# Discussion of Ohm's Law for Noobies

Discussion in 'General Electronics Chat' started by Mongrel_Shark, Jun 3, 2012.

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1. ### Mongrel_Shark Thread Starter New Member

May 30, 2012
22
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I've been playing with eletricity for 20 years. Got my first multimeter when I was 7 years old. Never understood why the different letters. I have to admit to not reading the txt or doc's properly yet. Just skimming the txt now. Seems simple enough. no disagreement from me.

But why different letters to describe the same thing? Amps are amps. A. volts are volts. V. multiply them and you get watts. W. Resistance is heat loss. like a toaster element. Resistance. R. No one can explain I or c to me in a way that makes sense....

Am I missing something?

I always saw volts as the size of the water pipe. amps as the speed, and watts as the expression of both factors combined. It's all describing Coulombs (I forget how many electrons in a coulomb). How many side by side and how fast they are traveling.

The thing that threw me off ohms law, and all of electronics after that. is this need to use 400 year old terms, created by people that didn't have half the understanding of electricity I did at age 10. (I was lucky enough to have a radio genius as an uncle to explain things to me)

I represent your nOOb. Except I get electricity in a way few people do... don't know why. maybe it's from my family. Maybe it's the hundreds of times I have been zapped, including lightning at least once (running through storm, so feet of the ground.) But the theroy has always bugged me. something is not right. it's simple, yet nobody seems to understand. all you old hands learnt the hard way. you had no choice... so you just learnt to deal with it and moved on. to me it's just not quite right. the maths works. The letters are wrong though. sorry.

20 years later I finally have the determination to tackle it again. It's not the maths that messes with me. I was doing algebra 2 years above my age before I got tired of being held back at school and got a job as a concreter at age 13. I could multiply fractions with uncomon lowest denominators since I was 11. Got failed for inventing a new way to do it when I was 13, just because the teacher didn't understnd my method. even though I taught my grandmother to use it, and my uncle (the radio guy) backed me up. said my theroy held up. just didn't show some of the workings out I may need to do year 11. so trust me the maths is easy. As a concreter I used to win arguments with engineers regularly. Based on my maths skills.

So can someone please explain to me why I now have to start calling amps intensity?

You have it 2 thirds fixed by changing volts to V. That was the worst bit. Calling volts Current is just plain wrong. Current makes me think of speed. so a big thumbs up from me on changing C to V. But I like to call a spade a spade.

Amps is speed. intensity is just confusing...

If I'm wrong correct me so maybe I'll understand better.

2. ### Mongrel_Shark Thread Starter New Member

May 30, 2012
22
2
While I'm venting my spleen.

Ground is a long rod in the earth. Or a large body of water that has contact with ground.

It is not the negative terminal on a battery. it is not a common rail negative.

Earth is planet earth and it's massive neg charge, caused by the fusion in the core. Oppisate to cosmic radiation.

Negative is a terminal on a battery or the body of a motor vehicle.

Two very different things. Only have to read Tesla to get that....

Try earthing a radiant energy collector to a neg terminal and see hoe it works....

(please excuse my lack of capitals and crappy tone. I've had a bad day, don't mean to take it out on anyone here)

3. ### MrChips Moderator

Oct 2, 2009
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4. ### Georacer Moderator

Nov 25, 2009
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I 'm not sure if we are on-topic. Time will tell.

About your post #60. Velocity is a very bad term to describe current. Current travels at a constant speed though inductors and this speed is VERY different than the speed of its carriers (electrons or holes), which isn't constant.
So, speed might be good for the "river analogy", which is taught in the elementary school, but not so good when you want to be more professional about it.

Formally, current is defined as I=dQ/dt. That is, the amount of charge passing through a surface in one time unit. This isn't dependent on the charge speed, which is actually quite slow, but mostly on the amount of charges that pass through the surface. Hence the term intensity; it refers to how much charge is passing, not how fast it is.

One last thing. I think you suggested that we use A instead of I, to refer to current? I might have misread you, but if this is the case, should the symbol of speed turn into km/h also?

5. ### Wendy Moderator

Mar 24, 2008
21,839
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I moved this from Ohm's Law sticky with LED section. If you read the article discussions of the contents should be discussed in the General Electronics Chat forum, so I moved it and related discussion here.

We've had the argument before. Thing is, no one person defines convention, it is what it is. Ground used to mean a long rod into the earth, now it means more. That is not going to change.

Ditto as to letters used to describe Ohm's Law. You can use whatever you want, it doesn't matter, but it you are talking to someone else all of a sudden it becomes critical, because like as not, they in turn will talk to other people. If everyone gets feed up with convention then things change, but the fact is it currently works.

