Microwaves are essentially super high frequency radio waves and share many things in common with RADAR. A relative of microwaving is RF welding of plastic films and sheet material or making hollow cell sheets and plating for aircraft control surfaces. It’s called RF (Radio Frequency) welding and it’s very fast and reliable. I used to make sign banners, and awnings using this system.

If RF field is strong enough it is called Induction field welding and is commonly used in continuous high volume production line welding of large diameter oil pipes, and thick walled process piping. There is no need to have thousands of feet of welding rods or fluxes. This is very efficient and very clean from a safety point of view.

A2A.

As many have noted, the microwave oven heats up objects by providing them with ample microwave “light” at 2.5 GHz, which they subsequently absorb and heat up. Since we are most interested in heating up food, and this food is made of water, the maximum temperature of a substance in the microwave oven is near 100 C. But if a different object that absorbs microwaves were to be used as the “target” the oven would reach much higher temperatures.

Enter ions/electrons. Free electrons will absorb microwave radiation. Since electron gas has small mass, it heats up rapidly to reach immense temperatures. What I’m talking about here is plasma. White-hot plasma is at several thousands of degrees, or higher. This is one reason why plasma is used as the ignition substance for fusion reactors. In some cases microwaves are used to ignite the plasma itself! Thus the microwave radiation leads to immense temperatures, well beyond 100C. But is this a fair answer to the question? Afterall, the asker is probably talking about household microwave ovens. Well, you can create plasma in the microwave oven by irradiating a crumpled piece of aluminium foil. The “sparks” that emanate are plasma at several thousands of degrees. Or, as we’ve recently shown, you can actually generate a hot plasma from water-containing objects such as fruit. How hot do you think the microwaved objects in these photos?

(grape and hydrogel bead in a household microwave oven)

(two grapes in a houshold microwave oven)

The microwave effect, which was ultimately used for microwave ovens, was discovered when a radar technician got into the beam of a powerful radar system and the microwaves melted a candy bar that was in his pocket. One of my jobs in the US Air Force was operating and maintaining automatic tracking radar and missile guidance systems. Not wishing to have our bodies affected by those powerful radar beams we avoided getting in their paths at close range.

Since I don’t know of any company has made a microwave oven large enough to accommodate an adult human, I don’t believe that they are a hazard to people. If I found such a huge microwave oven I certainly would not get inside of it, just as I would not get into the path of powerful radar beam. It would have the potential to cook me.

A microwave OVEN (a microwave is an electromagnetic kind of radiation and not a machine) delivers power but it does not produce any PARTICULAR temperature. This is in contrast to conventional electric (with hot resistors supplying the actual heat) or gas heated ovens. These produce a range of temperatures controlled by a thermostat suitable for cooking.

The microwave oven delivers the power and the item being cooked gets heated by absorption of the power. For water loaded stuff like meat or bread, or whatever, the first limit to temperature is the heating up and eventually evaporation of the moisture, so for some time there is a stop in the increase of temperature around 100°C until the moisture is gone. After that further heating is possible and what is being heated becomes hotter and hotter until some new process sets in, like burning. Also possible is that the material develops characteristics so it only weakly absorbs additional microwave energy and further rises in temperature stop.

To give a couple of concrete examples, I once heated a frozen dinner roll (A bun which is basically a small loaf of bread). The thing turned to charcoal inside while looking quite OK outside. That takes a pretty fair temperature, but try to burn the inside of a roll while preserving the outside when using a gas oven.

Another example, for teaching purposes we sometimes put a pencil lead (maybe in a pencil but often without the outer wood) and this becomes hot enough to glow red when we stop for safety reasons. Here we may be talking about more than 600°C and still hotter available on demand! In short, the item in the oven just gets hotter and hotter until the heat radiated equals the power delivered by the oven or the item is destroyed. There is no particular temperature associated with this method of heating.

The statement of “..microwaves heat the water” thus temperature is limited to the boiling point is not complete. Actually microwaves operate in frequency range that is not the most efficient for heating water by vibrational losses but was chosen for other historical reasons. One story given was that Raytheon had the tooling left over from the war for the tubes when it was decided to get into the food microwaving business.

