How does a microwave work?

Question

I was told a mcrowave works on sound energy focused on water molecules to generate heat. If true,where does the elecrical appearing reaction with metal come from?

Answer 1

A microwave oven generates radio waves in the range of 2.5 gigahertz. This spectrum lies between FM radio waves and infrared rays, the latter of which border on detectable light at the red end of the visible light spectrum. Radio waves in the microwave range have favorable properties in that they are absorbed by food – or liquids, fats and sugars.

When food in a microwave absorbs radio waves, the energy translates into atomic motion, which becomes heat. In other words, microwave radio waves excite the atoms that make up food. This results in evenly and quickly cooked food, all things being equal. In reality, some types of food do not allow equal penetration of radio waves, resulting in “cold spots.” This is a concern with poultry, meat and eggs, where bacteria can survive in the uncooked areas.

Answer 2

A microwave oven is essentially a metal box that acts as a resonant cavity for microwaves. Microwaves are electromagnetic waves like radio, infra-red, visible light, ultra-violet, and x-rays, and fall between radio and infra-red on the electromagnetic spectrum. Most typical microwave ovens have a device called a magnetron tube that will oscillate (produce an electrical sine-wave waveform) at a frequency of approximately 2.4 GHz. The electrical energy travels down a wave-guide to a metal plate on the inside of your microwave. This plate is an "antenna" that radiates the 2.4 GHz energy into the interior of the microwave. Food that contains water absorbs this Electromagnetic energy and is warmed. Because water is a polar molecule, it will rotate to allign itself with the microwave passing through the food. This electromagnetic interaction between the passing microwave, and water molecule's own electric field is how energy is transfered to the food.

When you put a peice of metal in the microwave, the passing electromagnetic wave will cause large electrical currents to flow on the metal object's surface, and the metal will get hot very quickly.

Another issue with microwaves is the impedance match. If you run your microwave empty, it is actually harder on the magnetron than heating a large peice of food. This is because, if there is nothing inside the oven to absorb the microwave energy, it gets reflected back and dissopated inside the magnetron tube (as heat).

Answer 3

A microwave actually gets its name from the energy it uses. Microwaves are electromagnetic waves which come between radio waves and infra-red on the electromagnetic spectrum.

The radiation goes into the food and is absorbed by substances such as water. The radiation causes a reaction that creates heat and cooks the food.

Metal objects in a microwave can cause sparks (an electrostatic discharge), apparantly this is caused by an electric field forming which exceeds the dielectric breakdown gradient of air and causes sparks to form.

So in other words, I think it means that at a certain point, there is too much electricity built up in the metal and the air stops insulating it, which is when you see the sparks.

Answer 4

simply put a microwave emits "microwaves" set at a certain frequency so that the waves frequency vibrates the water molecules in what ever is in the microwave (thats why your container doesnt heat up cause plastic or ceramic dishes dont have all too much water in the if not at all) and when you get vibrating molecules in a substance those molecules hit other molecules and the "kinetic energy" of the substance raises when kinetic energy rises the temperature rises. BAM hope that helps

Answer 5

No, microwaves are light waves, not sound waves. They are at the right energy to vibrate the water molecules in the substance that you are trying to microwave. The water molecules vibrating increases their kinetic energy, increasing the heat of the material. That's why microwaving things with very little water component doesn't work very well.

Answer 6

If i'm not mistaken, a microwave works by exciting atoms in the substance being microwaved. In organic molecules (aka food), the organic molecules will absorb microwaves at specific wavelengths, and vibrate faster. This faster vibration is what gives food more heat. When metal atoms absorb microwaves, their electrons are excited into new orbits, and when they fall back energy is released as photons, which we see as flashes of light. Again, not sure about this info.

Answer 7

I don't have a complete answer for you, sorry.
The principle that the microwave heats water molecules is correct. It uses (as the name suggests) microwaves, which are like light waves but with muuuuuuuch longer wavelengths. On the other hand, "sound energy" (there really is no such thing, sound has nothing to do with energy transfer) is just a common term for the result of air compression, and has nothing to do with a microwave oven.

Answer 8

A microwave works by bombarding what ever has been put in it with microwaves. which are a form of EM (electromagnetic) radiation, with similar wavelenght as the separation between the water molecules contain in food. Since the separation between the molecule are similar to the microwave's wavelenght, the microwave causes the molecules of the water to resonate, transferring the maximun energy, in the form of kinetic energy which in turn exciting the molecules and causing them to vibrate, changing the kinetic energy into thermal energy, which in turn heats you food.

Answer 9

Right, basic chemistry to start with. Water is a polar molecule. It has a different charge in the middle relative to the ends. What a microwave does is create a magnetic field, which is constantly reversing at a very high speed. This causes the water molecules to flip over, and back, over and over again at great speed. This causes friction, which in turn creates heat, and Hey Presto, your pizza is nuked!

Answer 10

Put simply a microwave oven generates electromagnetic radiation of a frequency which is the resonant frequency of the -OH end of a water - or similar molecule. They will heat chocolate and fat for example neither of which contain water.
The vibration 'friction' produces heat which heats the food.
RoyS.