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

In article , snipped-for-privacy@earthlink.net mentioned...

Tsk-tsk! Siwwy wabbit! You have to unscrew the back of the meter, and remove the 9V battery, then connect the wires to it! Simple!

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Watson A.Name - 'Watt Sun'
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In article , snipped-for-privacy@bellatlantic.net mentioned...

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. 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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Watson A.Name - 'Watt Sun'

them

Good. You finally gave a valid reason for your gripe and did not deny my "factoid". I can understand and appreciate your concern and irritation. However, these threads are not just read and appreciated by you , I, and a select few. There are plenty of lurkers who don't mind learning something, and inserting ancillary facts into a discussion is not beyond what is normally done here. Look at how some of the other threads have morphed. Anyway, I don't think I was out of line in pointing out that Ohm's law is usually used as a misnomer. The choice to keep on doing so is up to the individual. Ratch

Reply to
Ratch

Hmm, probably, yes. It went out when the source of 2000V (at moderate current) was turned off.

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http://inquisitor.i.am/    |  mailto:inquisitor@i.am |             Ian Stirling.
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Ian Stirling

"Ratch" wrote in news:BZmRa.80118$Ph3.9181@sccrnsc04:

What the heck is "nonohmic"? Is this a word you just made up? I have been an electronis tech for 30+ years and thats a new one on me. It all doesn't matter. Wether it is inductance, capacitive impedance, a thermistor, a varistor, or what ever. Ohm's law still stands firm. For changing "impedance" or fixed resistance. At any moment in time, there is a certain resistance(impedance), a certain voltage and a certain current and ohm's law always applies. Even in a combined circuit of capacitance and inductance with an appplied frequency signal. At 1 instantaneous moment, there is a vectored impedance and associated voltage and current. It is a law of physics and there is no getting around it no matter what you call it. A rose is a rose is a rose. Here are the formulae and you believe what you will.

Reply to
buck rojerz

Eeww!! StinkCity!

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Reply to
Watson A.Name - 'Watt Sun'

Its one of those connie current things getting ronnie resistor ... hot. :)

Reply to
William Hayes

There was these two Engineers.... leaving the work place, they were headed home. They left the building headed out to the parking lot when the first engineer stopped at a brand new 10 speed bike, bent over and unlocked it. The second engineer looked at the first and said, "Hey, I didn't know you got a new bike." The first engineer started recounting his experience at getting the new bike, "Yeah, I was out jogging my 1/2 block down the street when a lady on this ten speed bike came by. She stopped. Got off the bike. Took all her clothes off. Stood in front of me and said to me that I could have anything I wanted." The second engineer thought for a moment and replied, " Yeah, good choice, I don't think you'd fit into any girlie clothes, either."

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... :)

Reply to
William Hayes

Probably an analog meter multimeter. You'll have to get with the program and buy a digital one. :) :)

Reply to
William Hayes

I understand there are occasionally sightings of 'wild bike riding' women when our sorts take to jogging 1/2 a block. :) :)

(I haven't tried jogging a full block ... my luck, I'd run into wild cement truck driving women ... )

Reply to
William Hayes

voltage-dependant-negative-coefficient

As I pointed out earlier, there is no "Ohm's law equation". I believe you are referring to the resistance formula R=V/I and its variations, which is not Ohm's law, although it is often mistakenly called that. Ohm's law is a property of a material as explained in

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which I posted earlier. Did you read it? Ratch

Reply to
Ratch

In article , snipped-for-privacy@OVEcfl.THISrr.com mentioned... [snip]

invented

I believe the 202 wasn't their first osc. I used a HP 200CD audio osc back in the '60s when I worked for a radio eng'g lab and it wasn't the earliest.

Whoops! You should not have said "lower its resistance". You should have said, it will lower its voltage drop. After all, it's not an ohmic device.

This is the first I've heard of the Nernst glower - never heard of it before. I did a google search and found this site, which tells a lot about this German guy. I remember that when I was in Germany, a lot of stuff had AEG on it.

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Tell me. Do you believe in negative resistance? :-)

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Watson A.Name - 'Watt Sun'

believe

which

is

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/Resistance.htm

I keep getting "Can not find server - the page you are looking for is unavailable." send me a copy.

I'm piqued. I'd like to know why you think E=I*R is not "Ohm's Law".

William Hayes, Ph.d. E&E.

"By Trying to understand the natural world around us, we gain confidence in our ability to determine whom to trust and what to believe about other matters as well. Without this confidence, our decisions about social, political, and economic matters are inevitably based entirely on the most appealing lie that someone else dishes out to us. Our appreciation of the noticings and discoveries of both scientists and artists therefore serves, not only to delight us, but also to help us make more satisfactory and valid decisions and to find better solutions for our individual and societal problems." - Frank Oppenheimer.

Reply to
William Hayes

been

I posted this site before, which answers your question.

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Did you read it?

The resistance formula R=V/I stands firm. Ohm's law is a property of a material, as explained in the above link, and is not an equation.

certain

Impedance is not a vector, it has magnitude but no direction. Impedance has magnitude and phase and is often described as a phasor, which has some vector like properties.

Yes, the resistance formula is R=V/I is R=V/I.

