# Find turns !!!

#### k31453

Joined May 7, 2013
54
Okay I got this :

i dont have inductance value..
this all i got and i dont know how to do this ??

I tried to get inductance then turns but it doesnt workout

#### MrChips

Joined Oct 2, 2009
21,399
Well then you would need a formula for the inductance of a coil of given length, diameter, number of turns and magnetic permeability.

#### k31453

Joined May 7, 2013
54
Well then you would need a formula for the inductance of a coil of given length, diameter, number of turns and magnetic permeability.
Yeah but which one? ..cause i checked of dozens of that ?

i got one answer which give me 3 turns which is ridiculous !!!!

also where do i find magnetic permeability.?

#### Ron H

Joined Apr 14, 2005
7,014
Yeah but which one? ..cause i checked of dozens of that ?

i got one answer which give me 3 turns which is ridiculous !!!!

also where do i find magnetic permeability.?
What value did you get for the inductance? That should be pretty easy.

All of the sites listed below have the same equation for the inductance of a solenoid. It is the one I have always used.
These are the first four Google hits I got when I searched for "solenoid inductance".

http://en.wikipedia.org/wiki/Solenoid
http://hyperphysics.phy-astr.gsu.edu/hbase/electric/indsol.html
http://faculty.wwu.edu/vawter/PhysicsNet/Topics/Inductance/Solenoid.html
http://www.ittc.ku.edu/~jstiles/220/handouts/Example The Inductance of a Solenoid.pdf

You have to do some searching to find the permeability of air, and you have to be careful about the units of the dimensions.
After I calculated the inductance, I calculated the number of turns N, using the equation (after solving it for N). As a check, I then plugged that number into the calculator on the first site listed, and got the same inductance.

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#### WBahn

Joined Mar 31, 2012
25,930
You've told us that you've found stuff or that you've calculated stuff, but you need to SHOW us your work so that we can see what you are doing right and what you aren't. Otherwise we are just guessing and playing mindreader.

#### Bernard

Joined Aug 7, 2008
5,562
I believe as used in most formulas, permiabiality is relative, where standard is a vacuum =1, air not far away.
Why does seem 3 turns seem out of line, remember that you are at the top end of the FM radio range.

#### Ron H

Joined Apr 14, 2005
7,014
I believe as used in most formulas, permiabiality is relative, where standard is a vacuum =1, air not far away.
Why does seem 3 turns seem out of line, remember that you are at the top end of the FM radio range.
Using the permeability of air (not relative) in the equation, I got a few turns, but it was considerably more than 3.

#### Bernard

Joined Aug 7, 2008
5,562
Using Allied's Coil Winding Data , L = about 2/10 μH, giving around 8 turns, give or take.

#### Ron H

Joined Apr 14, 2005
7,014
Using Allied's Coil Winding Data , L = about 2/10 μH, giving around 8 turns, give or take.
The equation I used gave me 7.4368 turns.

#### k31453

Joined May 7, 2013
54
The equation I used gave me 7.4368 turns.
i know u can use f = 1/sqrt(LC) for find L then which equation you use.

thanks

#### Ron H

Joined Apr 14, 2005
7,014
i know u can use f = 1/sqrt(LC) for find L then which equation you use.

thanks
No, f=1/(2*pi*√(LC)).
For turns, see post #4.