# How exactly are high energy EM waves harmful for us?

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## Main Question or Discussion Point

I've always read in my Physics textbooks that high energy EM waves like x-rays and gamma rays, if our body is exposed to them for a long time, can damage the skin significantly. However, how does that happen at an atomic level?

As far as I'm concerned, the thing that differentiates a high energy wave (HEW) from a low energy wave is that the HEW has a greater frequency and because of that, more radiation is absorbed by our body in a smaller time, resulting in damage. Is it so?

## Answers and Replies

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Higher energy waves can more easily ionize (or even fully dissociate) the atoms in molecules in our bodies. When these get ionized, they are no longer the molecules that they are supposed to be. That would be one basic-level description.

Frequency is proportional to energy. Don't confuse wave frequency and particle rate ("intensity", sometimes).

Higher energy waves can more easily ionize (or even fully dissociate) the atoms in molecules in our bodies. When these get ionized, they are no longer the molecules that they are supposed to be.
So what exactly do high energy waves have which allows them to do so? At an atomic level, how do these waves differ from a low energy waves, like radio waves?

The lower frequency (energy) waves, like radio waves, don't have the energy to knock out electrons from the atoms (ionize the atoms). If the field has enough energy, they can rip an electron off of that atom. This is an action that could change the physical or chemical nature of a molecule in your body.

This is really a quantum effect, so it is difficult to explain in terms of physical construction of a wave. Suffice it to say that its all about energy. If you have studied atomic energy levels, then low energy waves might not have the energy required to excite an electron to the n=infinity level of its orbital, thereby releasing it as a free particle.

The lower frequency (energy) waves, like radio waves, don't have the energy to knock out electrons from the atoms (ionize the atoms). If the field has enough energy, they can rip an electron off of that atom. This is an action that could change the physical or chemical nature of a molecule in your body.
So, for a high school graduate, you can't really paint a picture about what happens at an atomic level? Though, if I imagine a zigzag line for a wave, then maybe I can see that more the zigzag there will be, more the chances of the wave hitting an atom and then knocking off an electron. But I suppose even if radio waves hit us, they can't knock off an electron because of their low energy, so the zigzag picture is invalid (or so, I think).

Also, the take out from this post is that high frequency waves have more energy as compared to low frequency waves because the two are directly proportional.

Drakkith
Staff Emeritus
Science Advisor
So, for a high school graduate, you can't really paint a picture about what happens at an atomic level? Though, if I imagine a zigzag line for a wave, then maybe I can see that more the zigzag there will be, more the chances of the wave hitting an atom and then knocking off an electron. But I suppose even if radio waves hit us, they can't knock off an electron because of their low energy, so the zigzag picture is invalid (or so, I think).
Indeed, the zig-zag picture is not correct here. Put simply, EM waves interact with matter in a discrete manner, not a continuous manner. Instead of a smooth oscillation as the fields alternate back and forth, the energy from the EM wave is delivered in "bursts", "chunks", or "packets" that are called photons. The higher the energy of the incoming EM wave, the higher the energy of each photon. It is the sudden absorption of energy by an atom or molecule from a sufficiently high frequency EM wave that ends up ionizing it. In order to ionize most biological molecules the frequency of the EM wave needs to be in the UV range or higher.

When you add together the sum effect of a huge number of low-energy photons interacting with a material you get the classical picture. For example, antennas are usually described by classical EM theory, not by Quantum Electrodynamics, since it works perfectly well for that purpose and you can't really observe the individual photons of EM waves in the microwave region of the spectrum and below. The energy of each photon is simply too low. But if you add together the energy of ten-trillion photons, then you can view their collective behavior as a classical EM wave.

Indeed, the zig-zag picture is not correct here. Put simply, EM waves interact with matter in a discrete manner, not a continuous manner. Instead of a smooth oscillation as the fields alternate back and forth, the energy from the EM wave is delivered in "bursts", "chunks", or "packets" that are called photons. The higher the energy of the incoming EM wave, the higher the energy of each photon. It is the sudden absorption of energy by an atom or molecule from a sufficiently high frequency EM wave that ends up ionizing it. In order to ionize most biological molecules the frequency of the EM wave needs to be in the UV range or higher.

