Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems.

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  #81   Report Post  
William Hayes
 
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Default Turn Your Power Supply into an Ohmmeter - It's Free!


"Watson A.Name - 'Watt Sun'" wrote in message
So, now that we've had a nice discussion about ohm's law, explain that
fangled volt/amps rating on stuff.
I'm sure someone will note it is "nonohmic" somewhere...


So if a regular diode is nonohmic, what's a schottky diode? Half a
nonohmic? Sort of like the sound of one hand clapping... ;-)


Hey, with this new fangled Newer Math, It wouldn't surprise me.
I'm still getting used to the idea of three Ohm's Laws....



  #82   Report Post  
Chuck Harris
 
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Default Turn Your Power Supply into an Ohmmeter - It's Free!

Hi Ratch,

I pulled out my old college physics text just to see what they had
to say, and Lobkowicz and Melissinos, "Physics for Scientists and
Engineers", Vol 2. starts out stating that Ohm's Law is:

j = E/rho, and therefore, E = j * rho

Where j is the current density, E is the electric field, and rho is
the resisitivity.

Then they set a few conditions to make the math easier: a homogeneous
material of constant crossection, and some unspecified length,
and derive the more familiar form:

V = [rho L I]/A = RI, where L is length, I is current, A is
cross sectional area, and R is resistance.

V = RI

From that point on, L&M use the two forms of the equation
interchangably... picking which ever one makes the solution
easier.

So, it would appear that both forms are actually equivalent,
one is more favorable for use in studing materials, and the
other is better for studying circuitry.


-Chuck



Ratch wrote:

It is certainly true that what a professor writes is going to be what
he believes to be factual. And impossible to discern how he came upon his
knowledge. But you have to ask yourself, why did Professors Resnick and
Serway go out of their way to make a point that Ohm's law is a property of a
material and not V=IR? Does that not indicate that they looked into the
matter more closely that their contemporaries? The next time I get to a
good college library, I will look at other college physics textbooks. Ratch



  #83   Report Post  
William Hayes
 
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"Mark Jones" 127.0.0.1 wrote in message
...
William Hayes wrote:
"Frank Bemelman" wrote in
message ...
Let's go all nuts and talk about ohmistance & ohmistors from
now on

Cripes, You want these guys/gals to actually learn something
??

Did I hear someone say "MHO's?" : )


Hey, next you'll be getting into why Holes Flow.... STOP STOP... I didn't
pun that.. did I ??



  #84   Report Post  
William Hayes
 
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"Ratch" wrote in message
et...

Your link gives two definitions of Ohm's law. The first is the one you
refer to above, in that R=resistivity*length/area. It is a resistance
formula for a conductor with known physical dimensions and resistivity,

but
it is not Ohm's law. .


Dead Banana. ( beating a dead horse dry )

After all, you are calling "the" English [ liars. ]

They coined Potential of Current to Flow = current * resistively of
length/area while Temperature is constant as Ohm's Law.
E = I * R
Voltage = Current * Resistance

"The" English named it after George Ohm.

What part did you fail to grasp ?

The cross section of the conductor has no bearing whatsoever on whether a

material is ohmic or not.

So a Cross Sectional Area of a 00awg Cable has the same ohmic value at
20,000 feet as a 24awg cable at 20,000 feet ?
Surely I'm missing your point.

If you have a conductor made out of a certain material, you can plot the V

vs I curve.

Using what gauge of certain material ?
Using what Temperature Conditions ??
Ever seen a P4 Processor smoke when a fan is not applied to it after a few
minutes of run time ??

If the curve is straight, it is ohmic regardless what the physical

dimensions are--even if the cross section varies from point to point.

If the curve is straight, even if the curve is straight.
This means your processor can not function. It is breaking your Ohm's Law.

If you understand that resistive linearity property of the material, then

you know Ohm's law

I understand the resistive linearity of certain materials that conduct
electrons verses certain materials that do not conduct electronics and each
has a chart that relies heavily on the Gauge of the material and
Temperature.

If you have a conductor made out of a certain material, you can plot the V

vs I curve.

I have a conductor made of air, using 240,012 volts of potential energy
flow, you claim I can determine the plot of Voltage verses Current. Without
having to know the gauge of the air or temperature and why either has an
effect on the current flowing between the potential energy flows. Benjamin
Franklin wrote several papers regarding such flows. You'll find them
interesting.




  #85   Report Post  
Ratch
 
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Default Turn Your Power Supply into an Ohmmeter - It's Free!


