remember a formula

Learn just one formula such as V=IR and rearrange terms mathematically as needed. No escaping the math if you want this field.

Pedantic mode on. :-) You have to learn _two_ equations, actually.

V=I*R (Volt=Amp*Ohm) P=U*I (Watt=Volt*Amp)

Then learn how to re-arrange these equations as needed for the problem at hand, and use a calculator to get the result.

The art of re-arranging equations is called algebra, and you need some basic knowledge and experience in this.

An alternative is to use a visual diagram like the ones I have put on a web site

Click on the two .jpg files at the bottom of the list, save them to hard disk. Can be distributed freely.

--
Roger J.

Can someone sum up the top couple of rules of algebra for him? How about something like: 'An equation has an expression on each side of the equal sign. To solve the equation for any of the variables, you need to get that variable over to the left side of the equal sign. To eliminate a variable on one side, multiply both sides of the equation by the inverse of that variable. This doesnt change the equality, because you are multiplying both sides by the same number.' Is this the necessary and sufficient information needed to solve ohms law for 3 variables?

Hi, You are asking for a method to' remember' something and you are being given answers on how to' learn' something. I would suggest that you take the advice that says 'learn' algebra. If you learn the relationship that is generically referred to as "Ohm's Law" and learn the algebra to solve for all variables you will be in far better shape when the formulae get more complicated. Regards, Tom

If you going to learn P=VI rather learn P=VIcos(Phi) where Phi is the phase between V and I.

I use three rules:

1. If you do something on one side of the equal sign, you must do the same thing on the other.

1. Anything divided by itself equals 1.

2. Anything multiplied by 1 is unchanged, so the "1" can be discarded.

I've been working in electronics for some 40 years, and have no idea what the "P.I.R.E. wheel" is - I just remember E = IR and P=EI, and shuffle things around as needed. The same "shuffling" rules apply to any simple equation.

--
Peter Bennett VE7CEI 
email: peterbb4 (at) interchange.ubc.ca        
GPS and NMEA info and programs: http://vancouver-webpages.com/peter/index.html 
Newsgroup new user info: http://vancouver-webpages.com/nnq

Thanks, I know basic high school algebra, but I just never understood how to apply it to real world problems. I keep reading my electrical book on that it says "Current is directly proportional to voltage" and "Current is inversely proportional to resistance" and then I look at the P.I.R.E. wheel, trying to remember the whole wheel just by remembering those statements and some algebra. I'm looking at it like a puzzle and noticing some patterns like, that the power formulas you have to square or square root to find an answer, so I can see that proportional and inversely proportional part. I'm trying to figure out how they got something like this "I = E/R" from that statement, looking at that formula, thinking "I" is proportional to "E" and "I" is inversely proportional "R", and I'm thinking why did they divide?. I'm racking my mind and I know this is a simple basic DC formula compared to other electrical formulas like, the AC ones.

Exactly! And like most technical people, I don't give a rats ass about being PC with the resistor color code mnemonic.

I can add some to your text above.

You can do anything to an equation as long as you do it to both sides equally, the equation is still valid. (an exception is dividing by zero, which gives meaningless results)

The methods you can use to isolate one variable on one side are addition, subtraction, multiplication, division, inverting, squaring, square root, substitution, etc..

Somebody who does not know these methods should take some time to learn basic algebra, especially equation solving.

--
Roger J.

Here is such a wheel, if you are curious.

Here is a lesson in simple equation solving algebra

An online equation solver, for really lazy people :-)

It is incredible how much stuff you can find on the web today, you only need to put together the right search words.

More advanced lessons in algebra. Ask dr Math!

--
Roger J.

Another definitions of "ohms" is volts per ampere. So, for any fixed resistance, the ratio of volts divided by amperes (volts per ampere) equals the value of the resistance. So resistance is the constant of proportionality that relates volts to amperes. 100 ohms means that the voltage is always 100 times the amperes.

The basic definition of resistance R=E/I (ohms equals volts per ampere) can be rearranged to I=E/R or E=I*R.

