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Thread: Energy and Temperature Question...

  1. #1 Energy and Temperature Question... 
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    Okay so if raising the temperature of a substance increases the movement of the molecules, then increasing the movement of the molecules would also increase the temperature. To do this you can use microwaves- hence how we cook our food.

    And we lower the temperature and it slows th emolecules down, then slowing the molecules down would decrease the temperature.

    BUT then what would we need to use to sow the molecules down???

    Macrowaves? (wavelength higher than 10^4)?

    Some other aternate electromagnetic method?


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  3. #2  
    Forum Senior anand_kapadia's Avatar
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    just lower down the temperature might be refrigerator.


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  4. #3  
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    Yeah I understand that, but I'm looking to slow the molecules down with the result being a drop in temperature, not the other way around.

    Raising the temperature make the molecues speed up. This would be like your home oven. The reverse would be speeed up the molecules and raise the temp of the item up. That would be a microwave.

    Lower the temperature slows the molecules down, that would be a fridge. But what would slow the molecules down and thus lower the temperature?

    I'm loking for a solution that would do this electromagnetically.
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  5. #4  
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    Right, eh how to start. I really dont think you get the idea behind this. Tempreture is basically just a measurement like volume or mass. It is a measure of the average kinetic energy of a sample of atoms or molecules. It has no physical form it is not a thing but a measurement. By increasing the tempreture you are not causing the increased speed of atoms. Tey are one and the same if you understand. You cannot increase the tempreture of a substance without increasing the speed at which the atoms move as that IS what tempreture measures. They are not two seperate things, one is a physical property (the kinetic energy of atoms) the other is it's measurent (tempreture C/F/K).UNless i didnt understand you thats how i thought you saw it.

    As for microwaves, the frequancy of an electromagnetic wave photon is proportional to its energy E=hf where h is Planks constant. Electromagnetic waves can be thought of as pure energy as they have no mass.The reason microwaves increase the speed of the atoms and this is only in water no other molecule as far as i know does this. Is because in atoms they have energy levels of electrons and these electrons can move outwardly when energy is given to them. This requires an exact amount if energy. This can come from an electromagnetic photon but the photons energy must be eqactly the amount of energy required by the electrom to jump levels no more no less. One exact energy = one exact frequancy. This single frequancy lies within the microwave part of the spectra and is used to cook food by "giving" its energy to electrons in atoms so increasing the energy of the atom which is used in its movement so increasing the tempreture reading telling us that the atoms kinetic energy has increased. Any other e.m.w. cannot do this to this atom as it does not have this exact energy equivilant shown by its frequancy. So therefore as this is the way e.m.ws can heat up substances you can therefore see how there is no way it can take away energy. Thats just not how the process works if you understand what i mean.

    Thats pretty long and to understand it you need to more about the surrounding areas i would suggest reading other materials as what iv told you is pretty shortcut but the short answer is no electromagnetic waves can in no way absorb energy from atoms. When an atom loses energy it is from convection or conduction or in the electromagnetic way which is to lower its electron back down a level recreating the same photon used to "push" it up and emitting it away.
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    hey, a very right explanation indeed :P
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  7. #6  
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    well temperature is essentially a measurement of th engery, so raisign the temperature aka increasing the energy would be making the molecules speed up and vice versa with removing it.

    Basically I'm looking for a way whether proven or not (since the research s for a science fiction film) to make a device that would act as a reverse microwave and make items put in it cold really fast. (and not like a fridge as that takes more time, the way an oven takes more time to cook things than a microwave does).

    What's a good theory/probably explanation of creating such a device whether it would work or not. I'm just trying to do my due diligence.
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  8. #7  
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    no because electromagnetic waves cannot absorb energy it would never work
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    Since we are talking science fiction, maybe you could have something analogous to noise cancelling headphones. These work by generating a sound out of phase with the noise so it cancels the noise by destructive interference. Destructive interference also works with electromagnetic waves. The fly in the ointment in the real world would be that the molecules are not vibrating in phase but randomly.
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    well we want the molecules to not move at all, like when in a frozen state, or to align in a crystallized formation, no?

    is there a way to surround it by a certain type of energy field to cause the molecule to align and then cease moving? (seeing as how the opposite polarity of the microwaves is what causes them to move in the heating scenario)
    http://www.gallawa.com/microtech/howcook.html
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    for one thing, ceasing all motion is absolute zero...not freezing. No one has made it to absolute zero, best wiht in a few degrees or so.

