Comment: When a metal is heated, there is current (ie flow of e) flowing too

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Discussion Overview

The discussion revolves around the relationship between heating metals and the flow of electric current, particularly focusing on the mechanisms of heat conduction and the thermoelectric effect. Participants explore concepts related to electron movement, temperature, and the Seebeck effect.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant asserts that heating a metal causes a flow of electrons, which they equate to electric current, as energy is transferred from one end of the metal to the other.
  • Another participant introduces the thermoelectric effect, suggesting a practical application involving a thermocouple made from copper and constantan wire to measure e.m.f. at various temperatures.
  • A different participant challenges the initial claim by stating that while electrons are involved in heat conduction, there is no net current because electrons move in both directions, resulting in an average balance.
  • This participant also emphasizes that temperature in solids refers to the lattice (phonons) rather than the electrons, and notes the significance of electron-phonon scattering in heat conduction.
  • Lastly, a participant identifies the Seebeck effect as a specific phenomenon related to thermoelectricity, attributing its discovery to scientist Thomas Johann Seebeck.

Areas of Agreement / Disagreement

Participants express differing views on whether heating a metal results in a flow of current. While some support the idea of electron flow correlating with current, others argue against it, leading to an unresolved discussion with multiple competing perspectives.

Contextual Notes

Participants reference concepts such as electron-phonon scattering and the distinction between the behavior of electrons and the lattice in metals, indicating a nuanced understanding of thermal and electrical conduction that may depend on specific conditions.

klng
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Comment: "When a metal is heated, there is current (ie flow of e) flowing too"

"We all know that metals are good conductors of heat. When one end of the metal is heated, the electrons will rapidly transfer the energy to the other end. This energy transfer often involves the flow of electrons from one end of the metal bar to the other. And since we know current is the rate of flow of electrons, the fact that there IS a flow of electrons (in the conduction process) means that current is actually flowing in the bar."

Any comments for the above paragraph?
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Its called the thermoelectric effect. Its make for a lovely practical. Join a piece of copper and constantan wire together and immerse in a ice bath, room temperature and then a water bath and various temperatures up to 100 Celsius. Use a current balance to determine the e.m.f provided at the various temperatures and you have a callibrated thermocouple. Neat.
 


The fact that electrons are involved in heat conduction in metals does not mean that there is a current flowing, simply because there will -on average- be the same number of electrons moving in both directions.
Also, when we talk about the temperture of a solid we are effectivly referring to the temperature of the lattice (i.e phonons); not the electrons. In a real metal the electrons are scattered so often that they never actually travel in any particular direction for very long; there is a constant exchange of energy with the lattice.
Remember that if there were no electron-phonon scattering the metal wouldn't get hot at all (in the conventional sense).

(if the scattering rate is low enough it is actually possible to create a situation where the temperature of the electrons is significantly higher than the temperature of the lattice).

The thermoelectic effect is different, because it involves TWO metals; the effective "device" is actually the junction between them, no the individual metals.
 


Its called 'THE SEEBECK EFFECT'
SCIENTIST SEEBECK have observed this first of all!
 

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