1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Magnetic field at a point due to two wires and a solenoid.

  1. Nov 23, 2011 #1
    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.
  2. jcsd
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Can you offer guidance or do you also need help?
Draft saved Draft deleted