Ohm's law for beginners (or the amp-hour fallacy) 2012-03-14

[bychon]

bychon submitted a new article:

Ohm's Law for Beginners (or The Amp-Hour Fallacy) - Just about once a day, somebody writes in with, “My boom box has a dead battery that says 12 volt

Just about once a day, somebody writes in with, “My boom box has a dead battery that says 12 volts, 1.8 amp-hours. The new battery says 12 volts, 2.4 amp-hours. Will the extra amp hours burn up my radio?”

No, gentle reader, amp-hours are a measure of capacity. Your new battery has an extra quart of electricity, not a high pressure nozzle.

It's like standing next to a swimming pool with a glass of water. Water represents current and you represent the radio. You (the radio) can drink a...

Read more about this article...

 

[Ratchit]

Bychon,
Calling V=IR Ohm's law is a mistake and misnomer, although just about everyone does so. V=IR or alternatively V=IZ should really be called the resistance or impedance formula respectively. It is always correct, because it is a definition of resistance or impedance. Folks have known about the resistance property of materials ever since electrical science was born. Georg Ohm did not discover, define, or disclose resistance. His contribution was the discovery that certain substances like metals had a linear relationship between voltage and current. In other words, no matter what the existing current within reasonable limits, the resistance remained the same. Substances that have this property are said to be ohmic, and obey Ohm's law. Other things like semiconductors and gas discharge tubes do not obey Ohm's law, because their resistance or impedance varies along the V-I curve. Nevertheless, all conductors are defined by the resistance or impedance formula V=IR or V=IZ, which is not Ohm's law.

A couple of good college level physics books by Haliday & Resnik and Raymond Serway concisely emphasize the fact that Ohm's law is a property of a material (linearity), and not a general law of electrical science like Gauss's law. They also emphatically state that transistors, vacuum tubes, and thermistors do not obey Ohm's law. I can cite these references more precisely if anyone cares to know.

Ratch
Hopelessly Pedantic

 

[bychon]

and you think this will help noobies how....?

Please don't crap this up with Godnose how many arguments about the most esoteric gobbldeygook you can think of. It's for NOOBIES!!!

 

[Ratchit]

and you think this will help noobies how....?

Please don't crap this up with Godnose how many arguments about the most esoteric gobbldeygook you can think of. It's for NOOBIES!!!

Bychon,

You wrote: "and you think this will help noobies how....?"

My answer: It announces to everyone that Ohm's law is not V=IR . Notice that no one says V=IR is not correct or useful, just that it is a misnomer with respect to calling it Ohm's law. Don't you think that confusing a property of a material with a definition of resistance is something to discuss and wonder about?

You wrote: "Please don't crap this up with Godnose how many arguments about the most esoteric gobbldeygook you can think of. It's
for NOOBIES!!!

My answer: From Webster's Unabridged Dictionary--gob·ble·de·gook n.
language characterized by circumlocution and jargon, usually hard to understand: the gobbledegook of government reports.

—Syn. gibberish, doubletalk, bosh, mumbo jumbo.

Did you not understand my point that Ohm's law concerns electrical linearity, not a definition of resistance? If you don't agree with that, then you should present arguments against that proposition, not say you don't understand it. Don't shoot the messenger. Instead argue against the message.

I am not alone in my understanding of Ohm's law. See post #22 of the following thread for a verbatim quote from two good physics books.

https://www.electro-tech-online.com/threads/ohms-law.430/

The following are two web sites that are also enlightened.

**broken link removed**

**broken link removed**

Ratch
Hopelessly Pedantic

 

[bychon]

I understand Ohm's Law, but I wrote this paper for people that are having trouble fixing the tail light on their pick-up truck. I DO NOT think that kind of person needs to examine misnomers with respect to: properties of material, general science, vacuum tubes, thermistors, etc.

If you want to write a treatise on the misnomers of whatever, write it. I'm sure the noobies will seek it out in droves.

 

[RichTheDude]

This article is not aimed at someone who is actively going to seek out definitions or bother to read books. They just want to know if their battery is going to damage their radio (I get asked similar questions sometimes!).

 

[EvanTheElectrician]

inches = feet x 12???????

 

[cobra1]

shouldnt that be

feet = inches x 12 lol

 

[Sceadwian]

Bychon, there are at least a half dozen statements in the article that are straight up wrong and misleading. You can't lie to idiots to make them learn. If they don't understand the truth then that's their problem. There is one simple solution to this that is PERFECT. Simply NEVER EVER call it Ohm's law.

 

[bychon]

Thanks

This article is not aimed at someone who is actively going to seek out definitions or bother to read books. They just want to know if their battery is going to damage their radio (I get asked similar questions sometimes!).

I am very grateful for ONE vote of confidence. ONE person who understands how to reach out to beginners instead of indulging their need to sound all intellectual and sophistocated. Thank you!

