Free electron energy transfer

  • Thread starter cubozoan
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Hi forum

I need to explain the following to pupils of about 17 years of age.

2 questions regarding free electron kinetic energy transfer to copper wire (or resistor) material atoms in an electrical circuit.

1. I am confused as in which situation free electrons in a circuit transfer energy to heat a copper wire. Is it electrons that are free of their atom or electrons that jump to other outer valence bands of (copper wire) atoms?

2. How do free electrons actually transfer energy (kinetic) to (copper wire) atoms? How do they vibrate the copper wire atoms to heat the wire? Do they collide or some other mechanism?

Thank you for your time reading this. I hope I have made myself clear

Regards

Andy
 

Answers and Replies

  • #2
Drakkith
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1. I am confused as in which situation free electrons in a circuit transfer energy to heat a copper wire. Is it electrons that are free of their atom or electrons that jump to other outer valence bands of (copper wire) atoms?

The free electrons are not bound to any single atom, but are instead bound to the metal as a whole. You can think about it as having each metal atom rigidly set in place with a "sea" of free electrons around it. See here: http://en.wikipedia.org/wiki/Electric_current#Metals

2. How do free electrons actually transfer energy (kinetic) to (copper wire) atoms? How do they vibrate the copper wire atoms to heat the wire? Do they collide or some other mechanism?

Collisions with the ions.
 
  • #3
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Thank you for the replies and discussion. I feel some of the content is beyond my understanding.

I think my first question has been answred - they are both a similar thing. In both situations they still belong to a nucleus.

I need help describing how electrons (or a sea of electrons) transfer kinetic energy (being accelerated by electric field within an electrical circuit) to conductor atoms - thus heating conductor and electrons losing kinetic energy themselves
 
  • #4
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As soon as I posted a reply it seems some previous posts have vanished
 
  • #5
Drakkith
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I think my first question has been answred - they are both a similar thing. In both situations they still belong to a nucleus.

A free electron cannot be said to belong to any one nucleus. They are being shared between every nucleus in the metal.

I need help describing how electrons (or a sea of electrons) transfer kinetic energy (being accelerated by electric field within an electrical circuit) to conductor atoms - thus heating conductor and electrons losing kinetic energy themselves

Was the explanation that they collide with ions not good enough?
 
  • #6
hilbert2
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In the relatively simple Drude model, the conduction electrons are treated as classical particles that can collide with the atomic cores. If the electrons are accelerated by an electrical field, the collisions increase the vibration of the atoms and cause heating. See http://en.wikipedia.org/wiki/Drude_model .

In a quantum mechanical treatment, electrons are not seen as classical particles and we talk about electron-phonon scattering as the source of electrical resistivity and heating.
 
  • #7
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Thank you guys. I wonder if it seems possible to explain QM situation simply?

There is a challenge
 

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