1. The problem statement, all variables and given/known data Given an infinite long (in the z-direction), with width 2b in the y-direction and no thickness in the x-direction. There is a current with density J in the z-direction. Calculate the magnetic field on the y axis if |y| > b. 2. Relevant equations Amperes law: ∫B*dS = μ0*I 3. The attempt at a solution My first thought was that the strip is build out of infinite wires, so according to the right hand rule the magnetic field would be in the negative x-direction for y > b and the positive x-direction for y < -b. But I see no possibility to choose a suiting ampere path.