using ohms law formulas

Heres a handy formula to
FIND a needed unknown resistance ( R2) to use  in parallel

with a on hand resistor value ( R1)

in order to make a desired (required) value. (RT)

R1 = On hand resistor value
RT = Required total resistance

R2 = Resistor to find to get to total required resistance

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

R2 =  R1 X RT / R1 - RT

I know that, but what I was refering to was why use I vs/vs A?

Quoting you: ". . .I don't know the whys of using the letter A for amps"

Stands for, of course, amperes, named in honor of Andre Marie Ampere, 1775-1836. From Gernsback's Radio Encyclopedia, "Noted for his researches in the field of electro-dynamics."

When some of these designations were made it was to make it easy by relation to letters to make the formulas less cumbersome. The letter I was the first selected for current, I don't the whys of using the letter A for amps, but to continue, the letter I was also going to be used for impedance but it was taken for the use of current, so the letter Z was adopted instead.

Lord Kelvin may or may not had some influence on that decision. I found out about 2 years ago That He is my great great great (great?) cousin or grandfather twice removed. Kinda proud of that! I havn't done much research but one of the family web sights sent me a notice about it.

Well, I'll be darned. . . !

The Designation (I) means

Intensity

of current in Amperes.

Re Ohm's law, if E stands for voltage (Electromotive force) and R stands for, more obviously, Resistance, then what word that begins with I means current? This is not a quiz; I've never understood why the letter I represents current, when it's clear why E and R are used.

Heres a graph for wire
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I have a few also, after we started using calculators and computers in the shop the slide rules just started to collect dust, so I salvaged them from collecting unwanted dust bunnies, still have fun showing them to the young shavers occasionally. I had a circular rule once made out of aluminum, never figured out what happened to it. I would like to get an electronics slide rule, but not willing to pay those prices.

I remember using a parallel calculator nomograph that was fun to use.
I should see if I can post it

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The two outside sets of numbers represent the resistor values used. The center lined between the two sets is the resultant value of the two parallel resistors. So looking at the values of 56 ohms and 42 ohms the resultant value is approximately 24 Ohms

I've often wondered about the programmable ones, but never got one.

As a reverse to this, while digging through a box in the attic, I found my old slide rule, and for the life of me I can't remember how to use the darn thing. It's only been 43 years since I last used it. When I got out of trade school it got put away as I didn't want it getting banged up in a tool box with my metal working gear.

Dunno why, but I want to learn it again just for fun.

Bob

I have several calculators, Most are Hewlett Packards and use RPN logic. I find them faster. One is the HP 48, and is programmable, has plug-ins and several libraries. The reciprocal function is very useful. Also another is vectoring for determining Phase.

I have two that I can change between Algebraic and RPN which is nice at times.

When calculator shopping I always make sure it has the 1/x function.

A definite must for resistors in parallel and caps in series. I've found that not all of them have that function.

Cheers, Bob

Ohms law is used to calculate resistance, current and voltage.
Several methods are use to obtain the desired results.
To find Voltage in a formula the expression used is the symbol for voltage = E
E = I X R

To find current in a formula the expression used is the symbol for current = I
I = E / R

To find resistance in a formula the expression used is the symbol for resistance = R
R = E / I


So lets find the voltage in a simple circuit.

The two knowns are the resistance and the current.
The resistance equals 1000 ohms and the current is 100 milliamps.

So enter the following numbers in this order :

"1000"
" Times (or X)"
" .1"
" = "
The answer would be ?
Try it.
Answer is 100 so it's 100 volts