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: Why do the upper and lower potions cancel the magnetic field?

  1. Mar 23, 2010 #1
    1. The problem statement, all variables and given/known data
    Referring to the magnetic field in a solenoid:

    "The field at exterior points is weak because the field due to current elements on the upper potions tends to cancel the field due to current elements on the lower portions"

    Why do the upper and lower potions cancel the magnetic field?



    2. Relevant equations

    Bio-Savart Law

    3. The attempt at a solution

    This is suppose to to explain why the magnetic field outside a solenoid is zero, but I am not sure why. When I draw the components of the current creating the magnetic field outside a solenoid, they do not cancel out. Is my reasoning incorrect?
     
  2. jcsd
  3. Mar 24, 2010 #2

    rl.bhat

    User Avatar
    Homework Helper

    Re: Solenoid

    In a coil, if the current in the upper current element on the top is going into the page, the field in the exterior point is towards right. The current in the lower current element is coming out of the page. The field due to this current element at the same exterior point is towards left. So the net field at that point is reduced.
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook