1. The problem statement, all variables and given/known data A long straight wire of radius R carrying a current I has a circular portion of radius a cut out at a distance d from the center, as shown in the picture. Find the magnetic field inside the cut-out portion. 2. Relevant equations magnetic field equation (I can't write it here) 3. The attempt at a solution I couldn't integrate the magnetic field directly. So I tried many tricks to solve this problem. I tried to reduce this into two different straight wires and worked out geometry but couldn't figure it out. If there is no cavity, it's very simple problem. But since I need to find the magnetic field inside the cavity, I need something else.