Turn Your Power Supply into an Ohmmeter - It's Free!

[Clifton T. Sharp Jr.]

Bob Masta wrote:

How do the Greeks pronounce "gigas"?

My limited experience and very limited study would say all g's in Greek
are hard g's. They produce a soft-g sound with "dz"; this part I'm
pretty sure of, as I worked a few years for a "Dzimmy" Brillakis.

--
The function of an asshole is to emit quantities of crap. Spammers do
a very good job of that. However, I do object to my inbox being a
spammer's toilet bowl. -- Walter Dnes

 

[Watson A.Name - 'Watt Sun]

In article <3f1a8f6e.1627749@news.itd.umich.edu>, no_spam@aol.com
mentioned...

On Sun, 20 Jul 2003 08:50:43 +1000, Franc Zabkar
fzabkar@optussnet.com.au> wrote:


I would think the most sensible pronunciation would be "giga" as this
prefix is derived from the Greek word, "gigas", meaning "giant".

How do the Greeks pronounce "gigas"? The "jig-a" pronounciation
for giga seems to be in more-or-less in keeping with "gigantic".

Are there any hard-"g" English words with the "giant" meaning?

Not that anything is going to change common usage! ;-)

The NIST page doesn't show the pronunciation. Here's the URL:
http://physics.nist.gov/cuu/Units/prefixes.html

But see here: http://wombat.doc.ic.ac.uk/foldoc/foldoc.cgi?giga-
and here:
http://www.m-w.com/cgi-bin/dictionary?book=Dictionary&va=giga-
Generally speaking, the first listing in the dictionary is the
preferred pronunciation.

And the following URL talks ad nauseum about the pronunciation, but
all that is moot since the reference publications from NBS (now NIST)
(which are presumably derived from the SI international stds), and
such pubs as the U.S. Navy and ASME give the prounciation as jiga.
http://www.lns.cornell.edu/spr/2001-12/msg0037637.html

Bob Masta
tech(AT)daqarta(DOT)com

--
@@F@r@o@m@@O@r@a@n@g@e@@C@o@u@n@t@y@,@@C@a@l@,@@w@h@e@r@e@@
###Got a Question about ELECTRONICS? Check HERE First:###
http://users.pandora.be/educypedia/electronics/databank.htm
My email address is whitelisted. *All* email sent to it
goes directly to the trash unless you add NOSPAM in the
Subject: line with other stuff. alondra101 <at> hotmail.com
Don't be ripped off by the big book dealers. Go to the URL
that will give you a choice and save you money(up to half).
http://www.everybookstore.com You'll be glad you did!
Just when you thought you had all this figured out, the gov't
changed it: http://physics.nist.gov/cuu/Units/binary.html
@@t@h@e@@a@f@f@l@u@e@n@t@@m@e@e@t@@t@h@e@@E@f@f@l@u@e@n@t@@

 

[Tim Williams]

"Ratch" <Watchit@Comcast.net> wrote in message
news:%RxSa.92479$GL4.26156@rwcrnsc53...

Wait a minute, if L&M say that Ohm's law is V=IR (which it is not),
and
materials that obey Ohm's law are "ohmic", then by L&M's definition, all
materials are ohmic because the resistance formula V=IR is always correct
for all materials. How is a material defined as "nonohmic"? Ratch

Ohm's law. Sounds to me like it applies when R represents an ohmic
material.
*duh*

And it still applies. Let's say we forward bias a diode. So, we put 20mA
on it and measure .7V. V=IR = .7 = .02R, divide by .02 and we find the
diode is 35 ohms. Of course, since it's a nearly constant voltage whatever
the current flowing, the resistance drops as current rises, making it a
rather nonohmic component, and it's a more or less pointless calculation.
But it still applies: given the current doesn't change from those 20mA,
it could be replaced by a 35 ohm resistor and the same voltage drop is
produced.

Tim

 

[Tim Williams]

"Costas Vlachos" <c-X-vlachos@hot-X-mail.com> wrote in message
news:bfeu6l$sf9$1@hercules.btinternet.com...

Do people use the "jig-a" way? Never heard of it.