Secondly, the vibrational friction loss is not the only sort of loss (heating. You can have pure electrical current flow voltage drop across the ionic components of the food that also ends up as heat in the food. You can easily burn bacon with a microwave and by that time all that is left is fat in the food. But after it carbonizes, then resistive heating will suffice to carry it on and set fire to it.

Further proof of other heating mechanisms abound on YouTube. For instance, put steel wool in a microwave you don’t care about and it will quickly catch fire from the resistive heating . No water. Put an old unwanted silver colored CD in the microwave and it will sparkle and perhaps flame due to resistive losses. Again no water.

Small microwaves are capable of a few hundred watts of microwaves to bigger units capable of a kilowatt or more. A 60 watt soldering iron can easily hit 700 or more degrees Fahrenheit. So imagine what 10 to 20 times as much power can do.

Industrially, microwaves of other frequency can be used on pure plastics (no water) and heat them to the melting point (400 or more degrees Fahrenheit) to seal/weld them together. Here the vibrational loss mode (dielectric loss) is dominant.

Stupid bloody question, have you ever seen a microwave big enough to fit an adult human being? — Are you a leprechaun, fairy or something……………..

I hope you are not thinking that there may be ionizing radiation in a microwave oven… because there isn't.

Before any body jumps me, let me explain that there may be a tiny amount of radioactive thorium in your oven. But, this material has nothing to do, directly, with heating your food. It is in the cathode, the piece of metal which emits electrons, which are then subjected to a high voltage potential and thus accelerated past the resonant cavities to induce microwave formation. The thorium aids in the electron emission process.

Your food is heated by interactions with microwaves… duh… electromagnetic radiation of longer wavelength than visible light… which both lack the energy to ionize. The microwaves interact with the water in your food… and to a lesser degree with oil and grease.

Basically, water molecules are “polar”. Though overall neutral, they have a slight separation of charge due to the way the 2 hydrogen atoms arrange themselves around the oxygen atom with 106° separation. Orbital electrons tend to spend more time around the 2 hydrogen atoms, giving this “end” of the water molecule a slightly more negative charge than the oxygen end.

This slight polarization is enough to cause the water molecules to respond to the constantly changing polarity of the oscillating microwaves. The popular concept, and the easiest way to explain it, is to say that the water molecules “vibrate in place”. This vibration is manifested as heat.

The energy of ionizing radiation from radioactive materials would not be powerful enough to heat food. A lethal dose of gamma rays, for example, if absorbed by a person in a short period of time, is ~1000 rad. Whereas, the amount of absorbed dose of gamma to raise the temperature of 1 cc of pure water at STP by 1° C, is 100,000 rad. Not a very efficient way to cook. Your oven would have to be surrounded by several feet of lead… no upstairs apartment. To avoid getting overdosed yourself, you would have to learn how to use a long-handled L-shaped paddle to load and remove food items around a blind corner. You could never wipe up spilled soup. To create the radioactivity needed to supply billions of rad in a relatively short time, the radioisotope would have to have a very short half-life, or the source would be too large. So, you would need to refuel probably every few days or weeks… very expensive. At that high rate of activity, your source would probably self-heat and melt, unless it had a dedicated cooling system… also very expensive.

So… it's much cheaper… and safer… to use microwaves.

The question is not meaningful because the mechanism by which a microwave confers energy to the food is not traditional heat transfer process. Instead, the heat or thermal energy is actually generated inside the food itself.

Electromagentic waves stimulate certain molecules to vibrate. This vibration stimulates other molecules to vibrate; and this is how the heat is generated. Water is the most prominent of the molecules affected by this electromagnetic stimulation. In some foods when the water has evaporated almost no more energy enters the food.

However, as anyone who has had a fire start inside a microwave would know from experience, there are other molecules that continue to absorb energy once all the water molecules have evaporated and escaped. There are a number of fats that have enough polar properties to vibrate much as water does. And they will continue to heat up until the temperature of the food reaches a flammable point.

One can, however, use the microwave to steam foods by placing them in a container, adding a few tablespoons of water, and covering the container with plastic wrap or even an inverted bowl. The extra water evaporates and it cooks the food by steaming, along with the normal microwave process. In this case, the medium surrounding the food is steam and it’s probably pretty close to the boiling temperature of water… although there is some possibility that it might be somewhat hotter.