We still have people argue that electron flow is wrong, and conventional flow is still taught in schools. There is quite a bit if physics that says other, but again, it is convention. If people hit a certain point in electronics where they need to match the laws of physics to electricity they have to relearn several things, until then it doesn't matter, and conventional current flow is taught as standard. That isn't changing either.

Convention sets the common language and concepts we all use to communicate. You can step outside of it, but when discussing issues with other people do you want to spent all your time arguing minutia, or do you want to solve the problem?

Last edited: Jun 3, 2012
6. ### crutschow Expert

Mar 14, 2008
23,130
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Your concept of electricity needs a little fine tuning.

If you want to use the water analogy-----

Volts is the water pressure.

Amperes (C/s) is flow rate of the water such as gal/s (not speed).

Ohms (V/I) is the resistance of the pipe to the flow as determined by the pipe diameter (or valve or other restriction).

Power (V*A) is pressure times the flow rate.

An inductor would be a friction-free slug moving in the pipe with the water. Its inertia to the change in water flow rate is the inductance.

A capacitor would be a water chamber with an inlet and an outlet and a flexible rubber membrane sealing the chamber between the two. The membrane allows a limited amount of water to flow in and output based upon the water pressure (volts) and the capacitance (as determined by the chamber size).

Admittedly this analogy is very limited (primarily to DC circuits) but it can help visualize the relationship between the various basic electrical parameters.

Last edited: Jun 3, 2012
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7. ### bretm Member

Feb 6, 2012
152
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I don't see it as "changing" the letters.

I is current and A is the unit of current.

E is electric potential and V is the unit.

R is resistance and Ω is the unit of resistance.

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8. ### count_volta Active Member

Feb 4, 2009
434
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NO NO NO. Its j not i. JJJJJJJJJ. arghhhhhhh. ahhhhh. yells. hits things!!! Excuse me while I kill someone.

That is really how I think when I see i used instead of j to represent sqrt(-1). That is related to your angst about I representing current.

9. ### Mongrel_Shark Thread Starter New Member

May 30, 2012
22
2
0_o

Can you say that again with more detail?

I am way to busy to start Googling obscure equations..

Not that I felt any need for help on this topic.

I just saw a thread where ohms law was being re-written with V instead of C (finally, only took a hundred years) So I thought I'd offer some feedback as someone that had recently been confused by the odd letters and lack of explanation as to why they are used in stead of just calling Amps A and Volts V.

I thought there might be a logical explanation as to why this is.

Clearly the reason in eletisim. Nothing more... If there was a logical explanation. surely someone would have posted a link or something.....

You know. To a document that explains things clearly....

That my comments got moved here, and that so few people actually care to offer usefull advice shows just how much people here want to help people get into electronics.... (ie. not at all)

10. ### t_n_k AAC Fanatic!

Mar 6, 2009
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Maybe we should discuss the value of sarcasm as a social construct.

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11. ### t_n_k AAC Fanatic!

Mar 6, 2009
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In defense of the AAC Forums I would say you get a better deal here than you would at some other less tolerant "places".

Many of us here have spent substantial time and effort helping others - absolutely gratis and with little regard to elitism.

Thanks for taking the time to make your point.

12. ### count_volta Active Member

Feb 4, 2009
434
24
I don't think it really matters man. Engineering is full of weird stuff like that. We use the same greek letter to mean 100 different things in various sub disciplines of electrical engineering.

All that really matter is that you understand what voltage is, what current is, what resistance is. I could start using the symbol ζ to mean voltage all of a sudden and it would not make any difference really.

The unit of resistance is the ohm, named after Ohm the scientist who studied resistance. The letter Ω omega is used because it sounds like ohm. Voltage is named after Allesandro Volta who invented the first battery.

Here is info on why I is used for current. Ampere himself called it "intensity". We named amps after him, but kept the symbol he used.

Why is the letter I used to represent current?

The letter I seems to be an odd choice for the English language, but it was chosen in the early days of electricity to represent intensity of current which we simply call current today. The unit of current, the ampere, is named after the French scientist André-Marie Ampère in recognition of his work on the relationship between electric current and magnetism. Ampère referred to electric current as "l'intensité du courant électrique", so I was a logical choice to represent intensité (intensity). I am grateful to Barry Caruth for suggesting a search of the internet for "Ampère" and "l'intensité du courant électrique" which returns many sites as evidence (most of them French) enabling me to answer this question with confidence.

What I meant in my previous post was a joke. Mathematicians use the letter I to represent the square root of minus 1 because it stands for imaginary, while electrical engineers use the letter j because I already means current, and when you write phasor equations you often have something like (2+3j)*I. This means an impedance of 2+3j multiplied by current. If we used i for square root of -1, we would make the mistake of thinking that you should square the current.