No? Jigawatts? ;-)

Tim

--
In the immortal words of Ned Flanders: "No foot longs!"
Website @ http://webpages.charter.net/dawill/tmoranwms

 

[Chuck Harris]

Hi Ratch,

Ratch wrote:

Wait a minute, if L&M say that Ohm's law is V=IR (which it is not), and
materials that obey Ohm's law are "ohmic", then by L&M's definition, all
materials are ohmic because the resistance formula V=IR is always correct
for all materials. How is a material defined as "nonohmic"? Ratch

No, not quite, ohmic materials by definition have a current density that
is *proportional* to the electric field. Or in other words have a rho
that is a simple constant.

j = E/rho, or E = j * rho

If you have a material where rho is not a simple constant, but rather is
a function of current density, you have a non-ohmic material.

This applies to either way of writing Ohm's law, because rho and R are
proportional to each other.

So, as a result, if R is some function of I, the material is non ohmic.

There is no inconsistency.

-Chuck

 

[Franc Zabkar]

On Sun, 20 Jul 2003 12:21:18 -0700, Watson A.Name - 'Watt Sun'
<alondra101@hotmail.com> put finger to keyboard and composed:

In article <3f1a8f6e.1627749@news.itd.umich.edu>, no_spam@aol.com
mentioned...
On Sun, 20 Jul 2003 08:50:43 +1000, Franc Zabkar
fzabkar@optussnet.com.au> wrote:


I would think the most sensible pronunciation would be "giga" as this
prefix is derived from the Greek word, "gigas", meaning "giant".

How do the Greeks pronounce "gigas"? The "jig-a" pronounciation
for giga seems to be in more-or-less in keeping with "gigantic".

Are there any hard-"g" English words with the "giant" meaning?

Not that anything is going to change common usage! ;-)


The NIST page doesn't show the pronunciation. Here's the URL:
http://physics.nist.gov/cuu/Units/prefixes.html

But see here: http://wombat.doc.ic.ac.uk/foldoc/foldoc.cgi?giga-
and here:
http://www.m-w.com/cgi-bin/dictionary?book=Dictionary&va=giga-
Generally speaking, the first listing in the dictionary is the
preferred pronunciation.

My Concise Oxford dictionary lists both pronunciations for "giga" as
being acceptable, although here in Australia absolutely nobody uses
the "jiga" form. My dictionary also lists both pronunciations for
kilometre, although the ki-lometter version is "disputed", for obvious
reasons.

And the following URL talks ad nauseum about the pronunciation, but
all that is moot since the reference publications from NBS (now NIST)
(which are presumably derived from the SI international stds), and
such pubs as the U.S. Navy and ASME give the prounciation as jiga.
http://www.lns.cornell.edu/spr/2001-12/msg0037637.html

I'm not sure that one could consider any US based metric reference to
be authoritative. Apart from Liberia and Myanmar (Burma), the USA is
the only other country that retains the old Imperial system of weights
and measures. I reckon you guys ought to pronounce *our* system the
way *we* do.

Bob Masta
tech(AT)daqarta(DOT)com

- Franc Zabkar
--
Please remove one 's' from my address when replying by email.

 

[Costas Vlachos]

"Bob Masta" <no_spam@aol.com> wrote in message
news:3f1a8f6e.1627749@news.itd.umich.edu...

On Sun, 20 Jul 2003 08:50:43 +1000, Franc Zabkar
fzabkar@optussnet.com.au> wrote:


I would think the most sensible pronunciation would be "giga" as this
prefix is derived from the Greek word, "gigas", meaning "giant".

How do the Greeks pronounce "gigas"? The "jig-a" pronounciation
for giga seems to be in more-or-less in keeping with "gigantic".

The Greek pronunciation for "giga" uses hard "g" sounds, just like "Greek".
Not like "gigantic". Do people use the "jig-a" way? Never heard of it.

Costas

 

[Ratch]

"Tim Williams" <tmoranwms@charter.net> wrote in message
news:vhm06t95ft6t24@corp.supernews.com...