That a microwave works this way is important because it means that you cannot brown the outside of food very effectively as you might in an oven or on a stovetop. That’s the reason microwaves have earned a reputation as poor cooking tools.

That is not how a microwave works. It heats food by supplying energy to molecules, most notably water molecules. Thus, two different foods will heat at different rates. The microwave that I bought just after Christmas has an interesting and brilliant innovation, a sensor that detects when food has reached the right temperature by the amount of water vapour in the microwave. It works amazingly well and I recommend this model to anyone wanting a new microwave: Panasonic Inverter NN-ST479S. Microwave a piece of fish and a bowl of cabbage weighing the same amount and they’ll take different amounts of time because the water content is different. However, bake them in a conventional oven and while they might still take different amounts of time to cook, the relationships between the times in the microwave and the conventional oven will most likely be different.

Thus, your question can only be answered with relation to the power of the microwave oven and a specific weight and dimensions of a specified food. You could ask, "By how many degrees Celsius will 500g of fresh haddock, 1cm thick, rise if microwaved for two minutes in a 900W microwave at full power?" This question is answerable but you need all these specifications to make it answerable. Change the thickness of the fish to 2cm or change the fish to salmon and the answer will be different. Also, the model of microwave will make a slight difference too.

A microwave does not have a temperature that is meaningful for cooking times.

Since the microwave works by boiling the water in the food, all cooking is done at or close to 100 deg C.

The amount of time that time takes to cook something depends on the power setting of the oven, and the amount of food present (and how “wet” it is).

A 800W (typical range) oven, on max, can bring 355ml (1 reg. soda can) of water from 20C (room temperature) to 100C (boiling) in about

4.186(J/g)x355(g)x(100–20)/800(J/s) = 150s … about two and a half minutes.

To get the time down to 1.25 minutes you can only boil half the amount of water or you have to use twice the power (not usually available).

It’s not a setting of the temperature — it is the power, or the amount of energy you use to heat up your food per second.

The higher the power, the faster your food will heat up. Usually that is what you want: quickly heat up the meal. But there is one problem with always nuking your food on the highest power setting.

Microwaves are absorbed by your food item (that’s why it heats up). The outermost layer absorbs some microwaves, meaning that the inner layers get less of them. That’s why the bowl of pasta will be steaming hot on the outside but completely cold at the bottom and you have to stir and reheat several times to have everything heated through.

Setting the microwave to a lower power output slows down the heating process and allows the heat from the outer layers to dissipate inside. Especially when you defrost you don’t want to cook that piece of meat on the outside leaving the middle frozen. Sometimes, instead of leaving the microwave always on the highest power setting, it is smarter to reduce it and let your food heat for a longer time, but evenly.

In ovens, microwaves are generated by a secret British military black-project that the Nazis would kill for! To avoid all the 1940 bombing during WWII Battle of Britain, the secret project was moved to MIT in the United States.

The microwaves are produced by the Cavity Magnetron; the key invention which made modern radar possible, and played a large role in turning the war around, in favor of the Allies.

How do magnetrons create microwaves? During World War II, MIT university started up it’s so-called “Radiation Lab,” but the lab wasn’t created to study boring old Uranium (this was pre-A-bomb.) It was founded to carry forward the UK invention of the high-wattage radar tube. Before the inventors arrived, all the prototype magnetrons and the secret documentation had been transferred to MIT, and the physicists there were trying to figure out how the heck it could possibly work. After much hemming and hawing, finally I. I. Rabi announced, “Oh, it's very simple; it's just a kind of a whistle." And EU Condon replied, "Okay, Rabi, how does a whistle work?" Rabi couldn't explain.

But Rabi was exactly right. If we blow some air past a closed resonant pipe (or beer-bottle,) it produces a loud pure note of sound. And inside a vacuum tube, when we blast a beam of electrons across the end of a closed metal pipe, this produces an intense pure signal of microwaves. The wattage isn’t very high though. And, if a hole in the pipe lets microwaves escape, the resonance is ruined and no waves are produced.