    About the idea that only water can absorb microwave energy is false -- many materials are lossy with respect to a microwave signal where they will heat up when the wave is passed through them. You take a material like balsa wood, that will heat up when microwaves are passed through it -- even dried out balsa wood.

    From a science fiction standpoint, I do feel leaps of faith can be made, and I like the idea of destructive interference, like the mentioned noise canceling headphones. I mean, Batmab begins has a HUGE incorrect idea on microwaves, and that didn't necessarily hinder the story. I mean, it's science fiction, you want to get it somewhat accurate, but the imagination is part of. Back to the Future is all sorts of incorrect science -- but the movie series rocks regardless.

    I also am not so sure it's appropriate to view microwaves as a photon model, since they aren't nearly high enough frequency for that approximation to describe microwave/matter interation.
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  12. #11  
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    I didnt mean microwaves as a whole i meant the frequancy in which you get in your standard microwave oven as the example he gave is the one which heats water molecules. If this occurs in balsa wood at the same frequancy it would suggest carbohydrates have similar energy levels to water which regarding their great differences in composition and structure i would doubt they were the same. Mcirowaves are a section of freqancies and im sure that for each freqancy there is some atomic structure that would absorb it.

    As for microwaves since all electromagnetic waves are photons and microwaves are e.m i would see no reason why they would not travel as photons too. They have all the same qualities as other e.m.w so must have the same properites too.

    As for the sound thing interferance only happens with electromagnetic waves as far as i am aware. Sound waves are not electromagnetic and they are in everyway far different from e.m.w in their compositin and the way they travel. They do not have interferance in the same way as they do not have diffraction or refrection or reflection. Causing destructive interferance in e.m.w would not cool a substance, in fact it would have no interferance on it at all unless it was canclling out heat irradiated to it in that case its tempreture would either still be variable due its lose of heat or it gaining heat in other ways.
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    For one thing, water is not necssarily the most absorbant material to microwaves at 2,4GHz -- that would be at the resonance frequency of water around 25GHz or so. They have a high loss tangent, though, so I am not saying water is not a good absorber.

    See, you can make that argument then that the 60Hz AC power travels as a photon because it is an electromagnetic wave. I see your point, but I have never seen anyone talk about it in terms of photons. Even something like geometric optics used in microwave propagation theory is not saying it acts like a photon, and that involves ray theory.

    Sound can definitely have interference, and sound can diffract -- place a speaker in one room and stand out the door -- you can hear the sound and th e sound waves spread away from the doorway -- diffraction. Sound cancellation work by outputing a 180 degree phase shifted room noise signal to that that is actually reaching the ear, and that does cause cancellation of the sound. It's not perfect, but it is a reduction in sound level.

    I agree that I don't think this is actually a technique that will cool down a substance, but I do think it is plausible enough to make a science fiction movie on. You don't actually need to invent a method of doing this in order ot make it part of a story. That was my point.
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  14. #13  
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    What about the process of laser cooling? Is that a more plausable angle to have an inventor experimenting with to create a reverse microwave oven that cools things really fast?

    http://www.colorado.edu/physics/2000/bec/lascool1.html
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    Laser cooling is actually something that has been experimentallly verified. That is plausible. You'd still have to take some liberties in making it into a smaller microwave-sized device and all that, plus it's usually for a gas and not like a slice of pizza.....
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    I'll have to look into the laser cooling angle more. it seems like a more reasonable leap of faith on behalf of the viewer than "macrowaves" etc.. and I'm only going for the kind of accuracy required to make a good kid's movie like Explorers etc...

    I still wish there was a way to explain removing engery from a solid or liquid object that would cause the molecules to slow down and thus drop it's temperature.

    Oh and sholla... who wants cold pizza? :wink:

    I guess I'll start with this...
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    I appears to be something that cools the surface down to a cold temperature, then just relies on conduction to suck the heat out of whatever you place on it. It isn't using anything electromagnetic here.

    This can be done various ways using refrigeration techniques.

    Have you ever seen an induction stove-top? It's basically a stove top that never gets hot -- it uses magnetic induction to induce current, and therefore generate heat, in a cooking pan. if you turn it on and don't put a pan on it it will never heat up.
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