"Ratch" <Watchit@Comcast.net> wrote in message
news:%RxSa.92479$GL4.26156@rwcrnsc53...
Wait a minute, if L&M say that Ohm's law is V=IR (which it is not),
and
materials that obey Ohm's law are "ohmic", then by L&M's definition, all
materials are ohmic because the resistance formula V=IR is always
correct
for all materials. How is a material defined as "nonohmic"? Ratch

Ohm's law. Sounds to me like it applies when R represents an ohmic
material.
*duh*

The above statement does not answer my question.

And it still applies. Let's say we forward bias a diode. So, we put 20mA
on it and measure .7V. V=IR = .7 = .02R, divide by .02 and we find the
diode is 35 ohms. Of course, since it's a nearly constant voltage
whatever
the current flowing, the resistance drops as current rises, making it a
rather nonohmic component, and it's a more or less pointless calculation.
But it still applies: given the current doesn't change from those 20mA,
it could be replaced by a 35 ohm resistor and the same voltage drop is
produced.

All you have shown above is that the resistance formula V=IR is
correct. L&M says V=IR is Ohm's law (which it is not), and if all materials
obey what L&M calls Ohm's law (which they do), then the material is ohmic.
Therefore by that reason, ALL materials are ohmic (which they are not). Do
you see the inconsistency of what L&M is saying? Ratch

 

[Ratch]

"Chuck Harris" <cfharris@erols.com> wrote in message
news:bfevp4$its$1@bob.news.rcn.net...

Hi Ratch,

Ratch wrote:

Wait a minute, if L&M say that Ohm's law is V=IR (which it is not),
and
materials that obey Ohm's law are "ohmic", then by L&M's definition, all
materials are ohmic because the resistance formula V=IR is always
correct
for all materials. How is a material defined as "nonohmic"? Ratch

No, not quite, ohmic materials by definition have a current density that
is *proportional* to the electric field. Or in other words have a rho
that is a simple constant.

j = E/rho, or E = j * rho

If you have a material where rho is not a simple constant, but rather is
a function of current density, you have a non-ohmic material.

I agree with what you said above.

This applies to either way of writing Ohm's law, because rho and R are
proportional to each other.

Yes, rho and R are proportional to each other, but that does not answer
the question I asked before (see the first paragraph above). How does L&M
define something as nonohmic when according to what they say, everything is
ohmic because it follows V=IR (which they say is Ohm's law).

So, as a result, if R is some function of I, the material is non ohmic.

I agree with that, but according to what you said about what L&M
writes, that never happens because all materials follow V=IR. Does L&M
mention
nonohmic materials? Ohm's law cannot be both V=IR and constant resistance
as current varies. Which one does L&M say it is? Ratch

There is no inconsistency.

Yes, according to what L&M says there is. Ratch

 

[Chuck Harris]

Hi Ratch,

No one has said all materials are ohmic.

What I understand L&M to be saying is that if j is proportional to E,
the material is ohmic. Proportionality requires j and E to be
related by a CONSTANT (constant relative to j and E, that is).

If rho is a constant, the material is ohmic. If rho is not constant,
the material is not ohmic.

In quoting L&M, I left off the first paragraph where they discuss rho
being constant, to wit:


[4. OHM's LAW

If there is no electric field in a conductor, there is also no
electric current; the mean velocity (v) of the charge carriers
(electrons) vanishes. In many, although by no means all, materials the
current density is proportional to the electric field:

j = (1/rho) * E (9-16)

The quantity rho is called the resistivity of the material; its inverse
1/rho is usually called the conductivity. It is a property of the
material; in addition, it will vary with the temperature of the
conductor.

Eq. (9-16) describes the current density in terms of the electric
field at a point in a conductor (Fig. 9-11). It is called Ohm's law.
materials that obey Ohm's law are usually called ohmic conductors. This
relation enables us to calculate the current flowing through a wire of
length L which is connected to two terminals - points between which
there is a potential difference V....]



L&M could have said a bit more about what they meant about a material
not following Ohm's law; how they meant that a material that has a non
constant rho is non ohmic. However, I caught the meaning the first time
I read it, so it cannot have been too badly worded.

The trip from (9-16) to: V = RI is just a straight forward
rearrangement, and substitution. It still states the same thing as
(9-16). A material is non ohmic if R is not a constant.