"Chuck Harris" wrote in message
...
Hi Ratch,

I pulled out my old college physics text just to see what they had
to say, and Lobkowicz and Melissinos, "Physics for Scientists and
Engineers", Vol 2. starts out stating that Ohm's Law is:

j = E/rho, and therefore, E = j * rho

Where j is the current density, E is the electric field, and rho is
the resisitivity.

Then they set a few conditions to make the math easier: a homogeneous
material of constant crossection, and some unspecified length,
and derive the more familiar form:

V = [rho L I]/A = RI, where L is length, I is current, A is
cross sectional area, and R is resistance.

V = RI

From that point on, L&M use the two forms of the equation
interchangably... picking which ever one makes the solution
easier.

So, it would appear that both forms are actually equivalent,
one is more favorable for use in studing materials, and the
other is better for studying circuitry.


Every solid had a property called resistivity. Resistance is determined by
the resistivity, the shape of the solid, and the
placement of the two measurement leads into the solid.

Prof Serway says the same thing about resistance/resistivity as L&M, except
Serway does not call the formula E=rho*J Ohm's law. Instead Serway says
that if the resistivity (rho) is constant at any electric field (E), then
the material is ohmic. That means that E and J are linearly proportionate to
each other. How does L&M define an ohmic material? Ratch





  #86   Report Post  
Ratch
 
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Default Turn Your Power Supply into an Ohmmeter - It's Free!


"William Hayes" wrote in message
news:seoSa.89583$OZ2.18630@rwcrnsc54...

"Ratch" wrote in message
et...

Your link gives two definitions of Ohm's law. The first is the one you
refer to above, in that R=resistivity*length/area. It is a resistance
formula for a conductor with known physical dimensions and resistivity,

but
it is not Ohm's law. .


Dead Banana. ( beating a dead horse dry )


??? I have not idea what you mean by the above.


After all, you are calling "the" English [ liars. ]


Who are these "English" people you refer to? A lie is a willful statement
contrary to what one knows to be true. I never called anyone a liar here.
Mistaken perhaps, but not a liar.


They coined Potential of Current to Flow = current * resistively of
length/area while Temperature is constant as Ohm's Law.
E = I * R
Voltage = Current * Resistance


What is "Potential of Current to Flow"? Current exists, it does not
flow. Charge flows.


"The" English named it after George Ohm.


I know that the MKS unit of resistance was name after George. And George
stated that for some materials, the current is
proportionate to the voltage. I don't know who named that material property
after him, do you?


What part did you fail to grasp ?


Whatever you are talking about above.


The cross section of the conductor has no bearing whatsoever on whether a

material is ohmic or not.

So a Cross Sectional Area of a 00awg Cable has the same ohmic value at
20,000 feet as a 24awg cable at 20,000 feet ?
Surely I'm missing your point.


Yes, you certainly are. I am saying that whatever shape the material is
does not affect whether it is ohmic or not. I never said that same length
cables with different diameters made out of the same material will not have
different resistance values.


If you have a conductor made out of a certain material, you can plot the

V
vs I curve.

Using what gauge of certain material ?
Using what Temperature Conditions ??


Doesn't matter. No matter what the shape of the conductor, a V vs I
curve can be plotted.

Ever seen a P4 Processor smoke when a fan is not applied to it after a few
minutes of run time ??


Nope, why should that matter?


If the curve is straight, it is ohmic regardless what the physical

dimensions are--even if the cross section varies from point to point.

If the curve is straight, even if the curve is straight.
This means your processor can not function. It is breaking your Ohm's

Law.

Don't let your mind wander. We are talking about Ohm's law applied to
solids, not to computers.


If you understand that resistive linearity property of the material,

then
you know Ohm's law

I understand the resistive linearity of certain materials that conduct
electrons verses certain materials that do not conduct electronics and

each
has a chart that relies heavily on the Gauge of the material and
Temperature.


The resistive linearity is a property of the material that relies on no
chart whatsoever.


If you have a conductor made out of a certain material, you can plot the

V
vs I curve.

I have a conductor made of air, using 240,012 volts of potential energy
flow, you claim I can determine the plot of Voltage verses Current.

Without
having to know the gauge of the air or temperature and why either has an
effect on the current flowing between the potential energy flows.

Benjamin
Franklin wrote several papers regarding such flows. You'll find them
interesting.


