# Homework Help: Net Magnetic Field at the Center of a Loop and X Distance Away From a Wire

1. Mar 21, 2012

### BornSurvivor

1. The problem statement, all variables and given/known data
https://fbcdn-sphotos-a.akamaihd.net/hphotos-ak-prn1/553004_1959186995753_1725123128_934768_456680196_n.jpg [Broken]
In case the words are too small:
I2= 6.61I1
The net magnetic field at center of loop is 0.
I'm looking for the radius of the loop

2. Relevant equations
for straight wire: B=(u0*I)/(2$\pi$*r)
for loop: B= (u0*I)/(2*r)

3. The attempt at a solution
So, since the two magnetic fields are perpendicular to each other: √(B12+B22)=0
I tried to find H in terms of R by using the right hand rule. I2/I1=(B2*H*$\pi$)/(B1*R) so H= -(6.61R/$\pi$)
But now I'm stuck, and I don't know if my work so far is even right.

Last edited by a moderator: May 5, 2017
2. Mar 22, 2012

### tiny-tim

Hi BornSurvivor!

(pleeeeeease don't post such wide images! )
No, a loop current's magnetic field goes along the axis of the loop,

and a straight line current's magnetic field goes in loops around the line.