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In article <q91st99pdum1bb9k4p721aitlmg8q4bkle@4ax.com>, fake@ddress.no
says...
On Sat, 2 Aug 2014 09:59:13 -0400, "Maynard A. Philbrook Jr."
jamie_ka1lpa@charter.net> wrote:
I am going to give you the water analogy, which I think is as accurate
as it gets.
Your water flow analogy is completely wrong.
Voltage represents pressure.
Current represents quantity of water per time.
Resistance represents the flow restriction.
What ever you say... I've gone by that for the last 45 years
and it has not failed me yet. AS I have also past that on
to many and it has worked for them, too!
Think as you may, it works for me.
On 8/2/2014 7:58 AM, Ian Malcolm wrote:
Robert Roland <fake@ddress.no> wrote in
news:jfbpt99105amnmveclieglqlp57mjiomph@4ax.com:
On Fri, 01 Aug 2014 22:38:37 +0200, Cursitor Doom
cd@spamfreezone.net> wrote:
Is the following statement beyond dispute: "You have to induce a
voltage before you will get a current flowing."
In a purely resistive circuit, the current is driven by the voltage.
Sometimes, it's easier to think of current as water flow. If there is
no pressure (voltage) difference, then the water will not move
(current).
ISTR it's not quite that simple and in some instances the current
comes first and a potential difference arises from that.
In an inductive circuit, changing the current will create a voltage.
Look at the water analogy again. The water has mass. The mass
represents the inductance. Once the water is moving through a pipe, it
will continue to move even though there is no pressure difference. If
you force it to stop, a pressure will occur. The more abruptly the
flow is stopped, the higher the pressure will be.
In short: You can not get a current going without voltage, but once it
is going, it will continue to flow if there is inductance.
If you are familiar with Newtonian physics, you can use a similar
analogy where voltage is force and inductance is mass. (Also,
resistance is friction and capacitance is a spring).
You need force to get the mass moving, but once it is moving, it will
create a force if you try to stop it.
Its not simple at all if you dont exclude the special case of
superconductivity.
Take a ring made of a superconductor. Start above its transition
temperature and place between the poles of a strong magnet parallel to
the pole piece faces. Chill the ring below the transition temperature
and it will trap all the flux through the ring. Remove it from between
the pole pieces and a permanent current is induced in the ring sufficient
to maintain the trapped flux which will persist till the ring is warmed
above the transition temperature or is broken.
As it is a superconductor, the voltage difference between any two points
on its surface is always zero.
At DC, that is. Superconductors also exhibit an astounding amount of
inductance from the inertia of the electron pairs.
Cheers
Phil Hobbs
On Sun, 3 Aug 2014 09:51:36 -0400, "Maynard A. Philbrook Jr."
jamie_ka1lpa@charter.net> wrote:
In article <q91st99pdum1bb9k4p721aitlmg8q4bkle@4ax.com>, fake@ddress.no
says...
On Sat, 2 Aug 2014 09:59:13 -0400, "Maynard A. Philbrook Jr."
jamie_ka1lpa@charter.net> wrote:
I am going to give you the water analogy, which I think is as accurate
as it gets.
Your water flow analogy is completely wrong.
Voltage represents pressure.
Current represents quantity of water per time.
Resistance represents the flow restriction.
What ever you say... I've gone by that for the last 45 years
and it has not failed me yet. AS I have also past that on
to many and it has worked for them, too!
Think as you may, it works for me.
---
Have you ever wondered why water has to go **through** a flowmeter
but only **touch** a pressure meter?
On Sat, 2 Aug 2014 09:59:13 -0400, "Maynard A. Philbrook Jr."
jamie_ka1lpa@charter.net> wrote:
I am going to give you the water analogy, which I think is as accurate
as it gets.
You are standing beside a small stream and the water is moving lets say
1 ft/sec. The speed of which that is moving is the VOLTAGE.
---
Well, first of all, if you're talking about the flow of water down a
stream, isn't the flow referred to as a 'current'? , as in: "Be
careful crossing that stream, it has a dangerously fast current."