A volt is not a unit of potential energy per se. Remember charge flows,
current doesn't, current just exists. Anyway,
sure you can measure the voltage and current of an arc with the right
equipment and safety precautions. What does does
gauge and air temperature have to do with that? Ratch


  #87   Report Post  
 
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"Watson A.Name - 'Watt Sun'" wrote:


Hey, I like that.. It has a nice ring to it: "Watson Ohmmeter".

One of the maintenance guys at work gave me a Fluke 23 meter which is
just a yellow cased version of the 73, I believe. Said he sent it to
Fluke but they sent it back because it it was beyond repair or it
would cost more than a new meter. He might have done something really
stoopid like set it to the ohms range and put it on the 480VAC. In
any case, the display comes on, but nothing happens when the test
leads are connected to a V source. Apparently something major has
been zapped. It's been laying around at work for a couple years, it
probably oughtta be tossed in the trash can.


NO NO NO NO NO!!!!
You could put some of your LEDs in the holes where the
meter leads go, make them blink or change colors or something,
and pass the thing off as an experimental DMM that uses
leds instead of leads - it reads the circuit by reflected
light! And the only difference is the letter a :-)

Seriously - it might be a simple repair. As far as the
grungy case - I have on old Fluke 8022 B whose case was
filthy. I took the guts out and washed the thing in a
bucket of hot water with dishwashing soap. I let it soak
for a couple of hours, then scrubbed it with a scrub
brush. Came out clean as a whistle.





The case is kind of
grubby so it's not worth saving for the case. Maybe I should give it
to the theater dept to use as a prop.

Recently the theater guy came over and asked our help desk lady for a
dozen telephone handsets and curly cords. She asked him what they
were going to do with them. He said they were going to use them as
props in a play, the actors would be dancing around with the handset
and the curly cord on stage. He said they would give them back after
the play was over.

Maybe they were going to imitate that Sprint guy: "Can you hear me
now?"...

--
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Don't be ripped off by the big book dealers. Go to the URL
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  #88   Report Post  
Watson A.Name - 'Watt Sun'
 
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In article ,
lid mentioned...
"Ratch" schreef in bericht
news:xscSa.97708$Ph3.10866@sccrnsc04...

"Chuck Harris" wrote in message
...


If you ask engineers what is Ohm's law, they will say E = iR,


Only because they learned it that way. If you explained the

misnomer,
then what would they say?


...they'd say you're a pain in the butt. You belong to the same category
as the ones that always have to say that RS232 is about voltage levels
and has nothing to do with serial ports. Strictly that is correct, but
at the the same time the *entire* world uses the term when referring
to typical serial ports such as COM1 and COM2 on your PC.

E = I * R. Ohm's Law. Always has been, and always will be.


And to think that I started this whole 'discussion' with just a..
oh well, forget it.

Same thing happened with the RJ-45 plugs for Cat5 cables.


--
Thanks,
Frank Bemelman
(remove 'x' & .invalid when sending email)



--
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###Got a Question about ELECTRONICS? Check HERE First:###
http://users.pandora.be/educypedia/e...s/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@@
  #89   Report Post  
Watson A.Name - 'Watt Sun'
 
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Default Turn Your Power Supply into an Ohmmeter - It's Free!

In article ,
mentioned...

"Frank Bemelman" wrote in message
...
"Ratch" schreef in bericht
news:xscSa.97708$Ph3.10866@sccrnsc04...

"Chuck Harris" wrote in message
...


If you ask engineers what is Ohm's law, they will say E = iR,

Only because they learned it that way. If you explained the

misnomer,
then what would they say?


...they'd say you're a pain in the butt. You belong to the same category
as the ones that always have to say that RS232 is about voltage levels
and has nothing to do with serial ports. Strictly that is correct, but
at the the same time the *entire* world uses the term when referring
to typical serial ports such as COM1 and COM2 on your PC.


And you would rather blame the messenger than appreciate the message.

E = I * R. Ohm's Law. Always has been, and always will be.


You are in denial. Ratch


And you really are turning into a pain in the butt. At least you're
on topic.

It kind of reminds me of all the spam artlcies in the newsmedia.
They're arguing about the definition of spam, as the whole world is
drowning in it!

There's so much bickering going on, that one would think that no one
understands the problem. I wouldn't be surprised if the lawmakers did
the same thing they've done the last few years: skip it for now and
worry about it later.


--
Thanks,
Frank Bemelman
(remove 'x' & .invalid when sending email)


--
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###Got a Question about ELECTRONICS? Check HERE First:###
http://users.pandora.be/educypedia/e...s/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@@
  #90   Report Post  
Tim Williams
 
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Default Turn Your Power Supply into an Ohmmeter - It's Free!

