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[itex]\pi[/itex]*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*[itex]\pi[/itex])/(B1*R) so H= -(6.61R/[itex]\pi[/itex]) But now I'm stuck, and I don't know if my work so far is even right.