Stack Overflow for Teams — Collaborate and share knowledge with a private group. Create a free Team What is Teams? Learn more. If visible light has more energy than microwaves, why isn't visible light dangerous? Ask Question. Asked 2 years, 10 months ago. Active 2 years, 2 months ago. Viewed 34k times. Improve this question. Add a comment. Active Oldest Votes. Improve this answer. Thomas Blankenhorn Thomas Blankenhorn 1, 2 2 gold badges 4 4 silver badges 8 8 bronze badges.
So, according to that definition of "energy", a microwave source does have substantially less energy than a visible light source, regardless of how much power either source puts out. Smith G. Smith The same amount of energy from visible light does far more damage. But adding it to the answer is probably a good idea, since it seems suse doesn't understand that part.
Show 12 more comments. Dmitry Grigoryev Dmitry Grigoryev 4, 1 1 gold badge 14 14 silver badges 32 32 bronze badges. Just at very low levels. A standard microwave oven puts W of electromagnetic energy into whatever you put inside it many ovens actually do more these days.
A wifi router is limited to 4 watts EIRP of RF radiation, which falls off with distance on the familiar inverse-square law.
Irradiance probably is the more relevant measure for this question, but is harder to describe in layman's terms. Using raw power as a proxy gets the point across to within an order of magnitude. Show 4 more comments. Show 2 more comments.
This is expressed in two ways: Proteins in the epidermis outer skin layer are more resistant to heat than those in the deeper skin layers There are more nerve endings in the outer layers of skin, so dangerous heating by visible light causes more pain, urging you to escape the dangerous situation Oh, and the most obvious difference: visible light is visible. That is roughly equal to the intensity of natural sunlight. I believe staring at the Sun will make you blind much faster.
Schneider Sure - emphasis on outside the body. Inside the body is a very different story. That's because our skin has been very well adapted to protect us. Now there's a sweet spot where all the radiation is absorbed in the body, and it penetrates some distance - which is how cancer treatment works; however attempting to suggest that masters in physics is related to the media is insulting, and I'd be thankful if you could refrain.
A 2kW theatrical followspot with an IR-reducing coating so probably W in cm diameter has a beam powerful enough that you wouldn't leave your hand in it for long or choose to put it back in.
No, the main difference between visible light a microwaves as in microwave-oven is the power. Of course, visible light will roast your skin before the heat penetrates deeper by conduction. But because its damage is confined to the skin, a much shorter exposure to W visible light will do lasting damage than W microwaves. Show 11 more comments. I'm aware of the case of pacemakers, but how would this work in the fully natural situation?
If it's not resonance you're talking about, then what is it? So, a black chicken will cook well in strong visible light, but a white chicken will require higher power, because it reflects more.
Microwaves work well because they penetrate deeper before they get absorbed due to longer wavelength , but also absorb WELL because the frequency is tuned near the resonance for water molecules. So, if you tuned your light specifically to a transition that breaks some specific bonds, or heat just specific tissues.
This can do more damage because it may change chemistry, but luckily, breaking bonds requires quite high frequencies - see next case below. With MW and IR, you will still end up just heating the sample if you find a resonance resonances in MW, IR and visible are mostly vibrational and rotational transitions, not bond changing, except for red-colored substances reacting to visible light, which you notice when red dyes bleach quickly in intense light.
Phil Frost Phil Frost 3, 3 3 gold badges 22 22 silver badges 26 26 bronze badges. So even with something as supremely deadly as antimatter, the dose makes the toxin. Golding M. Golding 39 1 1 bronze badge. There is a danger mainly because you don't realize you're too close to the light and there's no eye response to the increasing amount of light hitting your eyes , and if it's dark, your pupils are maximally dilated.
You don't see microwaves, but above about 20 W, the heat is quite noticeable, and a W light is unmistakably warm those are usually used for heating, though, not IR camera illumination. Reed Shilts Reed Shilts 2 2 bronze badges. Anonymous Anonymous 39 1 1 bronze badge. See explanation e. Not to mention that you can heat up butter just fine in a microwave.
When you put butter in a hot pan, the bubbles are the water boiling off. I think the more correct phrasing is that most microwave ovens emit at a frequency that corresponds to a peak in the absorption spectrum of water.