"Fred Abse" wrote in message
newsan.2003.07.19.11.29.21.68081.645@cerebrumcon fus.it...
Did I hear someone say "MHO's?" : )


They were nice! Shame we have to call 'em Siemens these days


- Does the girl want Mho Siemen...?

Tim

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




  #91   Report Post  
Tim Williams
 
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Default Turn Your Power Supply into an Ohmmeter - It's Free!

wrote in message
...
and pass the thing off as an experimental DMM that uses
leds instead of leads -


No no no no no... you've got it all wrong... L - E - D. Not le[a]d.
;-p

Tim

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


  #92   Report Post  
Bob Masta
 
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Default Another twist in the topic (Was Turn Your Power Supply into an Ohmmeter - It's Free!

On Sun, 20 Jul 2003 08:50:43 +1000, Franc Zabkar
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! ;-)



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
  #93   Report Post  
Ratch
 
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Default Turn Your Power Supply into an Ohmmeter - It's Free!


"Watson A.Name - 'Watt Sun'" wrote in message
.. .
In article ,
mentioned...

"Frank Bemelman" wrote in message
...
"Ratch" schreef in bericht
news:xscSa.97708$Ph3.10866@sccrnsc04...

"Chuck Harris" wrote in message
...

If you ask engineers what is Ohm's law, they will say E = iR,

Only because they learned it that way. If you explained the
misnomer,
then what would they say?

...they'd say you're a pain in the butt. You belong to the same

category
as the ones that always have to say that RS232 is about voltage levels
and has nothing to do with serial ports. Strictly that is correct, but
at the the same time the *entire* world uses the term when referring
to typical serial ports such as COM1 and COM2 on your PC.


And you would rather blame the messenger than appreciate the

message.

E = I * R. Ohm's Law. Always has been, and always will be.


You are in denial. Ratch


And you really are turning into a pain in the butt. At least you're
on topic.


I am just defending my position.


It kind of reminds me of all the spam artlcies in the newsmedia.
They're arguing about the definition of spam, as the whole world is
drowning in it!


No one has to read'em.


There's so much bickering going on, that one would think that no one
understands the problem. I wouldn't be surprised if the lawmakers did
the same thing they've done the last few years: skip it for now and
worry about it later.


Everyone understands the problem, but no one really knows of a
solution, or has the authority to implement it, or has the will and energy
to follow through on what should be done. Ratch



  #94   Report Post  
Chuck Harris
 
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Default Turn Your Power Supply into an Ohmmeter - It's Free!

Ratch wrote:

Every solid had a property called resistivity. Resistance is determined by
the resistivity, the shape of the solid, and the
placement of the two measurement leads into the solid.

Prof Serway says the same thing about resistance/resistivity as L&M, except
Serway does not call the formula E=rho*J Ohm's law. Instead Serway says
that if the resistivity (rho) is constant at any electric field (E), then
the material is ohmic. That means that E and J are linearly proportionate to


The equation:

E = rho * j

says that for a constant rho, E is proportional to j. Serway is just
putting the equation to words.

each other. How does L&M define an ohmic material? Ratch


L&M say that, "Materials that obey Ohm's Law are usually called ohmic
conductors. This relation (Ohm's law) 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."

He then goes on to derive E = R * I from E = rho * j.

If you define R = rho * L/A, (R = rho * length/crossectional area)

and realize that V = |E| * L, (V = electric field strength * length)

you get:

V = rho * (L/A) * I = V = R * I, Ohm's law.

-Chuck





  #95   Report Post  
Ratch
 
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"Chuck Harris" wrote in message
...
Ratch wrote:

Every solid had a property called resistivity. Resistance is determined

by
the resistivity, the shape of the solid, and the
placement of the two measurement leads into the solid.

Prof Serway says the same thing about resistance/resistivity as L&M,

except
Serway does not call the formula E=rho*J Ohm's law. Instead Serway

says
that if the resistivity (rho) is constant at any electric field (E),

then
the material is ohmic. That means that E and J are linearly

proportionate to

The equation:

E = rho * j

says that for a constant rho, E is proportional to j. Serway is just
putting the equation to words.


Serway also writes the equation which I did not quote, with the
stipulation that E and J are linearly proportionate.


each other. How does L&M define an ohmic material? Ratch


L&M say that, "Materials that obey Ohm's Law are usually called ohmic
conductors. This relation (Ohm's law) 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."

He then goes on to derive E = R * I from E = rho * j.