The British invention was clever: don’t use one whistle, use six or eight of them. Arrange them in a circle, and use an ‘electron vortex’ rather than a wasteful straight-line electron beam. (Add some big magnets, and then it takes very little energy to circulate electrons in a closed ring, as opposed to creating an electron-beam from scratch with no magnets used.) The electron-stream is created with a hot tungsten filament, a high-volt power supply fires the electrons past the metal slots, and the whole tube “sings.” Run a connecting wire into one of the slots, and thousands of watts of microwave energy comes pouring out, yet even with such massive leakage, the whole process doesn’t damp out and stop working. That’s the key idea, since if our single beer-bottle has a hole in the side, it won’t whistle when we blow across the top. Solution: eight beer-bottles in a circle, pointed inwards, with a violent tornado in the center. When one bottle has a hole, the other five just dump their waves into the leaking bottle, and the siren-effect keeps on going.

The magnetron tubes in your microwave oven are still the same as the WWII secret invention, only smaller, perhaps 10cm across. Two black ceramic magnet disks (about 5cm wide,) on either side of a tiny metal vacuum chamber with six cylindrical slots in the wall, and a hot tungsten filament running down the center. The magnets make the electron beam spin in a circle, like spokes on a wagon wheel that spins at nearly the speed of light.

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• What are some fun science experiments that can be done using a microwave?
• I am pretty sure I saw a spider survive in a microwave for 2:00 minutes. How is that possible?
• Why do some foods splatter while heating in a microwave while others do not?
• Oven diodes won't give me any reading even though they are not bad. does HV diodes behave different from ordinary ones?
• Why do magnetrons in microwaves use beryllium? Would normal ceramic be enough?.
• Microwave fire over frozen raspberries. This was like a plume of fire?
• What would happen if you put ferrofluid in a microwave?

ALSO try… QUORA ANSWERS: W Beaty (mostly electricity, also Nikola Tesla)

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Is there a maximum temperature a microwave oven can heat up a piece of food?

We regularly make rock cakes in our line of work.

We first need to know the moisture content of the rocks. We weigh a sample of the rocks, and then use a microwave oven to dry them to “constant mass”.

One day long ago, I spied one of our cooks drying some nice big quartz rocks. Only problem was that he had put the timer on for way too long, and the rocks were glowing a lovely yellow colour, and the rocks had very securely fused to the glass turntable.

Probably in excess of 800 degrees Celsius.

I hope that gives some inkling of the temperatures attainable.

A microwave oven rated at 1000 Watts microwave (MW) cooking power will raise the temperature of 1000 milli liters (mL) (ONE LITER) of tap water that starts at ten (10) degrees Celsius (C) (50 degrees Fahrenheit (F)) to 17.16 degrees Celsius (C) (62.88 degrees F) in THIRTY (30) seconds of 100 percent MW power run time.

So, a good general “rule of thumb” for a 1000 Watt rated cooking power MW oven is the temperature of the food you are cooking/heating or the liquid (assuming the liquid is water-based) you are heating will rise about 6.5 degrees F for every 15 seconds of 100 percent MW power “run time”.

A practical example:

Heat a 12-ounce cup of coffee in a 1000-Watt rated MW cooking power MW oven that starts at 50-degrees F. It will take about 115 seconds to bring the 12-ounce cup of coffee to a boil (just under two minutes).

Reference: Link:

SINCERELY,

Conrad Young, Senior MW Oven Designer, TurboChef Technologies Incorporated, Carrollton, Texas, USA.

Nothing.

Microwave ovens don’t work by heating up the air. They work by heating up the food itself, agitating water molecules to raise the temperature.

In almost all microwave ovens the power delivered to the load (i.e. the food) is varied by cycling the power to the magnetron on and off by varying amounts. So low will have the magnetron off for several seconds and on for maybe one second. High will have the magnetron on all the time.

Higher up the dial, the water in the food gets hotter faster. However if you have a large dense item, the microwaves only penetrate for a few mm, and only the surface regions get hot. In such a case the lower settings are appropriate as they allow the heat to be conducted inwards. Hence ‘defrost’ is a low setting, as you’re trying to unfreeze the item without cooking the outer bits.

It depends primarily on 2 factors:

(1) The Wattage of the microwave: Microwaves come in different “Watts.” This is a measure of the power of the microwave, or the amount of energy it can deliver per second.

(2) The heat capacity of whatever you are trying to microwave: Different materials change temperature at different rates as they absorb heat.