-Chuck

Ratch wrote:>

Yes, rho and R are proportional to each other, but that does not answer
the question I asked before (see the first paragraph above). How does L&M
define something as nonohmic when according to what they say, everything is
ohmic because it follows V=IR (which they say is Ohm's law).


So, as a result, if R is some function of I, the material is non ohmic.


I agree with that, but according to what you said about what L&M
writes, that never happens because all materials follow V=IR. Does L&M
mention
nonohmic materials? Ohm's law cannot be both V=IR and constant resistance
as current varies. Which one does L&M say it is? Ratch


There is no inconsistency.


Yes, according to what L&M says there is. Ratch

 

[Ratch]

"Chuck Harris" <cfharris@erols.com> wrote in message
news:bfffcs$r6t$1@bob.news.rcn.net...

Hi Ratch,

No one has said all materials are ohmic.

L&M do not say it directly, but they imply it. See below

What I understand L&M to be saying is that if j is proportional to E,
the material is ohmic. Proportionality requires j and E to be
related by a CONSTANT (constant relative to j and E, that is).

If rho is a constant, the material is ohmic. If rho is not constant,
the material is not ohmic.

What you say above is true, but I don't see L&M saying that. Read
further.

In quoting L&M, I left off the first paragraph where they discuss rho
being constant, to wit:


[4. OHM's LAW

If there is no electric field in a conductor, there is also no
electric current; the mean velocity (v) of the charge carriers
(electrons) vanishes. In many, although by no means all, materials the
current density is proportional to the electric field:

j = (1/rho) * E (9-16)

The quantity rho is called the resistivity of the material; its inverse
1/rho is usually called the conductivity. It is a property of the
material; in addition, it will vary with the temperature of the
conductor.

So far so good. L&M agrees that not all materials have a proportionate
relationship between E and j.

Eq. (9-16) describes the current density in terms of the electric
field at a point in a conductor (Fig. 9-11). It is called Ohm's law.
materials that obey Ohm's law are usually called ohmic conductors. This
relation enables us to calculate the current flowing through a wire of
length L which is connected to two terminals - points between which
there is a potential difference V....]

Now here is where they crash. They first give equation (9-16) and call
it Ohm's law. Then they say that all materials that obey equation (9-16)
are ohmic. Well, all materials obey the resistivity equation (9-16).
Therefore by their reasoning, all materials are ohmic. They go on to say
that Ohm's law can be used to show the relationship between resisitivity,
current density, and electric field. That is certainly true for Equation
(9-16), but that is the resistivity equation and it stands on it own
independent of Ohm's law. The resistivity (9-16) is used to determine
whether a material has the Ohm's law property, but it is not Ohm's law per
se.

L&M could have said a bit more about what they meant about a material
not following Ohm's law; how they meant that a material that has a non
constant rho is non ohmic. However, I caught the meaning the first time
I read it, so it cannot have been too badly worded.

You were primed to understand it because of your exposure to this
discussion.

The trip from (9-16) to: V = RI is just a straight forward
rearrangement, and substitution. It still states the same thing as
(9-16). A material is non ohmic if R is not a constant.

I don't see L&M saying anything that corresponds to the last sentence
above. Again, the resistance equation V=IR can be used to determine if a
material has the Ohm's law property, but V=IR stands on its own and is not
Ohm's law per se. Look at
http://maxwell.byu.edu/~spencerr/websumm122/node50.html again. Ratch

-Chuck

Ratch wrote:
Yes, rho and R are proportional to each other, but that does not
answer
the question I asked before (see the first paragraph above). How does
L&M
define something as nonohmic when according to what they say, everything
is
ohmic because it follows V=IR (which they say is Ohm's law).


So, as a result, if R is some function of I, the material is non ohmic.


I agree with that, but according to what you said about what L&M
writes, that never happens because all materials follow V=IR. Does L&M
mention
nonohmic materials? Ohm's law cannot be both V=IR and constant
resistance
as current varies. Which one does L&M say it is? Ratch


There is no inconsistency.


Yes, according to what L&M says there is. Ratch

 

[Tim Williams]

"Ratch" <Watchit@Comcast.net> wrote in message
news:1PISa.108855$N7.15339@sccrnsc03...