Knowing that, it's not much of a leap to realize that if you want to
use the water analogy and you liken the water molecules to
electrons, then since the stream's current will indicate how many
water molecules move past a given point in a certain time, electric
current will indicate how many electrons move past a given point in
a certain time.
In the electric world, the unit of current is the ampere, and one
ampere is 6.241×10e18 electrons moving past a fixed point in one
second. Twice that many moving past a fixed point in one second
would be two amperes, and so on.
6.241×10e18 electrons is called a 'coulomb' and, for the purpose of
the analogy, can be likened to, say, a gallon's worth of water
molecules.
Now we can equate flow in both systems by saying that a flow of one
coulomb per second through a wire is like a flow of one gallon per
second through a pipe.
So now let's double the pressure in the hose and what'll happen?
The flow will increase to two gallons per minute, and if we double
the voltage on the wire what'll happen?
Bingo! The current will increase to two coulombs per second, which
is two amperes.
So now we have pressure analogous to voltage and flow analogous to
current.
All that's left now is resistance, and if we say that if, at a given
pressure, we can pump one gallon per second through a pipe with a
given length and cross-sectional area, we can also say that if we
increase the length or decrease the cross sectional area by a factor
of two, the flow will drop to one half-gallon per second.
Likewise, if we have a length of wire with a given voltage across it
and a current of one ampere through it and we increase the length of
the wire or decrease the cross sectional area by a factor of two,
the current will drop to one half of an ampere.
In both cases the resistance was increased, resulting in a decrease
of flow, so there you have it:
Voltage is analogous to pressure,
Current is analogous to flow, and
Resistance is analogous to resistance.
In article <1knst9lmv4me86tgn2me1955biui51ba2a@4ax.com>,
jfields@austininstruments.com says...
On Sun, 3 Aug 2014 09:51:36 -0400, "Maynard A. Philbrook Jr."
jamie_ka1lpa@charter.net> wrote:
In article <q91st99pdum1bb9k4p721aitlmg8q4bkle@4ax.com>, fake@ddress.no
says...
On Sat, 2 Aug 2014 09:59:13 -0400, "Maynard A. Philbrook Jr."
jamie_ka1lpa@charter.net> wrote:
I am going to give you the water analogy, which I think is as accurate
as it gets.
Your water flow analogy is completely wrong.
Voltage represents pressure.
Current represents quantity of water per time.
Resistance represents the flow restriction.
What ever you say... I've gone by that for the last 45 years
and it has not failed me yet. AS I have also past that on
to many and it has worked for them, too!
Think as you may, it works for me.
---
Have you ever wondered why water has to go **through** a flowmeter
but only **touch** a pressure meter?
I will ignore you like most others do with some common sence.
Jamie
Voltage is analogous to pressure,
Current is analogous to flow, and
Resistance is analogous to resistance.
Nice clear explanation as usual, Mr. Fields. It doesn't make sense any
other way.
There is one aspect of the water analogy that doesn't equate, though,
and that is *speed* of flow (as distinct from volume) - it doesn't
apply with electrons.
On Sunday, August 3, 2014 10:16:37 AM UTC-7, John Larkin wrote:
On Sun, 03 Aug 2014 08:54:51 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:
As it is a superconductor, the voltage difference between any two points
on its surface is always zero.
At DC, that is. Superconductors also exhibit an astounding amount of
inductance from the inertia of the electron pairs.
Inductance is an inertia-like effect, but the real mass and charge of electron
pairs is unimportant; it's the magnetic field that causes inductance.
Is the inductance of a superconducting ring or coil very high?
Same as that geometry would have in regular-old-wire conductors; the
real difference is in the L/R ratio. That inductive decay time is REAL long.
I really want surface-mount room-temp superconducting inductors!
Unless your other elements are superconducting, too, you lose the L/R
benefit... what's left, is small size for high current, with no self-heating
limit.
On Sunday, August 3, 2014 10:16:37 AM UTC-7, John Larkin wrote:
On Sun, 03 Aug 2014 08:54:51 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:
As it is a superconductor, the voltage difference between any two points
on its surface is always zero.
