Using a fundamental property of the universe to study the universe
We interact with electromagnetic waves (also known as electromagnetic radiation) on a daily basis. It is simply a form of energy that we use to heat food, listen to music in the car, see the world around us, solve crime, treat cancer, and so much more. To fully understand the physics of electromagnetic radiation would require a 4 year degree, and arguably more. This article, however, will help you understand just how important this stuff is, and how fundamental understanding allows us to make sense of the world around us.
Electromagnetic Waves Defined
An Electromagnetic (EM) Wave (or radiation) is a technical term for light, however it also encompasses many other things such as X-rays, Microwaves, and Radio Waves. Let’s break down the term. Electro- means electric, or referring to electrons. -Magnetic referring to magnets or the magnetic properties of the matter. Lastly, wave, describing the shape or structure of the matter. Light, as in the stuff you see and interact with and all the colors in their full glory, is in fact an electromagnetic wave that is composed of two components, a magnetic and an electric component. These components are technically fields that oscillate in magnitude.
You can visualize this as two waves with the same wavelength, frequency, and intensity that act in different planes. The electric portion of the wave exists vertically while the magnetic component exists in a horizontal plane, as seen below.
Organizing Electromagnetic Radiation
X-rays, Ultraviolet light, Visible light, Microwaves, Radio Waves, and all of the other types of electromagnetic radiation are organized by their frequency, which is a continuous variable that allows us to classify the matter into categories, ranging from highest frequency to lowest frequency. That classification is called the electromagnetic spectrum.
Wavelength, another property of electromagnetic radiation, can also be used to categorize the energy as well. Wavelength is inversely proportional to frequency. This means that as frequency increases, wavelength decreases, and vice versa. Therefore the electromagnetic spectrum also ranges from smallest wavelength to largest wavelength.
Energy and Frequency
We have these waves, say visible light waves, and they all have their associated energies as defined by E= hv. Here, E stands for energy, h represents Planck’s Constant, and v is frequency. We can easily understand the relationship between frequency and energy by simplifying the equation.
If we assume the h is equal to 1 (which it isn’t, it’s actually about 6.62610-34) then we can see the relationship between frequency and energy. If you observe an electromagnetic wave with a frequency of 2 units (units are arbitrary in this example, but the answer is Hertz for the overachievers), then your equation would look like E=1*2, where h=1 and v=2. In this case E=2. however, if you were to increase frequency, you could see that E would also increase. Therefore, when we organize electromagnetic energy by frequency, we are also organizing it by the amount of associated energy, from greatest to smallest.
How Is This Useful?
We have a use for just about every single type of electromagnetic radiation that exists on the spectrum. Let’s take a look at some examples.
For the scope of this article, you can assume that Gamma rays are the most energetic form of electromagnetic radiation, with a frequency of roughly >1020 Hz. We use this in medicine to preform what is called Gamma Knife Surgery. Gamma Knife Surgery falls under the category of Radiosurgery, which isn’t surgery in the sense of incisions, scalpels, and sutures, but rather a procedure that involves using high energy radiation to treat cancers and abnormalities.
You have likely experienced this radiation before, if you have ever needed to be evaluated for an injury or fracture of a bone. We use X-Rays to look at bone because their energy is great enough to pass through our soft tissues but not our bone. Therefore, we can capture the X-ray images, we can get a stunningly accurate depiction of the human skeleton. Frequency ranges roughly between 1018 and 1020 Hz.
Ultraviolet light (UV light) is just below the visual light spectrum. This is the light that you can thank for sunburn you may receive in the summer time. Also known as a Black Light, UV light is also popular for initiating fluorescence. We use of UV light has allowed great advancements in the field of forensic science. Frequency ranges roughly between 1016 and 1018 Hz.
This is, obviously, the light that we can see. The human eyes have adapted to sense the differences in wavelength of light entering the pupil in order to determine color. The color that we see is actually the color or wavelength of light that does not get absorbed by the object. Grass is green because it absorbs all wavelengths of light except green. White light, like when you glance at the sun, is a mixture of all colors. Frequencies for the visible light spectrum (the small subset of the electromagnetic spectrum in which the colors are arranged by frequency as well) range from roughly 1013 to 1016 Hz.
Infrared Light is just above the visible light spectrum, and is used commonly in electric heaters, short-range communications, fibre-optic communication, as well as thermal imaging cameras. The heat that your body releases is in the form of infrared radiation, therefore we can use it to “visualize” heat. Frequency ranges between 1012 and 1013 Hz.
The irony in “Microwave” is that they are actually far from “micro” in terms of size. Microwaves, as in the appliance, use microwaves, as in the radiation, to excite water molecules in food in order to heat it up. Microwaves are now a common kitchen appliance. Frequency ranges between 108 and 1012 Hz.
Lastly, radio waves, as you guessed it, are used communicate music and audio over a long distance. This has been common for quite some time, and is still widely used today. Frequency ranges between 104 and 108 Hz.
Using this knowledge, we can see planets that are lightyears away. Just recently, we have for the first time, imaged a Black Hole. We did this by not only capturing visible light, but as much electromagnetic radiation as possible from the direction of the black hole. The appearance, although not impressive to the average bear, was an enormous achievement for both the physical and astronomical community. The amount of data accumulated to produce that image was somewhere in the ballpark of 4.5 petabytes. In common terms, the equivalent of taking 4,000 phone pictures a day for the past 200 years. We can thank the understanding of electromagnetic radiation for this achievement.