Now here is where they crash. They first give equation (9-16) and
call
it Ohm's law. Then they say that all materials that obey equation (9-16)
are ohmic. Well, all materials obey the resistivity equation (9-16).
Therefore by their reasoning, all materials are ohmic.

Then please, by all means possible, go out and identify all books with
misnomers and incorrect information!!! The world needs you! Why are
you wasting your valuable time on Usenet? Hurry! While there is still
time!!!!

Tim

--
In the immortal words of Ned Flanders: "No foot longs!"
Website @ http://webpages.charter.net/dawill/tmoranwms

 

[Watson A.Name - 'Watt Sun]

In article <vhm09lgbi50673@corp.supernews.com>, tmoranwms@charter.net
mentioned...

"Costas Vlachos" <c-X-vlachos@hot-X-mail.com> wrote in message
news:bfeu6l$sf9$1@hercules.btinternet.com...
Do people use the "jig-a" way? Never heard of it.

No? Jigawatts? ;-)

Jigahurts was the only way I heard Gigahertz pronounced back in the
'60s when I woekrd for a radio eng'g lab. That's not long after the
time when the prefizxes were adopted. Before that, it used to be
micromicrofarads instead of picofarads.

Somehow betwen then and now it got perverted to today's pronunciation.

Tim

--

--
@@F@r@o@m@@O@r@a@n@g@e@@C@o@u@n@t@y@,@@C@a@l@,@@w@h@e@r@e@@
###Got a Question about ELECTRONICS? Check HERE First:###
http://users.pandora.be/educypedia/electronics/databank.htm
My email address is whitelisted. *All* email sent to it
goes directly to the trash unless you add NOSPAM in the
Subject: line with other stuff. alondra101 <at> hotmail.com
Don't be ripped off by the big book dealers. Go to the URL
that will give you a choice and save you money(up to half).
http://www.everybookstore.com You'll be glad you did!
Just when you thought you had all this figured out, the gov't
changed it: http://physics.nist.gov/cuu/Units/binary.html
@@t@h@e@@a@f@f@l@u@e@n@t@@m@e@e@t@@t@h@e@@E@f@f@l@u@e@n@t@@

 

[Asimov]

"Costas Vlachos" wrote to "All" (20 Jul 03 20:31:17)
--- on the topic of "Re: Another twist in the topic (Was Re: Turn Your Power
Supply into an"

CV> From: "Costas Vlachos" <c-X-vlachos@hot-X-mail.com>

How do the Greeks pronounce "gigas"? The "jig-a" pronounciation
for giga seems to be in more-or-less in keeping with "gigantic".

CV> The Greek pronunciation for "giga" uses hard "g" sounds, just like
CV> "Greek". Not like "gigantic". Do people use the "jig-a" way? Never
CV> heard of it.
CV> Costas

Sure some do, i.e. the professor in "Back to the Future"...

.... Is reactance then illusory? No, it just appears that way...

 

[Watson A.Name - 'Watt Sun]

In article <h13mhvkp1756970od1kjc5ifchqratgj3g@4ax.com>,
fzabkar@optussnet.com.au mentioned...

On Sun, 20 Jul 2003 12:21:18 -0700, Watson A.Name - 'Watt Sun'
alondra101@hotmail.com> put finger to keyboard and composed:

In article <3f1a8f6e.1627749@news.itd.umich.edu>, no_spam@aol.com
mentioned...
On Sun, 20 Jul 2003 08:50:43 +1000, Franc Zabkar
fzabkar@optussnet.com.au> wrote:


I would think the most sensible pronunciation would be "giga" as this
prefix is derived from the Greek word, "gigas", meaning "giant".

How do the Greeks pronounce "gigas"? The "jig-a" pronounciation
for giga seems to be in more-or-less in keeping with "gigantic".

Are there any hard-"g" English words with the "giant" meaning?

Not that anything is going to change common usage! ;-)


The NIST page doesn't show the pronunciation. Here's the URL:
http://physics.nist.gov/cuu/Units/prefixes.html

But see here: http://wombat.doc.ic.ac.uk/foldoc/foldoc.cgi?giga-
and here:
http://www.m-w.com/cgi-bin/dictionary?book=Dictionary&va=giga-
Generally speaking, the first listing in the dictionary is the
preferred pronunciation.

