Everything Everywhere Daily: History, Science, Geography & More - The Electromagnetic Spectrum

Episode Date: October 11, 2022

All around you, right this second, you are surrounded by electromagnetic radiation.  You might better know this by names such as light, radio waves, microwaves, x-rays, or ultraviolet rays.  Fundamentally, they are all variations of the same phenomenon and are all part of the electromagnetic spectrum.  Learn more about the electromagnetic spectrum and how different wavelengths can behave very differently on this episode of Everything Everywhere Daily. Subscribe to the podcast!  https://link.chtbl.com/EverythingEverywhere?sid=ShowNotes -------------------------------- Executive Producer: Darcy Adams Associate Producers: Peter Bennett & Thor Thomsen   Become a supporter on Patreon: https://www.patreon.com/everythingeverywhere Update your podcast app at newpodcastapps.com Discord Server: https://discord.gg/UkRUJFh Instagram: https://www.instagram.com/everythingeverywhere/ Facebook Page: https://www.facebook.com/EverythingEverywhere Facebook Group: https://www.facebook.com/groups/everythingeverywheredaily Twitter: https://twitter.com/everywheretrip Website: https://everything-everywhere.com/everything-everywhere-daily-podcast/ Everything Everywhere is an Airwave Media podcast. Please contact [e-mail] to advertise on Everything Everywhere. Learn more about your ad choices. Visit megaphone.fm/adchoices

All around you right this second, you are surrounded by electromagnetic radiation. You might better know this by other names, such as light, radio waves, microwaves, x-rays, and ultraviolet rays. But fundamentally, they're all variations of the same phenomenon and are all part of the electromagnetic spectrum. Learn more about the electromagnetic spectrum and how different wavelengths can behave very differently on this episode of Everything Everywhere Daily. What if your perceptions about the past were wrong? ThruLine is a podcast that takes you back in time to uncover the parts of the story that may have gone unnoticed. It effectively turned day into night.

And how it shaped the world now. Time travel with us every week on the ThruLine podcast from NPR. As I mentioned in the introduction, electromagnetic radiation has many different names. Radio waves, microwaves, infrared and ultraviolet radiation, x-rays and gamma rays are all different manifestations of light. Visible light that we can see actually makes up a very small part of the total electromagnetic spectrum. So, for the purposes of this episode, if I refer to light, I'll actually be referring to any electromagnetic radiation. Electromagnetic radiation has properties that are similar to a particle, and they also have properties that are similar to a wave.

For the purpose of this episode, I'll mostly be speaking in terms of waves, but I will occasionally reference a photon. A photon is just a single unit or a quanta of energy that's emitted. The length of a wave, or the wavelength, defines the electromagnetic spectrum. If you can imagine a sine wave that goes up and down, the peaks in that wave will grow further apart if you stretch out the wave. They have a longer wavelength, the distance between the peaks of the wave. The wave will have a shorter wavelength if you compress the wave. The wavelength of light is inexorably tied up with the wave's frequency. The frequency is just the number of times that a wave goes up and down per second, and it's measured in a unit called Hertz.

A 2 megahertz radio signal, for example, will have a wave that goes up and down 2 million times per second. A 30 hertz wave will only go up and down 30 times per second. The relationship between frequency and wavelength is one of the simplest and most elegant equations in physics. Frequency times wavelength will always equal the speed of light. Also note that the longer the wavelength, the less energy a photon will have. Very short wavelengths like gamma rays contain an enormous amount of energy and can be very dangerous, and more on that in a bit. So the electromagnetic spectrum is just all of the different wavelengths of light.

And I should note that there is technically no theoretical maximum for a wavelength of light. There are practical limitations, however. A wavelength the size of the solar system would have a photon with so little energy that it would be near impossible to detect them from cosmic background radiation. There is, however, a minimum theoretical wavelength. It would be a light wave with a frequency known as the Planck frequency. It would be a two times 10 to the 43 hertz wave, and at that point each photon would become a black hole, which is far beyond what we need to worry about in this episode. So let's start our trip down the spectrum with what is known as extremely low-frequency radio waves,

or elf waves. Elf waves are between 3 and 30 hertz and have a wavelength of 100,000 to 10,000 kilometers. This is pretty much the limit of what humans can reasonably work with. The only real use for elf waves is communicating with submarines while they're in deep water. The United States used to run an elf transmitter in northern Wisconsin for this purpose. The antennas were just power lines that ran 14 miles or 23 kilometers in each direction of the transmitting station. The antennas were far smaller than the wavelength they work with, but you can get by using an antenna with a fractional wavelength. Just above this part of the spectrum are super low frequency waves. These are between 30 and 300 hertz and have a wavelength between 10,000 to 1,000 kilometers, and they're also

used for submarine communication. I should note that there are no hard and fast boundaries between the parts of the spectrum I'll be referring to. They're all arbitrary and can be divided or combined as is helpful. Next are ultra-low-frequency waves between 300 and 3,000-hertz, and have wavelengths from 1,000 to 100 kilometers. Again, this part of the spectrum isn't that useful, but it can penetrate the ground. There have been radio systems built for communicating with minds that have used this frequency. Next are very low-frequency waves, which are between 3,000 and 30,000-hertz, or 3 to 30-killerths. The wavelengths are between 100 to 10 kilometers. This is now starting to get into frequencies that have practical purposes.