This answer is right in noting that absorption is another key factor in addition to the energy per photon and the intensity of light. The point is that the photons reflected from the other side of the microwave oven will not be lost they're in phase with the photons coming from the magnetron. This has nothing to do with water, just with using energy efficiently. Indeed, if you use two magnetrons in a microwave oven, perfectly out of phase, pretty much all the food heating effect is lost you do get some , since the food item disrupts the "perfection" of the cavity, but it's only a fraction of the power draw of the magnetrons.
Show 6 more comments. Gamma ray photons from radioactivity are even worse, but they are fortunately rare. Stig Hemmer Stig Hemmer 3 3 silver badges 5 5 bronze badges. Featured on Meta. Now live: A fully responsive profile. Linked Related 0. Hot Network Questions. Question feed. Physics Stack Exchange works best with JavaScript enabled. Accept all cookies Customize settings.
The internal energy of the molecules increases when they absorb microwaves, which causes heating. Microwaves pass easily through the atmosphere, so they can pass between stations on Earth and satellites in orbit. Infrared light is used by electrical heaters, cookers for cooking food, and by infrared cameras which detect people in the dark. Infrared light has frequencies which are absorbed by some chemical bonds.
The internal energy of the bonds increases when they absorb infrared light, which causes heating. This makes infrared light useful for electrical heaters and for cooking food. All objects emit infrared light. The human eye cannot see this light but infrared cameras can detect it. This 'thermal imaging' is useful for detecting people in the dark. Visible light is the light we can see. I think you would call it "ionization" as the process of going from gas to plasma involves ionizing the atoms or, in other words, separating electrons from the atomic nuclei.
Microwaves do have a longer wavelength than visible light and that does mean that they have a lower energy. Microwaves are able to pop the popcorn by disrupting the rotational motion of the water stored in the popcorn kernel. By disrupting this motion, the water starts to move around faster and eventually pressure build will pop the kernel.
I also believe that microwave light is more intense than visible light. By this I mean that if you were to increase the intensity of visible light, such as having a certain amount of visible light brought down to a point source like a LASER, than you would be able to pop the popcorn.
You are absolutely right about the relationship between wavelength and energy. If you want to heat something up by bombarding it with radiation, then ultraviolet light will work better than visible light, and you'll be sitting around forever waiting for your popcorn if you use infrared light or radio waves.
This kind of heating works just by increasing the velocity of the molecules in the object. Luckily for the shareholders of General Electric, there's more to it than that. What you have to know is that different wavelengths of light have different effects on individual molecules. UV light has enough energy to break chemical bonds, which is why you get skin cancer -- UV from the sun breaks bonds in the DNA of skin cells. Visible light can't break bonds, but it can knock electrons up to a higher orbital state -- chlorophyll, retinal, and other pigments work by changing their shape in response to this kind of electron movement.
Microwave radiation is too weak to do any of those things, but what it can do is cause polar molecules to isolate. You probably know that water is a dipole because one side of the molecule has non-bonded electrons orbiting the oxygen atom and is therefore slightly negative , and the other side has the two hydrogen atoms that are somewhat positive because the electrons 'shared' between the O and H atoms spend more time orbiting the large O nucleus which has lots of protons than the small H nuclei which have only one proton.
If you put this dipole in a magnetic field it would orient itself along the magnetic field, just like a small magnet moves if you hold it near a large magnet.
If you put a dipole in an oscillating magnetic field of the right frequency, the dipole will oscillate, too. Well, waves of electromagnetic radiation have that name because they're made of an oscillating electric wave and an oscillating magnetic wave. And it happens that the microwave radiation we use in microwave ovens has a magnetic component with precisely the right frequency to cause water dipoles to oscillate.
So you put a glass of water in the microwave oven, and the microwaves start flowing. The microwaves cause the water molecules to start oscillating, and this oscillation heats up the glass of water. The microwaves don't make molecules move around and heat up like UV radiation would, but it does cause molecular motion by making the water dipoles oscillate. As a result, microwaves only heat up things with water in them, so you can't heat up a brick in a microwave.
Your kid sister's Easy-Bake oven with a strong lightbulb in it will heat up the brick, but it's going to take a lot longer to boil a glass of water! As for your second question, I don't know of a name for that phase change.
A quick look on the internet seems to indicate that there isn't a name for plasma-related phase changes. On the one hand this makes sense, because things don't change back and forth from plasma very often, so we don't really need a name for that. On the other hand, scientists love naming things, and we have plenty of fancy names that are perfectly useless, so it's sort of surprising that nobody has invented a name for plasma phase changes.
So if you want a fun project, you should just invent a name for a gas-plasma phase change.
0コメント