# Homework Help: Coaxial cable with unequal currents

1. Apr 19, 2010

### satchmo05

1. The problem statement, all variables and given/known data
I just have a question concerning an unbalanced coaxial cable. By unbalanced, I mean that the inner and outer currents are not equal magnitudes of the opposite direction of each other. My homework problem has an inner current of +100[mA] and an outer current of 90[mA] in the opposite direction. My question is regarding the form of the answer.

2. Relevant equations
Cylindrically symmetric current distribution - able to use Ampere's Law here!
Bdl = μo*Ienc

3. The attempt at a solution
Implementing the cylindrically symmetric current distribution, the left side of the equation ends up being:
2∏ρ*BФ(ρ) = ...
However, the right side of the equation is where I am having trouble. Would the enclosed current be equal to +10[mA] (100-90[mA]), or something else? An enclosed current of 10[mA] to me makes sense, because if I were an observer looking at the cable, I would only see a magnetic field rotating in the phi-direction, with a current of 10[mA] flowing up the z-axis. I appreciate all help in advance! Thank you much!

2. Apr 19, 2010

### Antiphon

You are correct.