My Concise Oxford dictionary lists both pronunciations for "giga" as
being acceptable, although here in Australia absolutely nobody uses
the "jiga" form. My dictionary also lists both pronunciations for
kilometre, although the ki-lometter version is "disputed", for obvious
reasons.

And the following URL talks ad nauseum about the pronunciation, but
all that is moot since the reference publications from NBS (now NIST)
(which are presumably derived from the SI international stds), and
such pubs as the U.S. Navy and ASME give the prounciation as jiga.
http://www.lns.cornell.edu/spr/2001-12/msg0037637.html

I'm not sure that one could consider any US based metric reference to
be authoritative.

As I said, it is derived from the international standards.

Apart from Liberia and Myanmar (Burma), the USA is
the only other country that retains the old Imperial system of weights
and measures.

The metric system is the U.S. standard as it is in the rest of the
world, even tho the 'U.S.' system is still in common use along side of
it. See URL http://ts.nist.gov/ts/htdocs/230/235/h4402/appenc.pdf

I reckon you guys ought to pronounce *our* system the
way *we* do.

"Our" system *is* the international system. It's called SI.
See URL http://www.bipm.fr/pdf/si-brochure.pdf Page 103 gives the SI
prefixes, and there is no pronunciation shown. This *is* the official
standard. As shown on a previous page, the U.S. is a member of the
SI, and uses SI as the official standard.

The old NBS (now NIST) publications, the ASME (American Society of
Mechanical Eng'rs), the U.S. Navy, and other publications show the
pronunciation as jiga. I have those pubs and would be glad to show
the picture of the actual page that shows the pronunciation.

Does your country have a standards body? Does it have a publication?
If not, does it use the SI publication (URL above) as the standard?
If so, then your system doesn't *have* any pronunciation.

You have to realize that the language of some countries doesn't even
have some sounds that we have, and English speaking countries don't
have some sounds used in the language of other countries. And this
also doesn't take into consideration that the language of other
countries might be written in characters that bear no relation to the
'Roman' characters we use. So it would be left to the individual
countries to translate the reference materials into their own
language.

Bob Masta
tech(AT)daqarta(DOT)com


- Franc Zabkar

--
@@F@r@o@m@@O@r@a@n@g@e@@C@o@u@n@t@y@,@@C@a@l@,@@w@h@e@r@e@@
###Got a Question about ELECTRONICS? Check HERE First:###
http://users.pandora.be/educypedia/electronics/databank.htm
My email address is whitelisted. *All* email sent to it
goes directly to the trash unless you add NOSPAM in the
Subject: line with other stuff. alondra101 <at> hotmail.com
Don't be ripped off by the big book dealers. Go to the URL
that will give you a choice and save you money(up to half).
http://www.everybookstore.com You'll be glad you did!
Just when you thought you had all this figured out, the gov't
changed it: http://physics.nist.gov/cuu/Units/binary.html
@@t@h@e@@a@f@f@l@u@e@n@t@@m@e@e@t@@t@h@e@@E@f@f@l@u@e@n@t@@

 

[Bob Masta]

On Sun, 20 Jul 2003 15:52:38 -0500, "Tim Williams"
<tmoranwms@charter.net> wrote:

"Costas Vlachos" <c-X-vlachos@hot-X-mail.com> wrote in message
news:bfeu6l$sf9$1@hercules.btinternet.com...
Do people use the "jig-a" way? Never heard of it.

No? Jigawatts? ;-)

Tim

Remember, in 'Back to the Future" the Flux Capacitor
needed "1.8 Jigawatts" for the time jump. How can
anyone argue with an authority like Doc ? ;-)





Bob Masta
tech(AT)daqarta(DOT)com

D A Q A R T A
Data AcQuisition And Real-Time Analysis
Shareware from Interstellar Research
www.daqarta.com

 

[Ratch]

"Tim Williams" <tmoranwms@charter.net> wrote in message
news:vhmpjgs64q6l3a@corp.supernews.com...

"Ratch" <Watchit@Comcast.net> wrote in message
news:1PISa.108855$N7.15339@sccrnsc03...
Now here is where they crash. They first give equation (9-16) and
call
it Ohm's law. Then they say that all materials that obey equation
(9-16)
are ohmic. Well, all materials obey the resistivity equation (9-16).
Therefore by their reasoning, all materials are ohmic.