If you define R = rho * L/A, (R = rho * length/crossectional area)

and realize that V = |E| * L, (V = electric field strength * length)

you get:

V = rho * (L/A) * I = V = R * I, Ohm's law.


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




  #96   Report Post  
Watson A.Name - 'Watt Sun'
 
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Default Another twist in the topic (Was Turn Your Power Supply into an Ohmmeter - It's Free!

In article ,
mentioned...
On Sun, 20 Jul 2003 08:50:43 +1000, Franc Zabkar
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 he http://wombat.doc.ic.ac.uk/foldoc/foldoc.cgi?giga-
and he
http://www.m-w.com/cgi-bin/dictionar...onary&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/e...s/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@@
  #97   Report Post  
Costas Vlachos
 
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Default Another twist in the topic (Was Turn Your Power Supply into an Ohmmeter - It's Free!

"Bob Masta" wrote in message
...
On Sun, 20 Jul 2003 08:50:43 +1000, Franc Zabkar
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


  #98   Report Post  
Tim Williams
 
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Default Turn Your Power Supply into an Ohmmeter - It's Free!

"Ratch" 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


  #99   Report Post  
Tim Williams
 
Posts: n/a
Default Another twist in the topic (Was Turn Your Power Supply into an Ohmmeter - It's Free!

"Costas Vlachos" wrote in message
...
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


  #100   Report Post  
Chuck Harris
 
Posts: n/a
Default Turn Your Power Supply into an Ohmmeter - It's Free!

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



  #101   Report Post  
Franc Zabkar
 
Posts: n/a
Default Another twist in the topic (Was Turn Your Power Supply into an Ohmmeter - It's Free!

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

In article ,
mentioned...
On Sun, 20 Jul 2003 08:50:43 +1000, Franc Zabkar
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 he http://wombat.doc.ic.ac.uk/foldoc/foldoc.cgi?giga-
and he
http://www.m-w.com/cgi-bin/dictionar...onary&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.
  #102   Report Post  
Ratch
 
Posts: n/a
Default Turn Your Power Supply into an Ohmmeter - It's Free!


"Tim Williams" wrote in message
...
"Ratch" 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



  #103   Report Post  
Ratch
 
Posts: n/a
Default Turn Your Power Supply into an Ohmmeter - It's Free!


"Chuck Harris" wrote in message
...
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


  #104   Report Post  
Chuck Harris
 
Posts: n/a
Default Turn Your Power Supply into an Ohmmeter - It's Free!

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



  #105   Report Post  
Asimov
 
Posts: n/a
Default Another twist in the topic (Was Turn Your Power Supply into an

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

CV From: "Costas Vlachos"
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...



  #106   Report Post  
Ratch
 
Posts: n/a
Default Turn Your Power Supply into an Ohmmeter - It's Free!


"Chuck Harris" wrote in message
...
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





  #107   Report Post  
Tim Williams
 
Posts: n/a
Default Turn Your Power Supply into an Ohmmeter - It's Free!

"Ratch" 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


  #108   Report Post  
Watson A.Name - 'Watt Sun'
 
Posts: n/a
Default Another twist in the topic (Was Turn Your Power Supply into an Ohmmeter - It's Free!

In article ,
mentioned...
"Costas Vlachos" wrote in message
...
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:###
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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@@
  #109   Report Post  
Watson A.Name - 'Watt Sun'
 
Posts: n/a
Default Another twist in the topic (Was Turn Your Power Supply into an Ohmmeter - It's Free!

In article ,
mentioned...
On Sun, 20 Jul 2003 12:21:18 -0700, Watson A.Name - 'Watt Sun'
put finger to keyboard and composed:

In article ,

mentioned...
On Sun, 20 Jul 2003 08:50:43 +1000, Franc Zabkar
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 he http://wombat.doc.ic.ac.uk/foldoc/foldoc.cgi?giga-
and he
http://www.m-w.com/cgi-bin/dictionar...onary&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/e...s/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@@
  #110   Report Post  
Bob Masta
 
Posts: n/a
Default Another twist in the topic (Was Turn Your Power Supply into an Ohmmeter - It's Free!

On Sun, 20 Jul 2003 15:52:38 -0500, "Tim Williams"
wrote:

"Costas Vlachos" wrote in message
...
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


  #111   Report Post  
Ratch
 
Posts: n/a
Default Turn Your Power Supply into an Ohmmeter - It's Free!


"Tim Williams" wrote in message
...
"Ratch" 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






  #112   Report Post  
Watson A.Name - 'Watt Sun'
 
Posts: n/a
Default Turn Your Power Supply into an Ohmmeter - It's Free!

