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Anonymous Poster

### Electrical Engineering

09/28/2010 5:12 PM

Respectable friends- I have a silly question:Strong electric current in a thin wire creates heat, what is the physical law that prevent it from being viseversa:

Why wouldn't a heated piece of copper create electric current? Like an electric motor that can be converted to be a generator,and so on?Why is it ireversible?

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#1

### Re: electrical engineering

09/28/2010 5:19 PM

Which way would the current flow?

http://en.wikipedia.org/wiki/Joule_heating

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#2

### Re: electrical engineering

09/28/2010 5:28 PM

The heat is caused by the resistance of electrons flowing through the wire (a conduductor). In reverse, when electrons are heated, there is additional energy and it makes the electrons travel in larger orbits, but not forcing them all down one path thus not flowing to make your electricty as you call it. Your questions are leading you into quantum electrodynamics – search for that on the internet and you will find many answers.

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#3

### Re: Electrical Engineering

09/28/2010 5:55 PM

Entropy.

Heat loss in a wire when a current flows is a result of work being done by the current against the resistance in the wire. An ordered state becomes a less ordered state.

In simply heating a wire and expecting current to flow, you are expecting a highly disordered state (electrons with random momenta) to become a highly ordered state (millions or thousands-of-millions of electrons deciding to move in the same general direction at the same time). Such a thing is theoretically possible, but the probability is so low you won't see it happen for a few more quadrillion years.

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#17

### Re: Electrical Engineering

09/30/2010 8:40 AM

It occurs to me that some day - in outer space - we may be able to process various metals through a liquid state - which would allow the electrons to be aligned either by centrifugal or outside electrical fields (or both) - which would - perhaps in the case where electrons are assembled - stacked - constructed in such a manner as from 'high to low density' - 'high to low conductivity' etc. which would prove relevant to the material's heating or cooling. Thanks Carlos

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#4

### Re: Electrical Engineering

09/28/2010 6:18 PM

However... a THERMOCOUPLE wire is essentially a wire that has electron flow in response to heat applied to it. Not much, but technically...

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#5

### Re: Electrical Engineering

09/29/2010 10:37 PM

You beat me to it. GA from me.

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Anonymous Poster
#6

### Re: Electrical Engineering

09/29/2010 11:30 PM

A thermocouple requires different metals that create the potential across a junction, the question was about a piece of copper, therefore heat increases random and localized electron movements. I think the earlier answers were correct.

Anonymous Poster
#9

### Re: Electrical Engineering

09/30/2010 2:00 AM

A thermocouple wire is actually 2 dissimilar metals connected in a "junction"

Anonymous Poster
#7

### Re: Electrical Engineering

09/29/2010 11:32 PM

Buenas noches efectivamente la entropia "una forma de medir el desorden de un sistema", evita la bi-direccionalidad de un proceso, tal como el aqui señalado (conversion de calor a electricidad), esta conversion no es muy eficiente pero realmente existe, tal como tambien se señala en la otra respuesta donde efectivamente el termocouple (termopar), permite que metales (junturas de metales distintos), respondan a cambios de temperatura y de calor mediante la generacion de una pequeña FEM (fuerza electromotriz--voltaje), esta FEM puede a su vez llegar a generar una pequeña corriente de cerrarse el circuito.Esto desde luego es muy INEFICIENTE (mucho calor pero poca corriente), contrario al hecho contrario de que a mucha corriente hay mucho calor.

Reciban un cordial saludo

Anonymous Poster
#11

### Re: Electrical Engineering

09/30/2010 2:25 AM

Translation of #7

Goodnight entropy actually "a measure of the disorder of a system" avoids the bi-directionality of a process, such as reported here (heat to electricity conversion), this conversion is not very efficient but it really exists, such as also noted in another response which effectively thermocouple (TC), allows metals (joints of dissimilar metals), respond to changes in temperature and heat generation by a small EMF (electromotive force - voltage), this FEM can in turn give rise to a small stream circuito.Esto close the course is very inefficient (much heat but little power), contrary to the fact that contrary to much current is very hot. Yours sincerely powered by Babelfish

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#13

### Re: Electrical Engineering

09/30/2010 5:15 AM

and in english that reads as ??

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#14

### Re: Electrical Engineering

09/30/2010 5:26 AM

See #11

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#8

### Re: Electrical Engineering

09/30/2010 12:12 AM

answering this question will really take us to fundamental view about the behavior of nature. The nature has got a mechanisms of getting into a stable state (low energy state) by dissipating energy. more often than not, systems like these (in your case... wire and heat) will find a stable state by dissipating energy in the form of heat. The next rule is: Not all processes are reversible in nature. every process has got direction for its occurrence. the process which tries to increase the entropy (disorderliness) will happen and not the reverse. after having told as above... now in the first case. flowing electric current will make the wire heated (increasing entropy or disorderliness). but the reverse is u will want all electrons to fall in a disciplined manner which which try to decrease the entropy.. so it wont happen. it will happen by adding other systems (adding one more wire as in thermo couple, joule heating)... but still the over all entropy of the systems increases in that case.