Then please, by all means possible, go out and identify all books with
misnomers and incorrect information!!!

For what purpose?

The world needs you!

Some people maybe, but not the world.

Why are
you wasting your valuable time on Usenet?

Why does anyone participate here?

Hurry! While there is still
time!!!!

Take it easy, what's the rush?

Tim

Ratch

 

[Watson A.Name - 'Watt Sun]

In article <nHFSa.95145$OZ2.20552@rwcrnsc54>, Watchit@Comcast.net
mentioned...

"Chuck Harris" <cfharris@erols.com> wrote in message
news:bfevp4$its$1@bob.news.rcn.net...
Hi Ratch,

Ratch wrote:

Wait a minute, if L&M say that Ohm's law is V=IR (which it is not),
and
materials that obey Ohm's law are "ohmic", then by L&M's definition, all
materials are ohmic because the resistance formula V=IR is always
correct
for all materials. How is a material defined as "nonohmic"? Ratch

No, not quite, ohmic materials by definition have a current density that
is *proportional* to the electric field. Or in other words have a rho
that is a simple constant.

j = E/rho, or E = j * rho

If you have a material where rho is not a simple constant, but rather is
a function of current density, you have a non-ohmic material.

I agree with what you said above.


This applies to either way of writing Ohm's law, because rho and R are
proportional to each other.

Yes, rho and R are proportional to each other, but that does not answer
the question I asked before (see the first paragraph above). How does L&M
define something as nonohmic when according to what they say, everything is
ohmic because it follows V=IR (which they say is Ohm's law).


So, as a result, if R is some function of I, the material is non ohmic.

I agree with that, but according to what you said about what L&M
writes, that never happens because all materials follow V=IR. Does L&M
mention
nonohmic materials? Ohm's law cannot be both V=IR and constant resistance
as current varies. Which one does L&M say it is? Ratch


There is no inconsistency.

Yes, according to what L&M says there is. Ratch

I think one has to look at the history of this. When Ohm's law was
defined, it's possible that non-ohmic conductors had not been
discovered. Hence everything that conducted obeyed Ohm's Law.

In that context, V=I*R would always apply. Hence at that time, it was
considered a part of Ohm's Law.

But later, things changed...

--
@@F@r@o@m@@O@r@a@n@g@e@@C@o@u@n@t@y@,@@C@a@l@,@@w@h@e@r@e@@
###Got a Question about ELECTRONICS? Check HERE First:###
http://users.pandora.be/educypedia/electronics/databank.htm
My email address is whitelisted. *All* email sent to it
goes directly to the trash unless you add NOSPAM in the
Subject: line with other stuff. alondra101 <at> hotmail.com
Don't be ripped off by the big book dealers. Go to the URL
that will give you a choice and save you money(up to half).
http://www.everybookstore.com You'll be glad you did!
Just when you thought you had all this figured out, the gov't
changed it: http://physics.nist.gov/cuu/Units/binary.html
@@t@h@e@@a@f@f@l@u@e@n@t@@m@e@e@t@@t@h@e@@E@f@f@l@u@e@n@t@@

 

[Ratch]

"Watson A.Name - 'Watt Sun'" <alondra101@hotmail.com> wrote in message
news:MPG.198584e79aa254e0989ae7@news.inreach.net...

In article <nHFSa.95145$OZ2.20552@rwcrnsc54>, Watchit@Comcast.net
mentioned...

"Chuck Harris" <cfharris@erols.com> wrote in message
news:bfevp4$its$1@bob.news.rcn.net...
Hi Ratch,

Ratch wrote:

Wait a minute, if L&M say that Ohm's law is V=IR (which it is
not),
and
materials that obey Ohm's law are "ohmic", then by L&M's definition,
all
materials are ohmic because the resistance formula V=IR is always
correct
for all materials. How is a material defined as "nonohmic"? Ratch

No, not quite, ohmic materials by definition have a current density
that
is *proportional* to the electric field. Or in other words have a rho
that is a simple constant.

j = E/rho, or E = j * rho

If you have a material where rho is not a simple constant, but rather
is
a function of current density, you have a non-ohmic material.

