Elementary musings

[gareth]

When I started out, it seemed that the phenomenom of resistance was
intuitive, based on direct experience of electric fires and lamps, not
forgetting the water pressure model, but those of inductance and
capacitance were mysterious especially in the AC model where the PI/2
phase shift came in, eg, how could current be delivered when the voltage
is zero, etc. (No, I'm not asking that question today)

Later on, based on the storage of energy within the devices, capacitance
and inductance were easy, but what actually happens in resistance?

Consider the model of conduction where energised electrons can only move
from atom to atom via unoccupied orbital energy levels, then what
happens in a resistance when the electron gives heat energy to the
material? In dropping down an energy level, some form of photon must
be given off, but how is that absorbed by the whole atom to increase the
atom's vibration? (Yes, I am asking that question today, despite
being completely au fait with series, parallel, Norton and Thevenin, etc)

Also, why is an electron in motion in a resistance more likely to
release its energy than an electron in motion in, say, copper?

I do not have all the answers and googling sends me off to advanced
physics (Schroedinger waves, quarks, etc) when what I seek is an
explanation that is elevant to engineering rather then to physics,
accepting that at each level of electrical engineering education there
are models presented that are gross simplifications but gaining in
sophistication as one's knowledge develops.

[AndyW]

On 12/02/2017 18:53, gareth wrote:

> I do not have all the answers and googling sends me off to advanced
> physics (Schroedinger waves, quarks, etc) when what I seek is an
> explanation that is elevant to engineering rather then to physics,
> accepting that at each level of electrical engineering education there
> are models presented that are gross simplifications but gaining in
> sophistication as one's knowledge develops.

The problem is that modern conduction theory uses quantum effects and so
there comes a point when, if you don't want to deal in the weeds of
quantum effects, then you just have to stop digging.
Charge Density Wave explains how charge moves in a conductor (but
electrons do not necessarily move), it is in the realms of quantum
effects and I barely follow the abstracts. If you need more than
standard quantum physics in relation to junction scale electronics then
I will be of no use.

The real-life model is a hosepipe full of marbles, you pop a marble in
one end and a marbles pops out the other end. One marble's worth of
information but a different marble.

As for what is resistance in this context, basically nobody knows, there
are competing theories, the popular one seems to be noise effects
(usually thermal) in the conductor causing ripples that degrade the
conduction wave in the same way that a ripple on water can be disrupted
by small wavelets, splashes etc. There is a mechanical explanation of
resistance that impurities in the lattice impede the ripple of the
signal or simply leave a hole for the electron to move into and so
absorb some energy from the wave (a gap between marbles if you like)

Andy

[Brian Reay]

A 'simple' model relies on thermal excitation.

Taking your marble in a hose pipe but expanding it to a lot of marbles
in a larger pipe. You stuff in some at one end, as many pop out, but
some energy is lost in the process, some energy having been transferred
to heat as the marbles move.

At the atom or electron scale, some energy 'raises' electrons (no all
'risings and lowering' are photon related) to a higher energy state-
thermal agitation. The rest we see as electron 'drift', more of an
ability to 'bump' the next chap than a flow. In good conductors, less
goes into 'local' agitation (heating) and 'drift' is 'easier'.



--

Suspect someone is claiming a benefit under false pretences? Incapacity
Benefit or Personal Independence Payment when they don't need it? They
are depriving those in real need!

https://www.gov.uk/report-benefit-fraud

[gareth]

On 13/02/2017 08:17, AndyW wrote:

Thanks for a full analysis, for it certainly seems that when you start
off knowing nothing then resistance is easy to understand but when you know
a little more then resistance is well nigh impossible (for an engineer
but possibly not a scientist) to understand.

[gareth]

On 13/02/2017 08:58, Brian Reay wrote:
> At the atom or electron scale, some energy 'raises' electrons (no all
> 'risings and lowering' are photon related) to a higher energy state-
> thermal agitation.

Yes, of course, I'd forgotten about thermal excitation as it is
described for semiconductor theory, thank-you.

However, thermal energy is a form of electromagnetic energy, so it
could well be photon related except that it is never described as such.

Brian, well done, keep up the practice of contributing positive
responses and then perhaps you won't feel so much the need to sneer
and put down others?

[AndyW]

On 13/02/2017 20:03, gareth wrote:

> Thanks for a full analysis, for it certainly seems that when you start
> off knowing nothing then resistance is easy to understand but when you know
> a little more then resistance is well nigh impossible (for an engineer
> but possibly not a scientist) to understand.

I did a physics degree and at the end of it what I learned was basically
that nobody knows.
The leading edge of really clever people just don't know but are trying
to find out, everyone else digs down through different strata of 'lies
to children' of increasing complexity until they reach an explanation
that they are comfortable with and just stop digging.
When it come to what matter is made from I was happy to dig down past
atoms, into protons and electrons and even down to quarks and gluons but
I simply cannot begin understand wave packet and string theory.
I'm happy with the billiard ball lie about protons and electrons and
just about able to deal with quarks and lepton with sufficient warning
and a good run up.
Electromagnetic waves I think of as the classical model. I struggle with
the modern explanations, too much hard thinking.

Andy

[108at144 A new UK AMATEUR RADIO CALL SIGN]

nnnbb. ccccvv