Take this example as a reference for the kinds of timescales we’re looking at:

Water has a heat capacity of about 4 J/(g*C) [Joules per gram-Celsius]. An average microwave oven has a wattage of about 800 J/s. How long will it take 100 grams of water to go from 25 C to 100 C in the microwave?

(4 J/(g*C))*(100 g)*(100 C - 75 C)/(800 J/s) = 37.5 s

So you’re looking at about 40 seconds before 100 grams (about equal to 100 milliliters) of water starts boiling!

On the other hand, the heat capacity of aluminum is about 0.9 J/(g*C). You can think of heat capacity as a substance’s “resistance” to temperature change. Clearly aluminum’s resistance is much lower than that of water. Let’s see how the time changes for 100 grams of aluminum:

(0.9 J/(g*C))*(100 g)*(100 C - 75 C)/(800 J/s) = 8.4 s

Yikes! It looks like the temperature of aluminum will shoot up much faster than water. In most cases, microwaves heat the water in food to make them warm. But if any aluminum in the microwave, it’s temperature will skyrocket really quickly! This can cause a fire. That’s why you shouldn’t put metal objects in the microwave.

They don’t emit heat, the emit frequencies in the microwave range. Specifically those 2,450MHz as required by law. And no more than 5mW per square cm measure 5cm from the oven surface.

A physically larger Microwave can put more energy into the space overall, but still limited to the same amount per unit area.

This means they’re affectively the same per unit area, but ones with larger unit area can cook more food in the same amount of time. There are some lower powered units, that can cook a little slower.

That said, I wouldn’t refer to them as being hotter or colder as the heat comes from the vibrating of the water molecules in the food from the energy emissions, and not directly by radiating heat.

Microwave ovens work differently than conventional ovens. In a conventional oven, air is heated to the selected temperature, and the heated air does the cooking. The hotter the air, the faster it cooks. Too hot, and the outside will scorch before the inside is done. Not hot enough, and it takes too long and dries it out.

A microwave oven uses microwaves that heat the food directly, no hot air needed. Cooking speed can be adjusted either by switching the microwaves on and off, or by changing the intensity of the microwaves. That’s what the low / medium / high settings are for. Since most of the microwave heating is near the surface of the food, it can take time for the heat to cook to the center, a lower heat setting gives it more time, avoiding an overcooked outside to get a fully cooked center.

So. it really depends on the size of the cake. Small mug sized cakes can cook quickly on “high” as the center gets cooked fairly quickly. Larger cakes should probably be done on the “medium” setting, allowing more time for the heat to penetrate to the center. Also, use a microwave safe pan (glass, ceramic or heatproof plastic), not a metal pan. Microwaves can’t penetrate metal, so a metal pan would result in a cake done on the top but raw on the bottom.

Hi..

This hard to answer, you are equating a microwave oven to a conventional cooking oven...

The Microwave oven doesn’t get hot, the food or liquid in the path of the micro-waves produced, absorbs the energy, and the food gets hot and hotter, as it absorbs the energy of your microwave.

Maybe do a simple experiment, put a simple food, or maybe a sandwich in the microwave…cook for maybe 30 sec…Feel the heat of the food, notice the inside box not hot at all..

Now cook another sandwich for about a min…the food should be hotter, the inside box should be fairly cool.

Cook one last sandwich, 2 min…the food should be really hot, probably smoking some, if you have cheese, it will be melted all over. The box will still be fairly cool, maybe heating up some from the steam, the food gives off…

People burn popcorn like this all the time and have tripped a fire-alarm a couple of times at work, putting popcorn in the Micro-Wave and forgetting about it, though corn/oil/paper (take out the paper, it won’t heat up because there is no moisture in it and therefore nothing to absorb the microwaves) seems to burn, the box stays fairly cool, and usually needs to be cleaned to get the greasy smell out and off the inside..

I hope this helps…

Dave

Don’t think of cooking temperature when you think about microwave ovens. Microwaves heat the food that’s in them and will keep heating it as long as the microwave oven is on. Usually there is some limit of 100°C, which is a boiling point of water, but when that area of the food becomes dry, the microwaves can continue heating it until it chars and may even catch fire. We have reached temperatures over thousand degrees Fahrenheit in one of our ovens – I won’t tell you how, because we are a research group and the sort of thing can be very dangerous if you don’t have the proper equipment & don’t know All what you’re doing.