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#10

### Re: Electrical Engineering

09/30/2010 2:08 AM

what is the physical law that prevent it from being viseversa?

The Second Law of Thermodynamics.

Bioramani

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#12

### Re: Electrical Engineering

09/30/2010 3:40 AM

Precisely so. No need for the complexities of QM here.

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#15

### Re: Electrical Engineering

09/30/2010 5:58 AM

Our maths professor in college told us If a=b, then b=a is not always true. He gave an example like this: When it rains, there is thunder, but when there is thunder, it may not rain always. Please refer following : "...The Peltier coefficients represent how much heat current is carried per unit charge ... is passed through a homogeneous conductor, heat production per unit volume is: ... theory of irreversible thermodynamics (non-equilibrium thermodynamics). ..." http://en.wikipedia.org/wiki/Thermoelectric_effect

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#16

### Re: Electrical Engineering

09/30/2010 8:39 AM

Your professor was confusing an example of Logic argument with one of math.

a = b

but rain ≠ thunder

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#18

### Re: Electrical Engineering

09/30/2010 9:29 AM

Actually as corelite says what your prof said is about logic. 'If A, then B' is a statement. Valid conclusions from above are: If A is true then B must be true. If B is false A is also false. What is indeterminate is: If B is true, it does not automatically mean that A is true. Bioramani

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#19

### Re: Electrical Engineering

09/30/2010 9:42 AM

I hope your professor did not write the Wikipedia entry...

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#20

### Re: Electrical Engineering

09/30/2010 9:45 AM

Anyone forget the force applied for the ole electron to move..To get the little burger to move you have to disturb it. While heat alone will disturb it and change its numbers and formation, like the man said, it has to have a direction. Somewhat like me getting out of bed lately...

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#21

### Re: Electrical Engineering

09/30/2010 9:51 AM

The same law that prevents intelligent information for the creation of a living entity from being encoded by 'random chance' into a DNA in the random presence of all of the myriad building blocks required to create and sustain a single cell, let alone a...plant.

You can toss a pumpkin off a building and will get a useful laugh every time with an end product of mush at the bottom. You cannot, however, laugh at a pile of mush and create a pumpkin that rises against gravity to the top of the building.

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Anonymous Poster
#22

### Re: Electrical Engineering

09/30/2010 10:22 AM

Dear Friend,

Actually you might say that the converse is true as well, consider that the Seebeck effect converts a temperature difference (Hot + Cold Junction) to an EMF, this is a know and documented effect.

You might find it useful to google Seebeck effect, additionally this site will give further information:

http://en.wikipedia.org/wiki/Thermoelectric_effect

I believe that the heat generation that accompany a flow of current is due mostly to inefficiencies in the transfer of energy from valence electrons to atoms that accompany when flow of electrons. Please verify the above statement as I am not fully convinced of such inefficiencies myself.

Best regards,

M. Lakhdari

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#23

### Re: Electrical Engineering

09/30/2010 10:33 AM

Themoelectric devices (also known as Peltier devices) are solid state devices which convert thermal energy to electrical. They are simple solid state devices made with thermoelectric materials, and are used for both heating and cooling applications. See google or wikipedia for many examples. This are commercially available and fairly low cost. see http://www.peltier-info.com/

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#24

### Re: Electrical Engineering

09/30/2010 11:25 AM

you are onto something but the particulars are wrong. this is what einstein discovered that actually won him the nobel prize, the photoelectric effect, or, the other way around, the black body phenomenon. one can indeed convert energy from one form to another as you are wondering but it requires the correct substances to do that. j h waters

Anonymous Poster
#25

### Re: Electrical Engineering

09/30/2010 3:27 PM

current is created when electrical voltage is utilized.Voltage is created when a conductor

bi-sects 1milion lines of magnetic force.Heat is the bi-product of electeical consumption or usage.So heat is a result of electric use and not of electricity origin.

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#26

### Re: Electrical Engineering

10/02/2010 7:07 AM

Bioramani has hit the nail on the head - so to speak.

Usbport gives a good (analytical?) explanation - reminds me of my 100-level physics and chemistry lectures.

If you can; pick up a copy of Cengel & Boles, Thermodynamics - An Engineering Approach, 6th Ed (SI Units) and turn to page 284 for a good (intuitive?) explanation.

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