I agree with what you said above.


This applies to either way of writing Ohm's law, because rho and R are
proportional to each other.

Yes, rho and R are proportional to each other, but that does not
answer
the question I asked before (see the first paragraph above). How does
L&M
define something as nonohmic when according to what they say, everything
is
ohmic because it follows V=IR (which they say is Ohm's law).


So, as a result, if R is some function of I, the material is non
ohmic.

I agree with that, but according to what you said about what L&M
writes, that never happens because all materials follow V=IR. Does L&M
mention
nonohmic materials? Ohm's law cannot be both V=IR and constant
resistance
as current varies. Which one does L&M say it is? Ratch


There is no inconsistency.

Yes, according to what L&M says there is. Ratch

I think one has to look at the history of this. When Ohm's law was
defined, it's possible that non-ohmic conductors had not been
discovered. Hence everything that conducted obeyed Ohm's Law.

In that context, V=I*R would always apply. Hence at that time, it was
considered a part of Ohm's Law.

But later, things changed...

Maybe.....I don't know. But that was then, this is now. Ratch

 

[Chuck Harris]

Ratch,

It comes down to a basic ability to read and understand
algebra!

If I tell you that y = m*x + b, and I tell you the variables
are x and y, do I really have to tell you that m and b are
constants?

If they are not constants, then I have to show that they are
dependent on x (or y). To do that I would write them as:

y = m(x) * x + b(x) Which changes the character of the

equation tremendously.

L&M told you that most, but not all materials have a current
density that is proportional to the electric field. Then,
they gave you the equation:

j = (1/rho) * E (9-16)

[not:

j = (1/rho(E)) * E or j = (1/rho(j)) * E ]

and told you it (9-16) was Ohm's Law.

Really, though, whether or not R is ohmic, is immaterial,
as long as you can describe R, the relationship we all
call Ohm's law works... it has to, because R is defined
to make it work.

If you want to argue this further, you really must cite
Georg S. Ohm's research work that shows he was only
interested in being deified over materials that are
purely ohmic, and you really must cite the individual, or
group that first coined the phrase "Ohm's Law" to see what
they meant by it. Citing Resnick, or L&M, or the tooth fairy
doesn't do it. None of them were involved in the deification
process, and as a result their arguments are pure speculation,
or conjecture.

The overwhelming body of evidence in the engineering literature
of the last 100+ years suggests that E = iR is properly named
as Ohm's law, just as most of us think it is.

-Chuck


Ratch wrote:

"Chuck Harris" <cfharris@erols.com> wrote in message

Eq. (9-16) describes the current density in terms of the electric
field at a point in a conductor (Fig. 9-11). It is called Ohm's law.
materials that obey Ohm's law are usually called ohmic conductors. This
relation enables us to calculate the current flowing through a wire of
length L which is connected to two terminals - points between which
there is a potential difference V....]


Now here is where they crash. They first give equation (9-16) and call
it Ohm's law. Then they say that all materials that obey equation (9-16)
are ohmic. Well, all materials obey the resistivity equation (9-16).
Therefore by their reasoning, all materials are ohmic. They go on to say
that Ohm's law can be used to show the relationship between resisitivity,
current density, and electric field. That is certainly true for Equation
(9-16), but that is the resistivity equation and it stands on it own
independent of Ohm's law. The resistivity (9-16) is used to determine
whether a material has the Ohm's law property, but it is not Ohm's law per
se.




L&M could have said a bit more about what they meant about a material
not following Ohm's law; how they meant that a material that has a non
constant rho is non ohmic. However, I caught the meaning the first time
I read it, so it cannot have been too badly worded.


You were primed to understand it because of your exposure to this
discussion.


The trip from (9-16) to: V = RI is just a straight forward
rearrangement, and substitution. It still states the same thing as
(9-16). A material is non ohmic if R is not a constant.


I don't see L&M saying anything that corresponds to the last sentence
above. Again, the resistance equation V=IR can be used to determine if a
material has the Ohm's law property, but V=IR stands on its own and is not
Ohm's law per se. Look at
http://maxwell.byu.edu/~spencerr/websumm122/node50.html again. Ratch