Re: emf, potential, voltage

[brian whatcott <inet@INTELLISYS.NET>]

I will simply offer a reductio model:
from the universe of two terminal devices, I will choose
the thermionic or high field diode.
 The same numbers of electrons leave the cathode
as hit the anode in a given time interval, but in transit
 they accelerate.
 Their kinetic energy is surrendered at the anode.

This example illustrates that though
x - # of carriers per unit time may be fixed,
n - # of carriers per unit volume may vary with
velocity.
If one selects resistors from the universe of two terminal
devices, then acceleration is countered by impact, and
a mean charge velocity proportional to the magnitude of the
electric field results, which is in practical cases
surprisingly slow.
 When semiconductor designers were finally goaded into
considering the acceleration offered in thermionic devices
compared with the rather low speeds in semiconductors,
they responded with "high electron mobility" devices.

Brian Whatcott

At 00:42 3/13/01 -0500, you wrote:
> If n = # of carriers per unit volume,
> q = charge per carrier,
> A=cross sectional area of a cylindrical wire,
> v= carrier speed,
>
> Then the current in this wire is I = nqAv
>
> It is easy to arrange n,q and A to be the same in both resistor leads.
> Then if I measure I_in = I_out, this model says v_in = v_out.
>
> Some basic assumptions are of course involved, but they are not outlandish.
>
> Bob Sciamanda (W3NLV)
> Physics, Edinboro Univ of PA (em)
> trebor@velocity.net
> www.velocity.net/~trebor
> ----- Original Message -----
> From: "brian whatcott" <inet@INTELLISYS.NET>
> To: <PHYS-L@lists.nau.edu>
> Sent: Tuesday, March 13, 2001 12:03 AM
> Subject: Re: emf, potential, voltage
>
>
> > At 23:20 3/12/01 -0500, Bob Sciamanda wrote:
> > > Consider any two terminal device with a current of I amperes flowing
> > > through it down a potential hill of V volts.  That means there is an
> > > electrostatic field in the device which is giving energy to the charge
> > > carriers as they pass through the device, down the potential hill.  If
> this
> > > were the whole story, the carriers would emerge from the device with
> > > increased kinetic energy, and the current out of the device would exceed
> the
> > > current into the device.
> > /snip/
> > > Bob Sciamanda (W3NLV)
> > > Physics, Edinboro Univ of PA (em)
> > > trebor@velocity.net
> > > www.velocity.net/~trebor
> >
> >
> > Consider a stream of vehicles entering an on ramp at 10 miles per hour.
> > Let us call the current or 'traffic flow rate' x vehicles per hour.
> >
> > Before they  merge on the throughway, vehicles match speed with the
> > throughway traffic travelling at 30 miles per hour.
> >  What is their flow rate at this time?
> >
> > (They have gained kinetic energy, but the on ramp exit current has
> > *not* increased, the traffic flow rate is *still* x vehicles per hour)
> >
> >
> >
> > brian whatcott <inet@intellisys.net>  Altus OK
> >                 Eureka!
brian whatcott <inet@intellisys.net>  Altus OK
                Eureka!