Make Ohm's Law FAQ available

[bychon]

Recent exchange prompts me to discuss the fact that about once a day, we get a post by a person who thinks that if a battery is rated at 10 amp-hours, anything connected will have 10 amps forced through it. Other Person suggested a FAQ be made available for noobies that don't know Ohm's Law. I very much agree and wish I could refer posters to a FAQ or Tutorial about E=IR and P=IE. It would have to be written in very, very basic language. I would happily leave that job to someone else.

 

[JimB]

People have been part way ther already and look at the commotion it caused:

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

I would not touch it with a barge pole.

JimB

 

[Sceadwian]

The explanation for what Ohm's law is is also plastered on dozens if not hundreds of websites on the Internet. If people have such preconceptions without trying to find the information themselves out we can't force feed them the knowledge, they have to be willing to get it themselves. Electronics is NOT as difficult as most people believe if you start with a good website or book that contains the fundamentals, of which there are a great many to be had for free.

 

[Hero999]

You've missed the point.

It's true that there are 100s of Ohm's law tutorials plastered all over the internet but both you've missed the OP's point. Many nubies don't fully understand the practical implications of Ohm's law so they ask all sorts of silly questions:

"My 5V MCU circuit only needs 20mA, will it be damaged by powering it from an LM7805 regulator which will supply 1A?"

"I have a radio which is rated at 6V 500mA but my battery says 6V 7Ah, will it damage the radio?"

And so on and so on.

Another classic is the maximum voltage/current ratings on components:

"My circuit is run from a 9V battery and requires a 10µF capacitor, can I use a 50V capacitor?"

"I need to switch a 12V 1A motor with a switch that says 50VDC 10A on it; will it work?"

etc.

There needs to be an FAQ that covers stupid questions like this.

Fair enough, most people won't read it, but we can at least post a link to it, everytime someone asks a silly question like that.

 

[Sceadwian]

It's easier and simpler to explain it than it is to post a link. It's not even really a problem with the understanding of Ohm's law, it's understanding of what power supply capacity means. Almost no devices list a nominal resistance value at it's rated voltage so Ohms law isn't even applicable. It can be explained in one simple sentance. The voltage of the power supply must be the same as the device that will be plugged into it, and the current capacity of the power supply must be equal to or greater than (preferably at least 25% more) than that typically drawn by the load.

 

[Sceadwian]

Battery capacity is a more complicated subject because discharge curves an amphour ratings are based on specific load ratings. It's not a simple subject and depends completely on specific battery in use and it's condition, which very from maker to maker. General guidelines can be made for simple NiMH NiCad and Lead Acid packs however these general guidelines are just that, general. MANY users asking questions like this are trying to reuse scrap batteries so the answer isn't as simple as a basic calculation.

 

[Hero999]

Just another thought, even with power supplies, it's not that simple because some unregulated power supplies give nearly double the voltage when unloaded.

https://www.electro-tech-online.com/threads/wall-adapter-says-9v-dc-but-measures-at-17v.106045/

 

[Mickster]

There needs to be an FAQ that covers stupid questions like this.

Fair enough, most people won't read it, but we can at least post a link to it, everytime someone asks a silly question like that.

That is the problem though.....the reluctance to actually research something before asking for further help.

There are many members here with a vast amount of knowlege, literally scouring the forum daily in the event they can pass on something of use to others - you all know who you are and can easily recognise others doing the same, so naming names is pointless and someone will probably get left out...

Your free time is valuable not only unto yourself, but also to those actually in need of further help, without constantly having to rehash the same things over and over again for those unwilling to help themselves.

It is not unreasonable to expect that someone asking questions has done a little groundwork first, but perhaps failed to fully understand a particular point, before asking for help.

Directing a person to a well-written FAQ should give them an opportunity for enlightenment and suggest terms for further research, rather than spoon feed them specifics via a personal post which rarely gets acknowleged.....

However...it's your own free time and yours to spend however you choose.

 

[bychon]

About that earlier Ohm's Law attempt...
Holy frijoles! I never saw such a load of trying to overcomplicate a formula that anybody with 3 days in electronics should know.
The point is trying to help noobies, not the calculus of semiconductor junctions, but I see that there are people who will INEVITABLY turn a 3 letter equasion into a congressional hearing, and that is just as non-productive as not knowing Ohm's Law.

