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

  • #1

Homework Statement


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?



Homework Equations



Bio-Savart Law

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?
 

Answers and Replies

  • #2
rl.bhat
Homework Helper
4,433
7


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.
 

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