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

In summary: When two metals are joined together, the electrons in one metal will flow to the electrons in the other metal. This flow of electrons creates an electric field which opposes the heat flow between the two metals. The result is that the two metals stay at different temperatures - even when the two metals are in contact with each other.
  • #1
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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  • #2


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.
 
  • #3


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.
 
  • #4


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

1. What causes the current to flow when a metal is heated?

The flow of current in a metal when it is heated is caused by the movement of free electrons. When the metal is heated, the atoms in the metal vibrate more vigorously, which causes the free electrons to collide more frequently. This increased collision rate leads to an overall net movement of electrons, resulting in a flow of current.

2. Is this phenomenon observed in all metals?

Yes, this phenomenon is observed in all metals. The flow of current in a metal when it is heated is a fundamental property of metals, known as electrical conductivity. This property is due to the presence of free electrons in the atomic structure of metals.

3. Does the flow of current increase or decrease with temperature?

The flow of current in a metal increases with temperature. As the metal is heated, the atoms vibrate more vigorously, leading to an increased collision rate among free electrons and a subsequent increase in current flow. This is known as the positive temperature coefficient of resistance.

4. Can the flow of current be reversed by cooling the metal?

Yes, the flow of current can be reversed by cooling the metal. As the metal cools, the atoms vibrate less, decreasing the collision rate among free electrons and resulting in a decrease in current flow. This is known as the negative temperature coefficient of resistance.

5. Is this phenomenon only observed in metals?

No, this phenomenon is not only observed in metals. It can also be seen in other conductive materials, such as semiconductors and electrolytes. However, the mechanism of current flow may differ depending on the material's properties and composition.

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