Long wavelengths of radio waves can travel great distances, but have very low amounts of bandwidth available. The low-frequency spectrum is used for things like radio navigation and seldom for voice. From 30 to 300 kHz are low-frequency waves, with wavelengths from 10 to 1 kilometer. There are certain radio stations known as long-wave radio that use as part of the spectrum, and it's also used for aircraft navigation and other time signals. I have a clock above my computer, as I am recording this, that is synchronized to the atomic clock in Fort Collins, Colorado, that picks up a time signal at 60 kHz. For those of you who are geeky, the information sent to the clocks is sent at a rate of one bit per second. The complete time code is 60 bits, so it takes a minute to send a complete set of data.

From 300 kHz to 3 megahertz is the medium frequency part of the spectrum, which has wavelengths from 1 kilometer to 100 meters. This is the part of the spectrum where you'll find AM radio stations in the United States. In the U.S., AM radio is found between 540 kilohertz and 1.7 megahertz. In this range, you'll also find more navigation beacons as well as air traffic control radios. Above this, we find high-frequency radio. And I should note that the names are a bit odd because high-frequency is actually quite low, considering what's possible and what I'll be talking about. The high-frequency bands go from 3 to 30 megahertz and have wavelengths from 1.

100 to 10 meters. High-frequency radios have a special property, and that they can be reflected back to the earth by the ionosphere. This allows for radio waves that can travel very long distances, especially at night. And this is the realm of shortwave radio. Shortwave radio was heavily used during the Cold War to get radio signals into other countries. There are still shortwave radio stations that exist, and it can be fun to try to pick them up if you have the right receiver. Amateur radio or ham radio operators also use high-frequency radio to talk to people far away. Citizen band or CB radio can also be found in the 11 megahertz frequency range. Between 30 and 300 megahertz, we have very high frequency radio, or VHF, which has wavelengths from 10 to 1 meter.

VHF radio only works on line of sight, so it's only good for short distance communications. Amateur radio operators will use VHF radios, and VHF is also the primary part of the spectrum for terrestrial television. In the United States, FM radio stations also operate between 87.5 megahertz to 108 meghertz. Next is the ultra-high frequency or UHF radio. This has a range of 300 megahertz up to 3 gigahertz, with wavelengths of 1 meter down to 10 centimeters. UHF signals are used for a wide variety of things, including television, GPS, mobile phones, Wi-Fi, radar, and a host of other applications. The UHF part of the spectrum is subdivided into many smaller sections for specific purposes. Signals in this range can't travel very far and are also line of sight. However, they can carry much more information than lower frequency signals can.

The 2.4 gigahertz region became so popular because it wasn't actually assigned to anything. Because it was unlicensed, anyone could use it, and a whole host of applications found themselves there. Once you get to this part of the spectrum, because the waves don't travel as far, you don't have to worry as much about interference as you would with TV or radio stations. Above UHF, we have super-high frequency or SHF signals. They operate at 3 to 30 gigahertz and have wavelengths of 10 centimeters to 1 centimeter. This is the band where you'll find microwaves, which are great for narrowly focused point-to-point communications. You might have seen microwave antennas on radio towers that look like drums. You may have experienced some of this if you have

ever had to switch between 2.4 gigahertz Wi-Fi and 5-Gahertz Wi-Fi. The 5-Gahertz signal is probably faster and has more bandwidth, but it doesn't travel as well through walls. If you're ever in a hotel or maybe even parts of your own home, a 2.4-gaghertz signal might be better if you can't pick up a faster 5-gaghertz signal. Microwave ovens operate around 25 to 38 millimeters. Above this, we have extremely high frequency, or EHF signals. They have a frequent. of 30 to 300 gigahertz and wavelengths of 10 millimeters to 1 millimeter. We're now back into a part of the spectrum that isn't very useful. Waves in this region can be absorbed by the atmosphere, which don't make them useful for communications. At the very bottom of this range, there are

some 5G signals around 24 to 54 gigahertz, but the signals can only travel very short distances. Beyond that part of the range, signals can't be sent more than a meter before they're totally observed by the atmosphere. There are some applications here for scientific instruments and those millimeter wave security scanners that you walk through at the airport where you have to put your hands in the air. Above this, we start to enter the realm of infrared radiation. The definitions of the spectrum boundaries beyond this point become a bit messier, as there isn't the need to regulate this part of the spectrum.