When you add together the sum effect of a huge number of low-energy photons interacting with a material you get the classical picture. For example, antennas are usually described by classical EM theory, not by Quantum Electrodynamics, since it works perfectly well for that purpose and you can't really observe the individual photons of EM waves in the microwave region of the spectrum and below. The energy of each photon is simply too low. But if you add together the energy of ten-trillion photons, then you can view their collective behavior as a classical EM wave.
Ok, so I understand the picture of radiation by assuming that light is composed of photons. But there's also a theory that said that light behaves as waves, correct? What happened to that?

Drakkith
Staff Emeritus
Science Advisor
Ok, so I understand the picture of radiation by assuming that light is composed of photons. But there's also a theory that said that light behaves as waves, correct? What happened to that?
Nothing happened to it. That is Quantum Electrodynamics, the same theory that states that light acts as a particle.*

From wiki's article on wave-particle duality: Wave–particle duality is the concept that every elementary particle or quantic entity may be partly described in terms not only of particles, but also of waves. It expresses the inability of the classical concepts "particle" or "wave" to fully describe the behavior of quantum-scale objects.

As the quote states, some aspects of light require it be described as a wave, yet other aspects require that it be described as a particle.

*Kind of. The truth is much more complicated and nuanced.

sophiecentaur
Science Advisor
Gold Member
Ok, so I understand the picture of radiation by assuming that light is composed of photons. But there's also a theory that said that light behaves as waves, correct? What happened to that?
OMG. Don't get us started on that one.
All EM radiation is basically all the same stuff. The only difference is in the frequency. Light and the rest can either be 'explained' in terms of waves or in terms of Quanta (Photons). The term "particle" to describe photons is very confusing because the word Particle is not the same as when used in macroscopic terms like grains of sand, bullets, dust. I just wish that a different terms had been coined when photons were originally identified.
The easiest way to calculate, describe or predict what happens to light on the way from A to B is to treat it as a wave. When it interacts with matter (emitted by a hot wire or registering on your retina) it does so in fixed quanta of energy and those quanta behave like particles during that very short period of interaction.
So it's not a matter of either / or. It's a matter of 'and'. Modern Physics is just not straightforward, I'm afraid. The term "Wave/particle duality" was popular in the recent past. Google it, if you want some light bed time reading. But be prepared for some rubbish in amongst the good stuff.
[Edit: Hot dang! Drakkith said all this already.]

OMG. Don't get us started on that one.
:D :D Then I guess I'll keep the photons and energy picture in my head and be in a bliss till I learn the complicated stuff.

sophiecentaur
Science Advisor
Gold Member
:D :D Then I guess I'll keep the photons and energy picture in my head and be in a bliss till I learn the complicated stuff.
There's plenty of stuff available to read on the subject of the Duality. Browse through a few sites. Reputable ones with .gov extensions can usually be relied on and there's always the dreaded Physics Forums; try a search here.

I'd recommend not diving too deeply into the duality topic in your analysis of this particular question. You'll get that info when you need it in your education. For now, just believe that there are discrete photons which carry the energy of your EM wave, and these are the individual things that can collide with and modify your body (or whatever they hit).

Fervent Freyja
Gold Member
Well, I'm still alive after years of laying down in a box that continuously radiates very hot UVA/UVB rays around my entire body for 20 minutes at a time. The most threatening burns I have gotten has always resulted from spending a long day in the sun with unprepared (untanned) skin.

sophiecentaur
Science Advisor
Gold Member
Alive but 'undamaged'?
I have just had a Rodent Ulcer (basal cell carcinoma) removed from my temple. Caused by exposure to the Sun. (Poor man's equivalent to your box). Malignant Melanoma, otoh, is a nastier alternative.