In article nHFSa.95145$OZ2.20552@rwcrnsc54,
mentioned...

"Chuck Harris" wrote in message
...
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...

--
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###Got a Question about ELECTRONICS? Check HERE First:###
http://users.pandora.be/educypedia/e...s/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@@
  #113   Report Post  
Ratch
 
Posts: n/a
Default Turn Your Power Supply into an Ohmmeter - It's Free!


"Watson A.Name - 'Watt Sun'" wrote in message
.. .
In article nHFSa.95145$OZ2.20552@rwcrnsc54,
mentioned...

"Chuck Harris" wrote in message
...
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



  #114   Report Post  
Chuck Harris
 
Posts: n/a
Default Turn Your Power Supply into an Ohmmeter - It's Free!

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" 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



  #115   Report Post  
Chuck Harris
 
Posts: n/a
Default Another twist in the topic (Was Turn Your Power Supply intoan Ohmmeter - It's Free!

And to further the anecdotal evidence:

With exception for one engineer that pronounced it jiga,
giga (pronounced like giggle) cycles per second is the only way
I heard it pronounced in the labs in the '60s. In the '70s when
Hertz became the fashion, it has always been "giga (pronounced like
giggle) hertz.

I have heard more than a few pronounce it "gigawiggles per second",
though.

I suspect that living in a southern US local that if we engineers
here started to use the "jiga" pronounciation with a regular basis, we
would end up being fired for using a racial slur. Kind of like
the D.C. mayor's aid that got fired for making the mistake of using
the word "niggardly" amoung the ignorant masses.

-Chuck

Watson A.Name - 'Watt Sun' wrote:
In article ,
mentioned...

"Costas Vlachos" wrote in message
...

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



--






  #116   Report Post  
Franc Zabkar
 
Posts: n/a
Default Another twist in the topic (Was Turn Your Power Supply into an Ohmmeter - It's Free!

On Mon, 21 Jul 2003 04:34:13 -0700, Watson A.Name - 'Watt Sun'
put finger to keyboard and composed:

In article ,
mentioned...


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.


I doubt you will find any *international* standard where giga is
pronounced jiga. Unfortunately I can't find any non-US standard on the
Net, so I can't support my claim.

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


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.


All of these are US standards. You may as well suggest that speakers
of UK English revert to US spelling amendments such as "color" instead
of "colour", for example, or that the British alter their gallon to be
in line with the US measure, or that the world play football the
American way. Having said that, I believe simplicity should be the
primary determinant of language, which means that color makes more
sense than colour, but giga is better than jiga. Hopefully common
usage will eventually eliminate the latter.


- Franc Zabkar
--
Please remove one 's' from my address when replying by email.
  #119   Report Post  
Watson A.Name - 'Watt Sun'
 
Posts: n/a
Default Another twist in the topic (Was Turn Your Power Supply into an Ohmmeter - It's Free!

In article qg_Sa.3645$Fy1.168899@localhost,
mentioned...
Watson A.Name - 'Watt Sun' wrote:
In article ,

mentioned...
"Costas Vlachos" wrote in message
...
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.


The only place I ever heard it pronounced jiga was in the Back To The Future
movies!


My dictionary, Webster's New Collegiate, shows both, but jiga is
first, and it says that the first is the preferred pronunciation.
Many dictionaries are like this, some don't even have the second.
Perhaps the people in the movie had the simple foresight to simply
consult a dictionary when they made the movie.

--
@@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/e...s/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@@
  #120   Report Post  
Ratch
 
Posts: n/a
Default Turn Your Power Supply into an Ohmmeter - It's Free!


"Chuck Harris" wrote in message
...
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.


I think you are refering to the "relationship" as being the equation.
That is not Ohm's law, the linearity property is.


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.


And how does anyone do that? How would I track something like that
down and interview folks that have been dead for such a long time? One can
assume that it is called Ohm's law because he was the one that proposed that
current is proportional to voltage for many materials.

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.


I hope you mean giving credit where credit is due as being the
"deification process" Resnick and L&M are experts in their field, and their
opinions should be taken into account and evaluated. You can argue that
they did not explain things well enough, or are mistaken, or even careless.
But you cannot realistically say their writtings on this subject are
imaginary, like the tooth fairy.


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.


I think the overwhelming evidence is that resistance formula has been
wrongly named for a long time now. Ratch


-Chuck


Ratch wrote:
"Chuck Harris" 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





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