Unlike gas or electric ovens, which rely on creating an ambient temperature for [even] cooking, microwave “ovens” just deliver power in terms of the wattage rating multiplied by duty-cycle-percentage (“power” on the oven, usually 1–10 where each number represents tens of percent) multiplied by cooking-time (result is equivalent to kWh, kiloWatthours). The resulting temperature of what is inside can be very hot. I’ve seen demos where a sheet of paper is raised to its flashpoint - ºF 451, if I recall. Its easy to raise the temperature of food to 350 ºF or more, not that you would usually want to.

Microwaves cause water molecules to go into a vibrant dance, flipping back and forth some 2.45 billion times a second this is very efficient and very quick. As you may know, microwave ovens can super heat water to a temperature well above boiling point which can be dangerous without breaking the meniscus with a toothpick or the like to break the meniscus before it is placed in the microwave to allow it to boil.

I am conflicted about whether the rate of heating increases linearly or not. My interpretation is that water heats so efficiently and quickly that it is hard to observe the stages it goes through.

Excellent question, thanks.

Originally answered: “Can a microwave get hotter than 212 F?”

Let’s keep this in sane units, shall we? So, 212 deg. Fahrenheit is 100 deg. Celcius, which is the boiling point of water.

Now, a microwave oven works by heating the food from within, so to speak, rather than heating the air around it as in a conventional oven. You would typically set a conventional oven for, say, 200 deg. C, and it will heat the air inside the oven to that temperature. After a while, the food inside will reach the desired internal temperature, which might, perhaps, be 60 deg. for a roast, or 80 deg. for chicken.

Using a microwave oven, you’ll typically set it to full power (100%), and a number of minutes cooking time. To heat a cup of tea, for example, from room temperature (20–25 deg C) to very hot (80–90 deg) will typically take around a minute and a half. If you set to 2 minutes, the tea will usually boil (which you normally don’t want). So you can argue that the microwave cannot reach a temperature of more than 100 deg C, since the tea will keep boiling at that temperature. Untill it’s all boiled away (turned into steam). At that point, it is quite possible that continued operation of the microwave will heat the (now empty) cup to even higher temperatures. If it’s a ceramic cup, it might survive this abuse. If it’s a plactic cup, it may very well melt, and even catch on fire. This could even damage or destroy the microwave. Don’t try this at home. Other foods, like popcorn, which has essentially zero water contents, may reach higher cooking temperatures.

So the answer to the question “Can a microwave get hotter than 212 F?” would be: It very much depends on what you are cooking. You cannot compare cooking temperatures directly to those of a conventional oven. Please be sure to always set the timer of the microwave correctly, in accordance with the amount and type of food you are cooking.

Microwaves do not penetrate far into food, so the outside (of a steak or a glob of mashed potatoes, doesn’t matter) may be hot while the inside is still cool, or even cold. If you let the steak (for example) sit for a little bit, the heat will penetrate the food, bringing the entire steak to an even temperature. Naturally this temperature will be lower than the initial outside temperature, so it appears to be cooling off fast.

If what you are heating is liquid or semi-liquid, like the mashed potato example above, try heating for a very short time, say 30 seconds, then stir and again heat for 30 seconds. Repeat until it’s hot through. For a solid object, like the steak, heat for 30 seconds, turn it over and wait 15 seconds and zap again for 30 seconds. The turning and waiting is the equivalent of stirring. The idea is to let the initial heat penetrate the meat before zapping again. Turning the steak corrects for the microwaves being stronger at one surface vs the other.

Bon appétit!

Microwaves don’t behave like a conventional oven and there’s no equivalent of a temperature setting. Different foods respond differently to microwaves, so the power settings are to accommodate these differences. Something you bake conventionally in a hot oven may require a high setting in the microwave but it’s also possible that it cooks best on a low setting. There is actually only one thing I know that cooks best in the microwave on a low setting and that is stuffed marrow.

I suggest that you get a recipe book of recipes using microwave ovens. Start with the one that came with your appliance and learn its individual features. Every brand is different and it can take time to learn how best to use a microwave.

The temperature for the "medium-high" setting on an Electrolux microwave oven can vary depending on the specific model. In general, this setting is used for cooking and reheating food, and the temperature can range from around 30% to 50% of the microwave's maximum power.