How do Microwaves Work?

[ugochukwu]

I understand a few things about microwaves that i am not sure if my source of information is really correct. Food is heated in the microwaves when water molecules in the food vibrate. Could you guys give me more information on how Microwaves work and why the reject materials that conduct electricity? Help will be appreciated

[aommaster]

ugochukwu said in post # :

I understand a few things about microwaves that i am not sure if my source of information is really correct. Food is heated in the microwaves when water molecules in the food vibrate. Could you guys give me more information on how Microwaves work

 

That, i can help u with.

 

ugochukwu said in post # :

why the reject materials that conduct electricity? Help will be appreciated

 

That I can't

 

 

 

Well, when microwaves are beamed down onto the food, like you said, the water molecules obsorb it and start to vibrate. This causes an energy change from kinetic (movement) to heat. This is what warms ur food up.

 

If yo put an empty plastic bowl in the mocrowave, there is no water in it, which means that it does not heat up. It may heat p slightly however, because mostly everything u have contains a tiny bit of water in it.

 

Hope that helps

[Radical Edward]

when you put a metal conductor in a microwave, you create a large potential difference between different points on the surface, causing electricity arcs between them.

 

the frequency of microwaves is basically the same as the resonance frequency of water.

[Crash]

Originally posted by aommaster

 

This causes an energy change from kinetic (movement) to heat. This is what warms ur food up.

 

Hope that helps

 

heat is kinetic energy,

you can actually measure the length of the microwaves if ya want this is how ya do it.

1) stop the glass dish inside from rotating when the things turned on

2) get a hole bunch of marsh mellows and put them closely packed next to each other and then leave it on for bout minute i think

3) measure the distances between the highly metled points and thats the lenght

=)

[aommaster]

Doesn't the kinetic energy CHANGE to heat energy? Kinetic energy is movement, and heat is.... heat!

[Skye]

How do you explain heat energy in terms of molecules without it involving movement?

[aommaster]

well...:shrug:...

 

 

 

ok. You got me!

 

But then, why are we taught that it was a different form of energy? And what about Infrared radiation, THAT is heat as well!

[Dave]

Crash said in post # :

you can actually measure the length of the microwaves if ya want this is how ya do it.

=)

 

Easiest way is to read the manufacturer's booklet or sometimes it's on the side of microwave.

 

This method also prevents you having to clean up a rather large mess from exploded/molten marshmellows

[aommaster]

What difference is there if the microwaves are shorter/longer?

[Dave]

You may be familar with a very famous equation, E = hf, where E is the energy of a photon, h is Planck's constant (6.63x10^-34) and f is the frequency of the photon. We also know that c = f*lambda (c = speed of light, lambda = wavelength). So E = h*c/lambda.

 

So for microwaves with a shorter wavelength, the energy they have is going to increase, and for microwaves with a longer wavelength, their energy will decrease.

 

(Please note: I haven't done Physics for about 6 months now, so my definitions and explanations of the equations might not be entirely right )

[aommaster]

oh ok. Does that mean that they heat up the food faster, because they have more energy in them?

[wolfson]

In microwave cooking, the radio waves penetrate the food and excite water and fat molecules pretty much evenly throughout the food. There is no "heat having to migrate toward the interior by conduction". There is heat everywhere all at once because the molecules are all excited together. There are limits of course. Radio waves penetrate unevenly in thick pieces of food (they don't make it all the way to the middle), and there are also "hot spots" caused by wave interference, but you get the idea. The whole heating process is different because you are "exciting atoms" rather than "conducting heat".

 

In a microwave oven, the air in the oven is at room temperture, so there is no way to form a crust. That is why foods like "Hot Pockets" come with a little cardboard/foil sleeve. You put the food in the sleeve and then microwave it. The sleeve reacts to microwave energy by becoming very hot. This exterior heat lets the crust become crispy as it would in a conventional oven.

 

(http://home.howstuffworks.com/microwave.htm)

[aommaster]

oh ok! Thanx

[wolfson]

yw look at website for futher info.

[aommaster]

I use that website quite a lot, amazing that i hadn't had a look at it this time

 

Something out of topis, i had answered ur maths challenge, please check whether it is correct or not!

[YT2095]

you may even forget that it`s microwaves, consider it Photons

as you know Infrared light (photons at that frequency) cause a surface warming effect, like when you sit in front of a fire

then think of Radio waves, they can transmit energy through alot of materials and if enough power is used, it will create a heating effect.

NOW, think about a good mix between the 2, because frequencies higher than normal radio and lower than infrared puts you right in the middle of the ....... you guessed it MICROWAVE band

and so you get the best of both worlds, a good heating effect due to the packet energy (quanta) and the penetrating power of radio waves

 

a typical MW runs at about 2.4 Ghz, I can`t comment on the molecular vibration of boiling water as to its accuracy however.

[Cap'n Refsmmat]

2.4 ghz? That's my phone frequency! I doubt my phone can microwave things.

[Crash]

In large enough amounts, thats why there was that scare about phones causeing brain cancer cause they microwave your brain

[booper54]

Cap'n Refsmmat said in post #17 :

2.4 ghz? That's my phone frequency! I doubt my phone can microwave things.

 

 

I believe that's also why there is static on your phone if you're talking on it at the same time that your microwave is running.

 

As for your question about heat being different from kinetic energy, the temperature of something is the average kinetic energy of the molecules... so that must be why heat and kinetic energy are essentially the same thing.