But mathematicians and engineers have this war going on over which letter should be used for square root of -1. Because we are both way too obsessed with notation. Its not elitism, its insanity.

Last edited: Jun 5, 2012
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13. ### Mongrel_Shark Thread Starter New Member

May 30, 2012
22
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Ignorance is bliss.

Untill you find some high voltage.

I was being straight up. Perhaps someone else was being facietious. Hence my lack of understanding.

14. ### Wendy Moderator

Mar 24, 2008
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It is about standards, nothing more. I and others said it, you can redefine Ohm's Law variables to what ever you want.

The standards have been around longer than both our ages, added. So like as not, you are better learning the standard than trying to establish new standards. If you converted one person per day the schools teaching their students will out number you and your lifetime of converts in less than a year.

Many of them don't make sense, until you dig deep. Many of them were created by very smart lonely old guys that had a concept and the first instrument of its kind in a wooden box. Almost all of them relate to math somewhere.

I will teach Ohm's Law without using the standard variables. This is because algebra doesn't care, and I don't want to get lost in explaining why voltage is E, when all I want to do is communicate how to bias up a LED or transistor.

But I know the formula. I have to, if I am going to understand someone elses work. An while I may not remember all the details, I knew them at one time, which makes refreshing my memory easy.

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15. ### ErnieM AAC Fanatic!

Apr 24, 2011
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When you represent yourself as both a "noob" and then hold contempt for "people that didn't have half the understanding of electricity I did at age 10" and ultimately ask no question...

do you actually expect an answer?

Everyday we walk people thru all the tiniest of details just "because." If you have a specific question please feel free to ask it. Don't try to elevate yourself at the same time, just ask without any drama.

It always helps to be polite to us, least we all have some "insider" fun at your expense.

16. ### bretm Member

Feb 6, 2012
152
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Georg Ohm actually wrote $S=\frac{A}{L}$, so why worry about E, V, C, I, etc.?

17. ### #12 Expert

Nov 30, 2010
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18. ### Wendy Moderator

Mar 24, 2008
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Who invented Ohm's Law? Really?

Sounds like Ratch.

At that point it becomes my job. We take trolling on AAC very seriously, it is not allowed. If someone can't hold back then I will edit or remove posts, it is better not to say anything sometimes. Of course, a straight answer can look like trolling, but isn't. Those I and my fellow moderators let pass.

There is a difference between friendly kidding and trolling. Mostly it is a matter how long someone has been here, interpreted intent, and how they have interacted with others in the past. People new to the site tend to get special protection, but they are not allowed to troll either.

One thing is straight up though, if you don't speak the lingo you don't know the subject. You may not like the lingo, but that is irrelevant. You still need to know it. A large part of school is to teach that part of the subject.

Last edited: Jun 5, 2012
19. ### cork_ie Active Member

Oct 8, 2011
428
74
Hi OP
I know it can be confusing, but over the years we have had all kinds of units of Measurements in Physics. (Ergs. anyone? )
Thankfully we have had the SI system now for over 60 years and the units are largely set in stone with very few changes since. It must also be borne in mind that not every country speaks english and everything is a compromise.

The electrical units are generally named to commemorate the great pioneers in the field. Volta, Ampére, Ohm, Faraday, Henry, Tesla , Oersted, Coulomb etc. . Watt & Joule are the exceptions as they express energy and power and are derived from the physics of heat but are directly interchangeable as electrical units to avoid duplication for the same thing.

Unfortunately. For electrical equations and calculations it just so happens, that V can mean Volts and also velocity. Similarly A can mean Amperes and area. O for ohms is far too confusing with 0. Especially in the days of pen & paper and could lead to endless simple mistakes.

(I had the privilage to have a very old maths teacher in my senior year who was a PhD student at Cambridge in the 1930's when Rutheford split the atom. He used always tell our class how large teams of up to 20 PhD maths students were required to do the maths and it took months. A PC can now days probably do the same in 60 seconds flat.)

Thus for complex electrical equations & calculations it is optional to use I instead of A as a symbol for current and E (electromotive force) instead of V for voltage aka "Potential Difference"
Ground (USA) = Earth (UK/IRL) = Terre = Masse (various European) is best understood as a common potential reference point , a bit like sea level for elevation.

20. ### crutschow Expert

Mar 14, 2008
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I is always used as a symbol for current. A stands for amperes which is the unit of current. Similarly E represents the electromotive force which is measured in Volts (V). Thus if E = 6V across R = 2Ω then I = 3A.