At DC, that is. Superconductors also exhibit an astounding amount of
inductance from the inertia of the electron pairs.
Inductance is an inertia-like effect, but the real mass and charge of electron
pairs is unimportant; it's the magnetic field that causes inductance.
Is the inductance of a superconducting ring or coil very high?
Same as that geometry would have in regular-old-wire conductors; the
real difference is in the L/R ratio. That inductive decay time is REAL long.
I really want surface-mount room-temp superconducting inductors!
Unless your other elements are superconducting, too, you lose the L/R
benefit... what's left, is small size for high current, with no self-heating
limit.
In article <1knst9lmv4me86tgn2me1955biui51ba2a@4ax.com>,
jfields@austininstruments.com says...
On Sun, 3 Aug 2014 09:51:36 -0400, "Maynard A. Philbrook Jr."
jamie_ka1lpa@charter.net> wrote:
In article <q91st99pdum1bb9k4p721aitlmg8q4bkle@4ax.com>, fake@ddress.no
says...
On Sat, 2 Aug 2014 09:59:13 -0400, "Maynard A. Philbrook Jr."
jamie_ka1lpa@charter.net> wrote:
I am going to give you the water analogy, which I think is as accurate
as it gets.
Your water flow analogy is completely wrong.
Voltage represents pressure.
Current represents quantity of water per time.
Resistance represents the flow restriction.
What ever you say... I've gone by that for the last 45 years
and it has not failed me yet. AS I have also past that on
to many and it has worked for them, too!
Think as you may, it works for me.
---
Have you ever wondered why water has to go **through** a flowmeter
but only **touch** a pressure meter?
I will ignore you like most others do with some common sence.
Jamie
On Sun, 03 Aug 2014 08:54:51 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:
Is the inductance of a superconducting ring or coil very high?
Depends. Kinetic inductance is linear in the wire length, because itsOn 2014-08-03, John Larkin <jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:
On Sun, 03 Aug 2014 08:54:51 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:
Is the inductance of a superconducting ring or coil very high?
about the same as a wire ring or coil of the same dimensions,
On Sunday, August 3, 2014 4:17:17 PM UTC-7, John Larkin wrote:
I can get good small Hi-Q capacitors, but the inductors are terrible.
So, it takes a bit of work with an amplifier and some positive feedback to
concoct a negative resistance in series with the resistive inductor...
Absolutely pathetic..
Cool, thanks.On 8/3/2014 4:01 PM, whit3rd wrote:
On Sunday, August 3, 2014 10:16:37 AM UTC-7, John Larkin wrote:
On Sun, 03 Aug 2014 08:54:51 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:
As it is a superconductor, the voltage difference between any two points
on its surface is always zero.
At DC, that is. Superconductors also exhibit an astounding amount of
inductance from the inertia of the electron pairs.
Inductance is an inertia-like effect, but the real mass and charge of electron
pairs is unimportant; it's the magnetic field that causes inductance.
Is the inductance of a superconducting ring or coil very high?
Same as that geometry would have in regular-old-wire conductors; the
real difference is in the L/R ratio. That inductive decay time is REAL long.
I really want surface-mount room-temp superconducting inductors!
Unless your other elements are superconducting, too, you lose the L/R
benefit... what's left, is small size for high current, with no self-heating
limit.
Google for "kinetic inductiance".
Cheers
Phil Hobbs
--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics
160 North State Road #203
Briarcliff Manor NY 10510
hobbs at electrooptical dot net
http://electrooptical.net
Hi all,
Is the following statement beyond dispute: "You have to induce a
voltage before you will get a current flowing."
ISTR it's not quite that simple and in some instances the current
comes first and a potential difference arises from that. Can any
knowledgeable fellow here elaborate?
ISTR it's not quite that simple and in some instances the current
comes first and a potential difference arises from that. Can any
knowledgeable fellow here elaborate?
ISTR it's not quite that simple and in some instances the current
comes first and a potential difference arises from that. Can any
knowledgeable fellow here elaborate?