 

[RodJac]

G'day all, I am a new person on this particular system. I am also an "old" hand in electronics and see that there are also quite a few people here who know what they are talking about. One reply on this thread made a mistake, quite accidently. It referred to a silly question. There are really no silly questions, people who are new to the game ask questions that SEEM silly to experienced people.
I like the answer from scedwien?, which states that we MUST show patience and answer as best we can.
I will be glad to help any 'newbie' with answers to what must seem mountainous questions. 'I was a newbie too'.
Cheers all
Rod

 

[Mikebits]

Recent exchange prompts me to discuss the fact that about once a day, we get a post by a person who thinks that if a battery is rated at 10 amp-hours, anything connected will have 10 amps forced through it. Other Person suggested a FAQ be made available for noobies that don't know Ohm's Law. I very much agree and wish I could refer posters to a FAQ or Tutorial about E=IR and P=IE. It would have to be written in very, very basic language. I would happily leave that job to someone else.

Well, if you are willing to write it up, I can add it to the New to electronics FAQ.

 

[RodJac]

G'day all,
Ohm's law is NOT rocket science. Newbies only need remember the formula, and how to relate to it. You need 2 facts only: Either AMPS and VOLTS or OHMS. The formula that has been mentioned before is I=E/R Where I is the current in AMPS. E (sometimes called V, which is exactly the same thing) is the voltage across the circuit measured in VOLTS. Lastly, is R, this is the circuit resistance in OHMS.
The best way to remember the formula is to draw an equalateral triangle. Draw a line horizontally across the triangle about half way down.
In the bottom section, draw a vertical line from the horizontal line to the base of the triangle.
Now you have 3 seperate compartments. In the top compartment, label it E (or V if you wish)
In the bottom left compartment, label it I.
In the bottom right compartment, label it R.
now looking at your chart you can see the 3 formulae.
I at the left = E on the top, over or divided by, R on the bottom right.
E on the top line = I at the bottom left multiplied by R on the bottom right.
R on the bottom right = E on the top divided by I on the bottom left.
Simple hey!!
If there is a need to go into capacity (of a component, EG Battery switch rating, Etc.) versus the circuits needs, then drop me a line and I will try to explain that too.
If this seems too simplistic, remember, none of us were BORN with electronics ingrained.

Regards,
Rod

 

[Mikebits]

I just remember the formula E=IR then using simple algebra I can solve for any variable. No need for any memory aids such as the triangle thing.

 

[RodJac]

I just remember the formula E=IR then using simple algebra I can solve for any variable. No need for any memory aids such as the triangle thing.

G'day Mikebits,
my post was designed to help all newbies, I didn't mean to insult anyone.
Kind regards,
Rod

 

[Sceadwian]

RodJac, you also seem to have no actually read the original post =) While the topic of this thread says "Make Ohm's Law FAQ' available, the example given by the poster has nothing whatsoever to do with Ohm's law directly, it's a problem many people have problems understanding what the values written on power supplies and devices mean.

 

[RodJac]

G'day Sceadwian,
I confess that I took the header too literally. At the end of my mailing, I also said I was prepared to delve into the difference between "Capacity and Ratings". It seems that instead of trying to help others, people are more interested in "flaming" those who try.
Sorry I misread the situation. If I am doing wrong by this group, please tell me and I will get out
Rod

 

[Sceadwian]

You're willing to say sorry and seem perfectly reasonable to me =) That's more than I can say about a few users here =) Relax and enjoy the forums, don't take anything too personally, and as long as you're polite and reasonable don't worry about offending too much.

 

[bychon]

I have 7 pages written in 3 categories. I wish to submit them to somebody who makes decisions about this forum. Upon examining them, the reviewer may use them, ignore them, modofy them, delete them, laugh at them, or whatever else he/she feels inclined to do. They are written in Open Office. That can be changed.

Please respond with link or address or whatever required for me to send these pages.

 

[Mikebits]

I have 7 pages written in 3 categories. I wish to submit them to somebody who makes decisions about this forum. Upon examining them, the reviewer may use them, ignore them, modofy them, delete them, laugh at them, or whatever else he/she feels inclined to do. They are written in Open Office. That can be changed.

Please respond with link or address or whatever required for me to send these pages.

Maybe you can post in the articles section on this forum and I can add a link to it in the FAQ. Just a thought. I can't see adding a 7 page article to the FAQ as that may make it too text heavy and may lose the readers interest. But a link to your article sounds workable. Well just consider it.

 

[bychon]

I'm having trouble finding the "articles" section. Could you please point me in the right direction?