# Magnetic field at a point due to two wires and a solenoid.

1. Nov 23, 2011

### TimeToShine

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?