The second basic formula on those wheels is P=E*I. But you can substitute I*R for E (from the above rearrangement of R=E/I) to get P=I*I*R or substitute E/R for I to get P=E*E/R

That is all there is on that wheel.

The term "inverse" means 1/whatever just as the term "per" means "for every". When someone says "percent" they mean "for every 100". One cent is 1 of

100. As some smart man has said, "Words have meanings". Now if he could only pronounce "nuclear" properly.

At this point, it might help to look at the water pipe model. Voltage, or "electromotive force" is pressure, current is the flow rate, and resistance is how hard you have to push to get the water to go through the pipe. A skinny pipe has more resistance than a fat one.

The model breaks down when the pipe breaks, and all of your water falls out on the ground - that's the opposite of what happens with a broken wire; short circuit to "ground" would have that effect. ;-)

Cheers! Rich

And it's so cheap to do these days.

--
Best Regards,
Mike

Not to mention very patient or willing to accept no answer at all.

solve x^3 - x^2 -y = 0 for x :)

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Best Regards,
Mike

wheel.

Here's a non-algebra method of deriving the 12 equations of the P.I.R.E wheel from just 2 "triangle" diagrams. So, if you can remember the two triangle diagrams, you can quickly come up with the whole wheel.

First, there's the P = IE triangle:

P

------ I | E

By covering up either P, I, or E with your finger, what remains will remind you of the formula for what you covered up:

P (covered) = I * E I (covered) = P / E E (covered) = P / I

For the remaining 9 formulas of the wheel, start with the E = IR triangle:

E

----- I | R

By covering up either E, I, or R with your finger, what remains will remind you of the formula for what you covered up:

E (covered) = I * R I (covered) = E / R R (covered) = E / I

Now take the same E = IR triangle, and multiply both the top and left side by I. You now get:

E * I

----------- I * I | R

Because P = E * I (from the first triangle), and I * I = I^2 (that is, I squared), you can rewrite this as:

P

--------- I^2 | R

By covering up either P, I^2, or R with your finger, what remains will remind you of the formula for what you covered up:

P (covered ) = I^2 * R I^2 (covered) = P / R, so I = square root of (P / R) R (covered) = P / I^2

Now go back to the E = IR triangle, but this time multiply both the top and left side by E. This time you get:

E*E

--------- E*I | R

This is the same as:

E^2

---------- P | R

By covering up either E^2, P, or R with your finger, what remains will remind you of the formula for what you covered up:

E^2 (covered) = P * R, so E = square root of (P * R) P (covered) = E^2 / R R (covered) = E^2 / P

You've now developed all 12 equations of the P.I.R.E. wheel.

--- Wayne

Perhaps i'm nuts to even attempt to fiddle with electronics, because my math skills are not so great. I'm 10 years out of HS, and at the time i programmed my computer to do my homework for me :-(

Yeah i know that was stupid. I'm paying for it now.

Re-teaching myself Algebra is obviously a requirement, but will I need to teach myself anything like Calculus? Trigonometry?

I know that "electronics" is vague, and different parts of it have different skill requirements, so take in mind that i'm mainly interested in the musical instrument amplification/effects end of audio equipment. Logic gates and processing signals like that isn't so exciting for me (at least not now)- programming in C has kinda burned me out of that sort of thing... :-P

I always consider night classes at the local community college but i'm always afraid i'd bomb out of any placement tests and have to start math courses from the 7th grade or something. (Which if that's the case, then the test worked, and it is pointing me in the right direction and telling me exactly what I need to do).

Although, playing around with some algebra equations i've dug up online, i'm surprising myself on some of the things i *do* remember....

Thanks for any suggestions, even if they're wrong :oP

-phaeton, Smoking Si since 1994

You can find a lot of help on the web.

I used the search words free algebra lesson and found a lot of free resources.

This lesson in basic algebra, for example:

You can probably find useful books in your local library too.

--
Roger J.