 

[bychon]

New Law

Bychon, there are at least a half dozen statements in the article that are straight up wrong and misleading. You can't lie to idiots to make them learn. If they don't understand the truth then that's their problem. There is one simple solution to this that is PERFECT. Simply NEVER EVER call it Ohm's law.

What do you have in mind? It would have to be something the noobies can google and find a workable equasion. Perhaps Sceadwian's Law?

 

[bychon]

New Law

Duplicate...so I deleted it.

 

[bychon]

Thank you Cobra, and a special thanks to Evan for providing an equasion. The next time I measure a 30 inch door, I will plug that into your equasion:
Feet = inches x 12
Feet = 30 x 12
Feet = 360

(Ring....Ring...)
Hello. I need a 360 foot door.

 

[Sceadwian]

bychon, you can not teach by lieing to people, even if you think you have their best interests at heart. Often when teaching things are not mentioned too much to avoid confusing a begginer, but there are too many statements made in the article that are blatantly false, do not have anything to do with reality and should never be mentioned because if ANYONE that reads it goes on to further learning they're going to be confused because the information you gave them is misleading to what is actually occurring, and the terms involved so they'll have to relearn the proper way since you taught them the improper way. It is not easy writing technical documents that the layperson can understand but I'm sorry you do not have this nack =) There are plenty of VERY good and easy to understand resources available on the Internet that are not that difficult for the layperson to understand if they're willing to learn a little bit in the process. These terms are not overly technical and no one is trying to sound sophisticated. There are proper terms to use and ways to explain things and there is NO way around that.

It's like you're teaching a car mechanic calling one component a thingamabob instead of it's proper name, or instead of saying the word rotations you use the term 'spinny bit' There is no way you can write a document for someone that can't be bothered using a dictionary or Wikipedia to find out what certain things mean, there is no way to teach someone that can't do that. The only thing that type of person will EVER be able to do with electronics is assemble a kit with step by step written directions. Teach a car mechanic like that and he'll never be able to talk to any other mechanic because they'll have no clue what they're talking about.

You can't just dumb it down, it doesn't work.
The best thing you can do when someone asks a question that makes utterly no sense to even the most basic knowledge of the subject (such as power supply amperage and load demand) the BEST thing you can possibly do is give them their answer and let them go on there merry way. Users here tend to avoid doing too much work for a poster that is clueless, but someone that just wants something quick and dirty will often get simple schematics or howtos, and that's ALL they should get, not lessons with inappropriate terminology and improper usage.

If you want to teach Ohm's law it should be much simpler than that.

It should start with.

George Ohm was a physicist and experimental scientist who lived roughly in the first half of the 19th century. He is famously known for Ohm's Law, which from his experiments showing that the current developed through a fixed resistance will under controlled conditions be approximately linear to the voltage applied to it; from Ohm's work the following equations were found to be generally true and very important for simple circuit analasys. They are, I=V/R, V=I*R, and R=V/I although these equations can be used for a great number of purposes in analyzing circuits a device is only considered to be "Ohmic" if the resistance portion of the equation is a fixed value over it's operating conditions.

Well that'd be my first edit at least. To say anything else is skirting the truth of what is under discussion.

 

[bychon]

I think you better take this up with the moderators of this site. After I presented this article to them, they asked me to post it. ElectroMaster even helped with the formatting. I'm sure ElectroMaster and Mikebits will be eager to discuss this with you.

While you're at it, you can hopefully come to an agreement about what to call this thing about amps and ohms and volts that apparently isn't Ohm's Law.

 

[Dx3]

OMG! He played the God card!

Pre-approved by the highest authority on the site!

 

[Sceadwian]

Odd, it won't let my send you a private message for some reason, possibly your security options or I wouldn't have posted this response in the article.
I don't need to take it up with anyone Bychon, I wasn't even going to say anything until Ratchit chimed in and you responded to his comments in the manner you did which do not make logical sense to me. I said what I think and I'll leave it at that.

 

[bychon]

I turned off my personal messages because I am not here to argue with anybody. (Gee, how did I guess somebody would try to go personal with this?) I only posted this article to help the new guys (and girls). I didn't actually read the diatribes agains the use of "Ohm's Law" as a label for this relationship between amps, ohms, and volts. I only asked that people not try to confuse the beginners.

As soon as you have the new label for the amp/ohm/volt relationship, I hope you will post it here so the noobies will know where to look for a better understanding. That is the only thing I am interested in...where the noobies can look for a better understanding.

 

[Sceadwian]

Bychon you don't seem to understand what's occurring here. You're the one confusing newbs. You could simple say they're equations derived from Ohm's law. You're making this huge deal out of something that is not only trivial but not as complex as you're making it out to be.

 

[bychon]

Procedures are in place.

There are procedures in place for your concerns. If you are a beginner and this article confuses you, you can post your questions in a forum, possibly "chat" or "theory". If you are not a beginner and you believe there is something inappropriate in the article, report it to the moderators. It is their job to remove inappropriate posts.