# Tag Info

130

Your question contains a premise that is false: Microwaves do not have less energy than visible light per se. They only have less energy per photon, as per the Planck–Einstein relation, $E = hf$. In other words, you can raise the power of electromagnetic radiation to a dangerous level at any wavelength, if only you generate enough photons – as your microwave ...

112

We do use (near) infrared radiation to heat food – whenever we toast food or grill (UK)/broil (US) by beaming infrared downwards on to food! The point is that the infrared is strongly absorbed by the food we cook in this way, and doesn't penetrate significantly beyond about a millimetre. So the surface of the food is strongly heated – seared, toasted or ...

84

The very first thing you should do is stop using your oven and have it checked out by an authorized repair service. If in fact the oven was operating with the door open, there was a failure of the door interlocks to turn the oven off and a failure of the backup system intended to permanently shut the oven off in the event the interlocks failed which, ...

62

It is because cheese has a nice combination of water and fat. The water is important since the microwave transfers energy to it by making the water molecules vibrate. On the other hand, oils, in general, have lower specific heat (compared to water). This means that given the same amount of heat, the temperature change is higher for fat than for water. You ...

59

I get the same thing reheating some discs of glazed carrots. And there are several videos of folks doing this intentionally with grapes. An article published last year in PNAS says this will happen with almost any pair of similarly-sized object with sufficient water. The shape of the pairs appears to set up a resonance that concentrates the electric field ...

49

If you stare at the Sun you’ll go blind. And if you spend a lot of time in the sun, you’re likely to get skin cancers. So visible light seems plenty dangerous to me. Some of the damage may actually be from infrared and ultraviolet light, but these are close in frequency to visible light and very far from microwaves. By the way, the intensity also matters, ...

44

The magnetron injects microwave radiation at a certain rate. Ignoring losses, that radiation bounces around the walls until it’s absorbed by the food. If you put two burritos in there instead of one, on average there will be fewer bounces before absorption. That means that with two burritos, the average intensity of the radiation impinging on any point is ...

42

It's more like the walls were semi-transparent glass, if you want to imagine it as light (and even then, you neglect diffraction effects). It would actually be better to imagine it as sound! But this seems to be exactly what you're looking for: http://arstechnica.com/gadgets/2014/08/mapping-wi-fi-dead-zones-with-physics-and-gifs/

42

The dose (or, in this case, the intensity) makes the poison. You're constantly exposed to microwaves since that's what 99% of wireless communication devices use, and you're also constantly exposed to visible light unless you sleep in an isolation tank. Both can be dangerous if you increase the intensity sufficiently.

41

Popcorn pops in a microwave oven due to the microwaves interacting with the moisture in the popcorn kernel raising its internal temperature and pressure. Once the pressure increases enough the kernel pops and the moisture escapes and cools. The moisture in the un popped kernel remains hot. Hope this helps.

33

Microwave heating is largely caused by the changing electric and magnetic fields (i.e. the "microwaves") which are emitted by your microwave oven affecting polar molecules. As the direction of the electric field changes over time, the polar molecules (often, of water) attempt to follow the field by changing their orientation inside the material to line up ...

31

How hot (or cold) something feels is not just down to temperature, but to the rate of heat transfer, or thermal conductivity. Popped corn is a good insulator, having a foam-like structure. As a result, little heat escapes to the hand. Unpopped corn is a much better conductor of heat, and transfers heat to the hand much more quickly, so that it feels much ...

30

Visible light is dangerous if you have the same power output as a microwave in a confined space There are several factors to consider here. One is that, per photon visible light has more energy than microwave radiation. But this is misleading: a microwave oven puts about 1 kW of power into a confined space. That's a lot of power. You don't often see that ...

27

We do. That iron on the top of the device is a simple ohmic resistor, which gets the 230V network current directly. There is no need for any converter or stabilization of the temperature or the electricity, because increased resistivity of the iron due to the temperature and the second law of the thermodynamics safely keeps the iron to around 700K, while ...

25

In microwave ovens what matters is how much energy the radiation carries and how that energy is absorbed by the food. Visible light and IR are rapidly absorbed by most foods, so they would only heat the outer layer of the food. You'd get food with the outside carbonised and the inside raw. Microwaves are far less strongly absorbed by foods, so they ...

