1. The problem statement, all variables and given/known data The point p is located at (3,1,2). An infinitely long straight wire passes through the points (0,0,0) and (0;1;0) and carries a current of a A in the positive y direction. A finite length of wire carries a current of b A from (2,0,0) to (2,0,0). An semi-infinite solenoid of n turns per metre starts at p, extends in the positive z direction towards infinity and carries a current c A flowing clockwise when viewed axially from p. I have to find the magnetic field at P due to the three sources. 2. Relevant equations Biot savart law, amperes law. 3. The attempt at a solution Well, I've used the formula for the magnetic field B at a point due to an infinitely long current carrying conductor: B = u0.I/(2.pi.R) For the solenoid, would I be right in assuming that once I use the formula B = u0.N.I to get the magnetic field in the solenoid I can then treat it as a wire of infinite length with current C, similar to the first wire? Since the solenoid starts at P is the magnetic field at P just equal to the magnetic field obtained from the above formula? I'm not sure how to approach the finite length wire. I tried to find the shortest distance between it and P and then use the same formula as the infinite length wire but it gave a strange answer. Once I get the three answers I just use superposition and add the results I presume. Also, on another note, it says on the paper as a "hint" that no finite length wire can exist in isolation. Can anyone tell me why this is? thanks in advance.