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# Algebra help needed...

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#### captainkirksdog

##### Member
Hi,
I've gone brain-dead about some simple algebra. This is the formula for air-core coils:
N^2=L(3a+9b+10c)/0.2a^2
Where:
N=Number of turns
L=inductance in microhenries
a=wire diameter in inches + form diameter
b=length of winding in inches
c=wire diameter in inches
Now I can easily solve for N, but what if I know N and need to solve for L? In other words, I have several unmarked coils that I would like to know the inductance of. Since I don't have an accurate inductance meter, I was hoping to calculate their values. Can someone show me the way to do this? Thanks.

Simple manipulation brings me to :

L=N^2*0.2a^2/(3a+9b+10c)

HTH Chip

A bit of formatting.....if you are going to solve this equation on dumb computer.
L = (N^2)*(0.2a^2)/(3a+9b+10c)

+ a bit more
L = (N²)*(0.2a²)/(3a+9b+10c)

Ok :wink:

Yes I did.

Chippie said:
Simple manipulation brings me to :

L=N^2*0.2a^2/(3a+9b+10c)

HTH Chip

so my answer not sufficient ? :cry:

I kept it in simple terms as per the original thread to avoid confusion

Hi,
At the risk of sounding like a doofus, can one of you show me how you got this answer? Where did I go wrong with this:
L=N^2(3a+9b+10c)/0.2a^2

Let's take a simpler example:

N=A*B/C, and you want to solve for A.

You can multiply (or divide) both sides of an equation by the same amount, and the equality is unchanged. So...

Multiply both sides by C: N*C=A*B

Divide both sides of this equation by B:

N*C/B=A, or of course, A=N*C/B

Apply these principles to your original equation. You'll get the same result as the other posters did. If you don't, you should abandon electronics in favor of gardening. :wink:

damn pc!!

plz delete this post.......

Ron H said:
You'll get the same result as the other posters did. If you don't, you should abandon electronics in favor of gardening. :wink:

Encouraging words...... :!:

This forum is all about helping each other....although at times I wonder

Thanks guys! I remember now. I was MOVING the desired element rather than EXTRACTING it. At least that's the way my old physics teacher said it. I had the same problem back then. Maybe I SHOULD take up gardening, hmmmm.......

Chippie said:
Ron H said:
You'll get the same result as the other posters did. If you don't, you should abandon electronics in favor of gardening. :wink:

Encouraging words...... :!:

This forum is all about helping each other....although at times I wonder

Hmm.... I thought the emoticon :wink: was an indication that I was being facetious.

In defense of Ron H.

For those of you who don't know "Ron H.", allow me to introduce him to you. He is a very technically-knowledgeable person who is always right. Well, there was the one time that he thought he was wrong, but ....

Anyway, he's a wiser older bird just a few years older and a bit smarter than me (making me simply a wise old bird) who, also like me, has a very dry sense of humor. So, Ron and I get along quite nicely because we understand each other!

Simply put, always remember the "4E rule" and know that whatever Ron writes is written with the intent to educate, edify, encourage and entertain ... unless you've gone out of your way to hack him off or belittle another poster, where he will then modify the manner in which he entertains. He deserves our thanks and respect, for I have often witnessed him helping folks out of really messy electronic situations. His signature line should say, " 'Electronics Newbie' indeed -- give me 30 minutes and I'll design you a 4GB dynamic RAM that'll run circles around anything the Japanese can offer."

Dean

Ron, my address may be changing in the near future, so send that money you promised as quickly as possible.

Geez, Dean, I already had a big head (7 5/8). None of my hats will fit me now. I'm not really the wizard you make me out to be. I just know when to keep my mouth shut. That's why I don't post on most threads on the various electronics forums.
We belong to a mutual admiration society, to coin a phrase. I am always amazed at the breadth of your knowledge. Of course, I notice that you also disappear from time to time.

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