24

Different molecules and different crystalline structures have frequency dependent absorption/reflection/transmission properties. In general, light in the human visible range can travel with little absorption through glass, but not through brick. UV can travel well through plastic, but not through silicate-based glass. Radio waves can travel through brick ...

22

This Isn't About Water Microwave heating actually has nothing to do with the moisture content of items. It has everything to do with the amount of electric dipoles (polar molecules) in the item of concern. Water molecules (with many other organic molecules) happen to be electric dipoles. (That is, one side of the molecule has a positive charge and the other ...

22

Assuming the intensity is the same, microwaves are more dangerous than visible light because they penetrate the skin to a greater depth (1-2 cm; more info is in Wikipedia). Humans have more adaptation to visible light than to microwave radiation, because they were exposed to light for millions of years. This is expressed in two ways: Proteins in the ...

22

As already pointed out, microwaves in the oven have just the right frequency to heat water molecules. But this alone does not explain why chocolate with a tiny bit of milk heats up so much quicker than a glass of milk. The key is heat capacity. With no milk the chocolate is almost transparent to the microwaves. Even a little bit of milk makes the mixture ...

22

When reading your post, it seemed to me that the most likely explanation for your experience is that the microwave did turn off, but the ventilation did not. You may have mistaken this for the microwave not turning off. If indeed the microwave didn't turn off, you would have felt pain and other sensations immediately. Get a new microwave in that case, and ...

22

This makes me think that the heat introduced to the substance should be directly proportional to the polarity of the molecule. In addition to the good answer from Gert, there's a problem in this step. The microwave oven is a metal box. The purpose of the metal box is to reflect whatever microwaves aren't absorbed by the food (either because they "...

21

It's hard to access how 'accurate' an analogy is (i.e. how is this being quantified?). But, I think, there is a simple - better analogy: WiFi is more like sound in a house. The transmitter is a speaker. If its a good, loud speaker, you will still easily be able to hear it in the next room - through a wall. A few walls inbetween and it gets very faint. ...

20

The danger of electromagnetic waves is a function of the photon energy, the intensity of the source and your distance from it, and the qualitative nature of the interaction of a specific frequency with organic matter. That latter bit is very complex. The visible spectrum, down to about infra-red, doesn't penetrate the top layer of skin, or most clothing, ...

20

@Ben Crowell answer is correct 👍. The following is only intended to expand upon his points. A. As microwaves pass through, the molecule dipoles try to align with the electric field, causing rotation and increased kinetic energy (= heating)....In A it makes it sound like the microwaves are not absorbed.. In A the electric field does work in causing ...

19

Winging it: Microwaves heat the corn kernel which behaves like a tiny pressure cooker. Due to increased pressure, water inside will remain liquid at higher temperatures than at atmospheric pressure. So, temperature and pressure rise. If it doesn't pop, then... well, it'll stay hot for a while. If it pops, the pressure vessel is broken, so pressure inside the ...

18

Your question comes down to whether the EM absorption is a resonant process or not, where resonant means it corresponds to the energy of some excitation of the water molecule. The answer is that it is not a resonant process. Microwave ovens operate at 2.45GHz but the lowest energy transitions of water molecules are rotational transitions, which have energies ...

18

The easiest solution is to use a fiber-optic camera, i.e. one with a fiber-optic connection between the front lens and the actual camera electronics. You can easily bend the fiber (but not too much!). You can now make a small hole in the microwave (smaller than the wavelength, insert the fiber. Bend the fiber and wrap it in aluminium foil. There will be ...

16

Let $P$ be the power (in $\mathrm{Watt}$) the microwave delivers then a simple heating model can be stated as follows. The heat energy $q$ needed to heat an object is: $$q=\varepsilon mc_p\Delta T$$ where $\varepsilon$ is an efficiency factor (for food stuffs with a high moisture/water content $\varepsilon \approx 0.9 - 1$). $m$ is the mass of the object, \$...

16

First, if dielectric heating relies on polarity, why is the canola oil heating at all? Second, why is it heating as much as it is? Firstly, Canola oil is a vegetable oil, more specifically a triglyceride. Vegetable oils contain polarity, coming from the glyceride ester bonds. Secondly, the temperature increase observed in those nice experiments you ...

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