I've actually come across several different ways to categorize the infrared spectrum, and I'll use one that's pretty broad. Far infrared radiation has a frequency of 300 gigahertz to 3 terahertz, with wavelengths of 1mm to 1 tenth of a millimeter. The biggest use of this part of the spectrum is in astronomy and infrared sensors, those that turn the lights on and off when you enter a room. Mid-infrared radiation is a frequency of 3 to 30 terahertz and a wavelength of 100 to 10 micrometers. And near-infrared radiation includes everything from about 30-terohertz up to 400-tera-hertz. infrared radiation is really important because it's basically heat. It's given off by planetary bodies and by your body.

The James Webb Space Telescope is tuned to view infrared light. An infrared light is the preferred light for use in many fiber optic cables because it travels the farthest in glass. Night vision goggles and cameras capture infrared light. As I said, the boundaries between these types of infrared radiation can be defined differently, but the upper boundary is very clear, because just above the infrared part of the spectrum is visible light. I'll probably do a future episode on this because there's a lot about the signs of colors,

rainbows, and prisms that are really interesting. The visible part of the spectrum extends from 400 terahertz for red, up to 790 terahertz for violet, and the wavelengths go from 625 to 400 nanometers. Just beyond the color of violet lies the next part of the spectrum, the ultraviolet, or UV. Ultraviolet has a wavelength of 400 nanometers to about 10 nanometers, and about 10% of the energy given off by the sun is UV radiation. Longer wave UV radiation can actually cause chemical reactions, and it's used by our bodies in the creation of vitamin D.

Shorter wave UV radiation, also known as extreme ultraviolet, can start to do damage to cells in DNA, and UV radiation is often used to sterilize medical instruments in water. Because we can't see UV radiation, if you've ever used a UV sterilizer, they'll often add a blue light to it just so you can see that it's working. Extreme ultraviolet is the beginning of what's known as ionizing radiation. As I mentioned before, the higher the frequency and the shorter the wavelength of light, the more energy an individual photon contains. And at this point and beyond, the photons have enough energy to do damage to biological organisms. After ultraviolet, we find x-rays. X-rays cover the range from 10 nanometers to 10 picometers, and have frequencies of 30 pentahertz to 30 X-a-hertz. X-rays were discovered by William Renkin in 1895 when images appeared on photographic film

when he stored him in a desk with a radioactive material. X-rays have so much power that they can go right through things, which is why they're used for imaging inside solid objects. Because it's considered to be ionizing radiation, exposure to x-rays has to be limited. If you've ever gotten an x-ray, you'll notice that the technician is almost always in another room when they activate it. Our last stop in the electromagnetic spectrum are gamma rays. Gamma rays are dangerous. They're one of the three types of radioactive decay from radioactive elements. Pretty much anything with a frequency over 30 x-hertz or a wavelength under 10 picometers is considered a gamma ray. Gamma rays have wavelength so small that you can't

build a mirror to reflect them, because the energy would just pass right through. And they're also extremely difficult to detect for the same reason. They have uses for certain sterilization procedures and aggressive cancer treatments. And there's a branch of astronomy that tries to observe gamma rays that are admitted by high-energy objects. They can also be produced in limited amounts by thunderstorms, and they also hit the Earth in the form of cosmic rays. So as you can see, even though all the different parts of the spectrum are waves of electromagnetic radiation, how they interact with the world and how useful they are is totally dependent upon their frequency and wavelength. The part of the spectrum, which is good for talking to submarines, isn't very good for Wi-Fi,

and visible light isn't very good for getting images inside your body. The really useful parts of the spectrum from low frequency through microwaves are all regulated through what is known as a spectrum plan. Different groups are given different parts of the spectrum for different purposes. However, these allocations can change over time. For example, taxi drivers used to regularly communicate via radio. However, you don't see as many taxi drivers using radios anymore. They just use cell phones, which are much cheaper and easier. The spectrum, which was allocated to taxis, was then able to be reallocated to something else. There are both national and international rules for how spectrum should be allocated, but that too is for another episode. All of us, in one way or another,

have used and interacted with different parts of the electromagnetic spectrum every day of our lives. understanding the different parts of the spectrum and what they can do is a worthwhile thing to know for everyone. Everything Everywhere Daily is an Airwave Media podcast. The executive producer is Darcy Adams. The associate producers are Thorntomson and Peter Bennett. I just wanted to extend a big thank you to everyone who is supporting the show over at patreon.com. I have show merchandise available there, including hoodies, t-shirts, and stickers. Plus, it really just helps me get this show out every single day, including, of course, weekends and holidays.

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