Physics Help Forum Energy mass conversion in microwaves.

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 Jun 27th 2018, 01:06 AM #1 Senior Member     Join Date: Feb 2017 Posts: 205 Energy mass conversion in microwaves. As we know when the electrons are excited they move from higher energy state to ground state causing electromagnetic radiation. Now EM radiation in form of microwaves is Energy. Where has this energy come from. From the mass of the electron?
 Jun 27th 2018, 02:27 AM #2 Senior Member     Join Date: Jun 2016 Location: England Posts: 882 The energy is "stored" in the relationship between the electron(s) and the nucleus. The additional energy of the electron causes a form of "tension" between the electron and the nucleus, which is released when the electron re-emits a photon You might like to try an E=mc˛ calculation to see what sort of mass change you would be looking for due to an atom absorbing a photon. Note that the energy levels for electrons in an atom are generally outside the microwave region of the EM spectrum. Microwaves energise the bonds between atoms. __________________ ~\o/~
 Jun 27th 2018, 02:27 AM #3 Senior Member   Join Date: Oct 2017 Location: Glasgow Posts: 366 It comes from the Coulomb potential energy.
Jun 27th 2018, 04:51 AM   #4
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 Originally Posted by Woody The energy is "stored" in the relationship between the electron(s) and the nucleus. The additional energy of the electron causes a form of "tension" between the electron and the nucleus, which is released when the electron re-emits a photon You might like to try an E=mc˛ calculation to see what sort of mass change you would be looking for due to an atom absorbing a photon. Note that the energy levels for electrons in an atom are generally outside the microwave region of the EM spectrum. Microwaves energise the bonds between atoms.
So you mean the electrical potential energy that causes a tension between the electrons and the nucleus is a form of energy that acts as a string causing tension between the electrons and the nucleus. Now this tension releases and a photon or microwave is emitted which converts to thermal energy when in a microwave Owen because of polar charge of water.

So that means that it's a conversion from electrical potential energy to a photon or microwave which is again another form of energy.

 Jun 27th 2018, 05:17 AM #5 Senior Member     Join Date: Jun 2016 Location: England Posts: 882 That is the basic idea, There are a lot of nuances that your simple summary glosses over but as a starting analogy I have seen worse. __________________ ~\o/~
Jun 27th 2018, 05:59 AM   #6
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 Originally Posted by avito009 As we know when the electrons are excited they move from higher energy state to ground state causing electromagnetic radiation. Now EM radiation in form of microwaves is Energy. Where has this energy come from. From the mass of the electron?
Yes it has. If you compress a spring you do work on it, and you increase its mass. Now, you might say the "spring" in your scenario is the atom as opposed to the electron, but if that atom is a hydrogen atom consisting of an electron plus a proton, that's all that's there. The mass of those two things vary.

It's similar for binding energy, where's there's a mass deficit. See Wikipedia: "A bound system is typically at a lower energy level than its unbound constituents because its mass must be less than the total mass of its unbound constituents". When an electron and a proton move towards one another to form a hydrogen atom, a 13.7ev photon is emitted. The mass of the electron reduces, as does the mass of the proton. However because the proton is 1836 times the mass of the electron, the electron loses most of the mass. Don't think that the electron mass and the proton mass stay the same whilst some negative-energy thing called binding energy is created. The negative energy of binding energy is because there's less mass-energy present in the system. The system comprised of an electron and a proton and nothing else.

Jun 27th 2018, 07:05 AM   #7
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 Originally Posted by avito009 So that means that it's a conversion from electrical potential energy to a photon or microwave which is again another form of energy.
Yes. As Farsight indicates correctly in his post, there's additional theory that can explain more precisely what's going on, but at a high-level, that pretty much sums it up.

Just be careful when talking about potential energy because orbital electrons are a very unique beast indeed compared to other phenomena that involve potential energy. The best way of understanding what's happening in more detail is to get an introductory QM book and start looking at some of the problems physicists experienced in the past, like the ultraviolet catastrophe. You can then start looking at stuff like the Bohr model of the hydrogen atom and move on from there.

Last edited by benit13; Jun 27th 2018 at 07:09 AM.

Jun 27th 2018, 09:37 AM   #8
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 Originally Posted by benit13 The best way of understanding what's happening in more detail is to get an introductory QM book and start looking at some of the problems physicists experienced in the past, like the ultraviolet catastrophe. You can then start looking at stuff like the Bohr model of the hydrogen atom and move on from there.
If I had my way benit, the Bohr model would be consigned to the flames. IMHO it teaches the wrong concepts, and it's difficult to then teach the right concepts. Like the way nature of matter, and how the electron in an atomic orbital has less kinetic energy than the free electron.

 Jun 27th 2018, 01:26 PM #9 Senior Member   Join Date: Jun 2010 Location: NC Posts: 417 Microwaves do not "Heat." In the microwave, one does not "heat" coffee to a higher temperature. The mechanism is not "heat", is not energy transfer from a higher temp- erature to a lower temperature. The microwave effect is "frictional work." Here is an energy equation analysis... Microwave Coffee | THERMO Spoken Here!
Jun 28th 2018, 12:45 AM   #10
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I'm sorry to pour cold water on this discussion but microwave emission/absorbtion is not directly due to the electrostatic potential energy of an electron in the field of the nucleus.

Most atomic spectra transitions take place at much higher energies ie visible light, uv light and x rays.

Microwave and infra red transitions lie in the province of bond activity in molecules.
That is more than one nucleus is involved.
These transitions may be due to molecular rotations, bond stretching, bond waggling and so on.

Here is a very basic chart illustrating this.

If you think about it, the energy can't come from the atoms or they would fall apart.
So we now answer the OP's rather more perceptive question.

 As we know when the electrons are excited they move from higher energy state to ground state causing electromagnetic radiation. Now EM radiation in form of microwaves is Energy. Where has this energy come from. From the mass of the electron?
The energy comes from what ever makes the molecules vibrate about their bonds.
This may be thermal, an external field as in NMR and so on.
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Last edited by studiot; Jun 28th 2018 at 01:04 AM.

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