Posted by **Mary** on Thursday, September 27, 2007 at 11:06pm.

A piece of copper wire has a resistance per unit length of 5.95 10-3 /m. The wire is wound into a thin, flat coil of many turns that has a radius of 0.200 m. The ends of the wire are connected to a 12.0 V battery. Find the magnetic field strength at the center of the coil.

In this question do I use the following formula:

F = /q0/v(permeability of free space x I / 2piR) sin theta

- Physics -
**drwls**, Friday, September 28, 2007 at 11:03am
The field at the center is proportional to the number of turns, N, but the current is inversely proportional to then number of turns (because increasing N increases the resistance). Therefore N cancels out.

B = mu*N I /(2r)

(For a reference to that formula, see (Broken Link Removed)

r is the loop radius; R is the total resistance of all N turns

I = V/R

R = (resistance per length)* 2 N pi r

I = V/((resistance per length)* 2 N pi r)

B = mu*V/((resistance per length)* 4 pi r^2)

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