our cell phone tower, suddenly it's just changing directions back and forth. So, that's what's creating our electric and magnetic fields. Because they're connected to each other, the idea is we're gonna keep them tied together, so we call it EMR, electromagnetic radiation. Radiation just means they're gonna go outwards from the source and then "allah eeehm" to combine the electricity and the magnetism. So, Maxwell came up with five key ideas, and they were later proven. He predicted that due to EMR, we'd get them anytime we have a charge in acceleration, which we did on the last page. Then, he said that whatever these charges vibrate at, so let's imagine an electron vibrating back and forth, whatever that frequency is, would also match the frequency of the EMR, which makes sense. He then [probably] another key one is that the speed of all the EMR travels at the speed of light. So, here's the sort of first two pictures, the speed of light being the source of EMR. So, light, x-rays, ultraviolet, all these different types are types of EMR. Maxwell first combined light with that idea. This third one is our fourth one is a key one. He says that the EMR travels perpendicular [to] each other. So, if we go back to this previous page, you can see in the bottom here, the red is sort of representing the electric field, so it's going up and down. The blue magnetic field is going in and out of the page, and you can see the wave is traveling to the right. So, if Maxwell said all of these things are perpendicular [to] each other, so the electric and magnetic have to be perpendicular and also perpendicular to the direction it's traveling. It's kind of like our third left-hand rule again. He said that anything that a transverse wave does. Everything that we've been doing in waves and physics 20, he says EMR will follow all of those same things, and we'll get to those over the next few days because electromagnetic radiation can be transferred or transfer of energy. That's what we're using to transfer energy. We got to think of anything that transfers energy typically as an EMR wave. So, in terms of using your remote control, that's EMR radiation. And even though visible light is what our most common one is because we can see it, there are all other types that have different frequencies, different wavelengths. But the key thing is, because Maxwell's at all everything travels up through to the eight, then they all have the same speed. And if we look at the spectrum, we're gonna go through from largest wavelength to the smallest wavelength or lowest frequency to the highest frequency. And we're gonna just see that visible light is a tiny portion of them. So, our EMR spectrum typically, we go from low to high frequency. That means that none of the wavelength is reverse going from large to small wavelengths. You can see here a wavelength radio waves are big, not the other end of the spectrum. Gamma radiation is quite small. And you can see the frequency works the opposite. So, for radio waves, our frequency is quite small, and gamma rays quite large. The other ones on this chart is really not that big of a deal but sometimes the size is a kind of a key idea to keep in mind. So, a radio wave is the size of like a huge building, microwaves the size of your height roughly, and then you can see it gets smaller and smaller as we go on. So, we'll quickly go through each of these. There are there is a spectrum below radio waves, and they're usually sort of manmade low-frequency kind of waves. We're not going to worry about them, typically start at radio as sort of being the first, and this is radio, radar, TV, any kind of signal, cell phone signal, anything like that, pretty low frequency, pretty safe radiation. And basically, how they're created is we just have the has electrons going up and down the tower so cell phone tower, your electrons just go up and down and they just vibrate back and forth, up and down the tower, and that's what creates the way that the receiving radio or cell phone or whatever picks up the signal. Next, we're gonna look at our microwaves, and it's kind of a bad meme because really they're not all that small, but they're smaller than radio waves, so I guess in that sense they're micro. But in terms of real-life objects, they're about the wavelength of your height, so like one to two meters, so they're quite large. And the reason why microwave ovens work the way they do is that frequency matches the natural resonance frequency. So, remember resonance means if you keep adding energy, it gets the wavelength and the energy gets bigger and bigger and bigger, and eventually, that'll excite the thing. So, in terms of a bridge collapsing or a wine glass shattering when it hits the right note, that type of thing. So, a microwave does sort of the same thing, it matches the resonant frequency of water, which excites the water, which basically causes it to boil, in essence, which then heats up your food. Okay, so kind of a poor name for it in terms of microwave, but they actually work pretty good, and they're relatively safe as long as you're not in a microwave oven. You're not going to get any kind of damage from microwaves. We actually use microwaves quite often to have better quality. So, if, like, a microwave is actually a better quality transmission than like an FM radio station or something like that back to radio. On the FM station, which is actually measured in megahertz, the frequency tells us how many frequencies per second the signal is going up and down the tower. For example, 100.3 megahertz is equivalent to 100.3 million Hertz. AM channels, on the other hand, have lower frequencies, such as 630 kilohertz, which is 630 thousand Hertz. AM typically has less frequency, which means it has a longer wavelength and can travel further. FM, on the other hand, has higher frequency, shorter wavelength, and usually clearer, better quality. This is why microwaves can be used for communication, as they provide even clearer signals, but they don't travel as far as FM. Moving along the spectrum, the next one is infrared. Infrared is basically heat energy, which we feel from sources like fire or heat lamps. We can use infrared goggles to detect different levels of heat, where hotter areas appear as red and cooler areas appear as yellowish. Infrared radiation is also utilized in devices like remote controls. Visible light is the spectrum that our eyes can perceive. It is the only part of the spectrum we can see, while other types of radiation are undetectable to us. The colors of visible light, in order of increasing frequency or decreasing wavelength, are red, orange, yellow, green, blue, indigo, and violet. The wavelengths of these colors vary, with red being approximately 700 nanometers and violet being around 352 nanometers. Next, beyond visible light, but still undetectable to human eyes, is ultraviolet (UV) radiation. UV radiation is the energy we receive from the sun, which can cause tans and sunburns. Sunscreens often indicate the level of UV protection they provide, with A being the safest, B being middle range, and C being the highest energy. It is important to protect ourselves from high-energy UVC rays to prevent sunburns and skin cancer. However, our bodies also need some UV radiation to produce vitamin D, so supplementation may be necessary in areas with limited sunlight. The last two types of radiation are the most dangerous. X-rays are an example of invisible radiation that is often used in medical imaging. They have high energy and can penetrate through soft tissues, providing detailed images of bones and organs. Finally, there are gamma rays, which are the most energetic and dangerous form of radiation. They are produced in nuclear reactions and can penetrate through the human body and other materials. Overall, understanding the different types of radiation and their properties is crucial in various fields, including communication, medical imaging, and safety precautions. X-rays have a pretty small wavelength, and they're so small that they can actually fit through the spaces of your skin, muscles, and tissues. That's why we use them for medicine, right? If we shine an x-ray on a person's hand, it'll pass through all of the flesh and muscles, but it won't get through bones and teeth. That's why we can see if a bone is broken or if your teeth are damaged when you go to the dentist. X-rays are okay at lower dosages, and if you only get them once in a while, but if you get them over and over again, it can cause damage and cancers. That's why your dentist leaves the room when they x-ray you, and that's why pilots have to take breaks more frequently to get out of the x-rays they experience in the atmosphere. Moving on, gamma rays are basically what we would think of as a nuclear bomb. They're the most dangerous, with super high energy and high frequency. However, they are also used for good purposes, such as killing cancer. People who undergo radiation therapy usually receive a mild dose of gamma rays to try to destroy the cancer cells. And if you watch The Avengers, it's gamma rays that make the Hulk! A couple of key things to remember about the spectrum: On one end, we have low frequency, and on the other end, we have high frequency, which typically coincides with energy. Radio waves have low energy and are pretty safe, while gamma radiation has high energy and is quite dangerous. That's a good way to remember it. As for infrared and ultraviolet, just remember that infrared is on the red end of the spectrum (ROYGBIV), and ultraviolet is on the violet end. Microwaves and x-rays come in between. You don't need to remember the numbers so much, just the order. That's it for today!