Peter
Dec14-04, 10:18 AM
<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no, location=no,scrollbars=yes,resizable=yes,status=no ,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>\nHello:\n\nI have a couple of questions on electron transport (in metals):\n\n1. Consider a metal wire connecting the two terminals of a power\nsource. What exactly happens? Is it correct to say that electrons\nbehave as particles and flow in the wire at the drift velocity (v)\namidst random thermal motion to produce the required current? [I =\nn*(-e)*v*A; I: current, n: free electron density, e: electronic charge,\nA: cross section of the wire]\n\n2. What exactly "makes" the electrons to flow? If it is the electric\nfield, what causes the electric field? Would it be correct to say that\nthe electrons at one end of the terminal have a higher ionization\npotential compared to the other end and that the electric field is just\na convenient way to express this difference in the "potential energy"?\n\n3. Don\'t electrons themselves, being charged particles, create an\nelectric field? Shouldn\'t the electrons so rearrange themselves to\ncounteract this external field and so stop the flow of current?\n\n4. Does one terminal keep supplying electrons steadily into the wire to\nprevent the stagnation of current as mention in Q3 above? If so, is\nthere a concentration gradient of electrons along the wire from the\nsource terminal to the drain terminal?\n\n5. What happens if there is a bend in the wire? Shouldn\'t that affect\nthe field created by the electrons? Shouldn\'t it affect the current\nflow? In other words will the following two structures have the same\nresistance (assume they have the same total length):\n\n\nS________________D\n\n\nS____/\\______D\n\n\nS: Source , D: Drain\n\nWhat, in particular, if the wire dimensions are comparable to the\nelectron mean free path?\n\n6. I know that the energy of the electron in a metal (or in any\nperiodic lattice) is related to its momentum through the band\nstructure. How does this actually affect the particle picture of\nelectron flow in a metallic wire?\n\n7. I know that, for low electric fields, wave packets of electrons in a\nband can be considered to behave as particles obeying Newtons laws to\ndescribe the time dependence of their (crystal) momentum. Please\ncorrect me if my understanding is incorrect/incomplete.\n\nClear, detailed, convincing, patient answers would be most sincerely\nappreciated.\n\nPeter\n\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form"> View this Usenet post in original ASCII form </a></div><P></jabberwocky>Hello:
I have a couple of questions on electron transport (in metals):
1. Consider a metal wire connecting the two terminals of a power
source. What exactly happens? Is it correct to say that electrons
behave as particles and flow in the wire at the drift velocity (v)
amidst random thermal motion to produce the required current? [I =n*(-e)*v*A; I: current, n: free electron density, e: electronic charge,
A: cross section of the wire]
2. What exactly "makes" the electrons to flow? If it is the electric
field, what causes the electric field? Would it be correct to say that
the electrons at one end of the terminal have a higher ionization
potential compared to the other end and that the electric field is just
a convenient way to express this difference in the "potential energy"?
3. Don't electrons themselves, being charged particles, create an
electric field? Shouldn't the electrons so rearrange themselves to
counteract this external field and so stop the flow of current?
4. Does one terminal keep supplying electrons steadily into the wire to
prevent the stagnation of current as mention in Q3 above? If so, is
there a concentration gradient of electrons along the wire from the
source terminal to the drain terminal?
5. What happens if there is a bend in the wire? Shouldn't that affect
the field created by the electrons? Shouldn't it affect the current
flow? In other words will the following two structures have the same
resistance (assume they have the same total length):
S_{_______________D}
S_{___}/\__{____D}
S: Source , D: Drain
What, in particular, if the wire dimensions are comparable to the
electron mean free path?
6. I know that the energy of the electron in a metal (or in any
periodic lattice) is related to its momentum through the band
structure. How does this actually affect the particle picture of
electron flow in a metallic wire?
7. I know that, for low electric fields, wave packets of electrons in a
band can be considered to behave as particles obeying Newtons laws to
describe the time dependence of their (crystal) momentum. Please
correct me if my understanding is incorrect/incomplete.
Clear, detailed, convincing, patient answers would be most sincerely
appreciated.
Peter
I have a couple of questions on electron transport (in metals):
1. Consider a metal wire connecting the two terminals of a power
source. What exactly happens? Is it correct to say that electrons
behave as particles and flow in the wire at the drift velocity (v)
amidst random thermal motion to produce the required current? [I =n*(-e)*v*A; I: current, n: free electron density, e: electronic charge,
A: cross section of the wire]
2. What exactly "makes" the electrons to flow? If it is the electric
field, what causes the electric field? Would it be correct to say that
the electrons at one end of the terminal have a higher ionization
potential compared to the other end and that the electric field is just
a convenient way to express this difference in the "potential energy"?
3. Don't electrons themselves, being charged particles, create an
electric field? Shouldn't the electrons so rearrange themselves to
counteract this external field and so stop the flow of current?
4. Does one terminal keep supplying electrons steadily into the wire to
prevent the stagnation of current as mention in Q3 above? If so, is
there a concentration gradient of electrons along the wire from the
source terminal to the drain terminal?
5. What happens if there is a bend in the wire? Shouldn't that affect
the field created by the electrons? Shouldn't it affect the current
flow? In other words will the following two structures have the same
resistance (assume they have the same total length):
S_{_______________D}
S_{___}/\__{____D}
S: Source , D: Drain
What, in particular, if the wire dimensions are comparable to the
electron mean free path?
6. I know that the energy of the electron in a metal (or in any
periodic lattice) is related to its momentum through the band
structure. How does this actually affect the particle picture of
electron flow in a metallic wire?
7. I know that, for low electric fields, wave packets of electrons in a
band can be considered to behave as particles obeying Newtons laws to
describe the time dependence of their (crystal) momentum. Please
correct me if my understanding is incorrect/incomplete.
Clear, detailed, convincing, patient answers would be most sincerely
appreciated.
Peter