Finding the diameter of a coil.

[cds5615]

Homework Statement

You have a 1.2-m-long copper wire. You want to make an N-turn current loop that generates a 0.60 mT magnetic field at the center when the current is 1.5 A. You must use the entire wire.

Homework Equations

What will be the diameter of your coil?

The Attempt at a Solution

I tried applying this formula d = sqrt ( (mu*L*I/pi*B)) and keep getting a really small number =0.000021 m

What am I missing here??

 

[Rake-MC]

What was the original formula? Name of it?

 

[cds5615]

I actually just got it from a classmate, him and his friend were both able to get to the answer from that equation.

I tried using B= mu*(N/L)*I but you don't end up with a numerical value when solving for d. There must be a way to find the answer with another method...

 

[Rake-MC]

Ahhh I see, well I'll s how you how to do it. Use Ampere's law. BL = IN\mu_0

It will yield the correct answer, and I can see whoever wrote the question planned it very well.

 

[cds5615]

But I am solving for diameter. How can I apply that equation?

 

[Rake-MC]

Well.. You know everything except for N (number of turns).
Once you've found how many turns you have divide the length of the coil by N. That will clearly give you the circumference of each turn (provided they are uniform).