You are having a hell of a time posting that chart, are you not. In any case, I agree with the relationships indicated by all the formulas. I do not agree with naming them Ohm's law. Ratch

Reply to
Ratch

law

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My apologies, try this. I can also post a couple of snippets from two good physics books which back up the link. Ratch

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Reply to
Ratch

good

formatting link
/Resistance.htm

Try this :

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Pay particular attention to the part referring to George Ohm determining that the current that flows through a wire is proportional to its cross sectional area and inversely proportional to its length provided temperature remains constant. This is refereed to as Ohm's Law.

In your reference you have : His rule is "that the ratio of potential difference to the current flowing through a conductor is constant, providing all other influences such as temperature are kept constant."

While basically your reference is almost correct, it is not fully correct. A more appropriate reference would have been : The potential difference of the current flowing through the conductor is proportional to its cross sectional area and inversely proportional to its length provided temperature remains constant. However, this would negate the relative nonsense that followed in your link. While you can snippet links to other references, sit back and think about how the conductor's cross sectional area relates to the length of the conductor verses the potential difference to allow energy (electrons) to flow through the conductor with room temperature remaining constant. Once you invision it, you will have grasped Ohm's Law.

In your reference you have : This particular formula, often written as V = IR is extremely useful. It is often known (incorrectly) as "Ohm's Law".

Why ?

:)

Reply to
William Hayes

formatting link

temperature

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. The second definition is correct and states "Ohm's law stated that the amount of steady current through a material is directly proportional to the voltage across the material, for some fixed temperature". This is correct except for the I=V/R formula which is not Ohm's law. In other words, if the voltage doubles or triples, the current doubles or triples. If the current in a material does not follow the voltage in a linear fashion, it is nonohmic and does not have a straight line on a V vs I curve. On every point on that V vs I curve, I=V/R, but that formula is not Ohm's law. Many metals do plot a more or less straight line and are ohmic. Semiconductors and other materials do not and are nonohmic.

temperature

to

energy

The cross section of the conductor has no bearing whatsoever on whether a material is ohmic or not. If you have a conductor made out of a certain material, you can plot the V vs I curve. 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 you understand that resistive linearity property of the material, then you know Ohm's law.

Here's why.

I will first quote from a college textbook called Physics, by Halliday & Resnick, 1967, page 780. It was written by David Halliday, Professor of Physics, University of Pittsburgh and Robert Resnick, Professor of Physics, Rensselaer Polytechnic Institute

----------------------------------------------------------------------- "We stress the relationship V=I*R is NOT a statement of Ohm's law. A conductor obeys Ohm's law only if its V vs. I curve is linear, that is, if R is independent of V and I. The relationship R=V/I remains as the general definition of the resistance of a conductor whether or not the conductor obeys Ohm's law. . . . . . . . . Ohm's law is a specific property of certain materials and is NOT a general law of electromagnetism, for example, like Gauss's law."

-----------------------------------------------------------------------

Next a quote from another college textbook called Physics for Scientists & Engineers, by Raymond Serway, Third Edition, 1990, page 745. It was written by Raymond A. Serway of James Madison University

----------------------------------------------------------------------- "A current density J and an electric field E are established in a conductor when a potential difference is maintained across the conductor. If the potential difference is constant, the current will also be constant. Very often, the current density in a conductor is proportional to the electric field in the conductor. that is J=sigma*E where sigma is called the conductivity of the conductor. Materials that obey the above equation are said to follow Ohm's law, named after Georg Simon Ohm (1787-1854). More specifically, Ohm's law states that for many materials (including most metals) the ratio of the current density and electric field is a constant, sigma, which is independent of the electric field producing the current. Materials that obey Ohm's law, and hence demonstrate this linear behavior between E and J, are said to be ohmic. The electrical behavior of most materials is quite linear for very small changes in the current. Experimentally, one finds that not all materials have this property. Materials that do not obey Ohm's law are said to be nonohmic. Ohm's law is not a fundamental law of nature, but an empirical relationship valid only for certain materials."

-----------------------------------------------------------------------

OK, what could be clearer? Ohm's law refers to the linearity between voltage and current, not relationship between voltage, current, and resistance. Yet the formula, V = I*R has been misnamed across countless classrooms, books and discussions. What does your textbook or school teach?

To summarize, certain materials like conductive metals follow Ohm's law, in that their V vs.I curve is linear. Ohm's law is a property of a material, not a general law of nature. Other conductive entities like diode junctions or gas discharge bulbs do not have the Ohm's law property, because their conductivity changes depending on what voltage or current is applied, causing their V vs. I curve to be nonlinear. In all cases, V = I*R is always correct, but it should not be called Ohm's law.

No matter what you call V = I*R, circuits will still get designed and analyzed, and science will still progress. In any case, be aware that V = I*R is not Ohm's law, but the V vs. I linearity, if present, is the law.

Reply to
Ratch

To a technician, Ohm's Law is the set of mathematical operations which predict the behavior of voltage, current, etc. After using them for so many years, I think it's understandable that a tech would only think of the formulas and not the simple "mission statement" which would be the "statement" of Ohm's Law. I'll stick with the formulas, thank you.

Mark Z.

Reply to
Mark D. Zacharias

In article , snipped-for-privacy@comcast.net mentioned...

Heh-heh. I think I posted that or something similar a couple weeks ago.

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

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Watson A.Name - 'Watt Sun'

In article , snipped-for-privacy@comcast.net mentioned...

Oohh, Kinky!

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