# Find turns !!!

Discussion in 'Homework Help' started by k31453, May 16, 2013.

1. ### k31453 Thread Starter Member

May 7, 2013
54
0
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

2. ### MrChips Moderator

Oct 2, 2009
12,636
3,454
Well then you would need a formula for the inductance of a coil of given length, diameter, number of turns and magnetic permeability.

3. ### k31453 Thread Starter Member

May 7, 2013
54
0
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.?

4. ### Ron H AAC Fanatic!

Apr 14, 2005
7,050
657
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.

Last edited: May 17, 2013
5. ### WBahn Moderator

Mar 31, 2012
18,087
4,917
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.

6. ### Bernard AAC Fanatic!

Aug 7, 2008
4,240
414
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.

7. ### Ron H AAC Fanatic!

Apr 14, 2005
7,050
657
Using the permeability of air (not relative) in the equation, I got a few turns, but it was considerably more than 3.

8. ### Bernard AAC Fanatic!

Aug 7, 2008
4,240
414
Using Allied's Coil Winding Data , L = about 2/10 μH, giving around 8 turns, give or take.

Apr 5, 2008
15,804
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10. ### Ron H AAC Fanatic!

Apr 14, 2005
7,050
657
The equation I used gave me 7.4368 turns.

11. ### k31453 Thread Starter Member

May 7, 2013
54
0
i know u can use f = 1/sqrt(LC) for find L then which equation you use.

thanks

12. ### Ron H AAC Fanatic!

Apr 14, 2005
7,050
657
No, f=1/(2*pi*√(LC)).
For turns, see post #4.