# Magnetic Fields from Currents in a Wire and a Cylindrical Shell

1. Mar 27, 2013

1. The problem statement, all variables and given/known data[/b]

A solid cylindrical conducting shell of inner radius a = 4.9 cm and outer radius b = 6.1 cm has its axis aligned with the z-axis as shown. It carries a uniformly distributed current I2 = 7.4 A in the positive z-direction. An inifinte conducting wire is located along the z-axis and carries a current I1 = 2.8 A in the negative z-direction.https://www.smartphysics.com/Content/Media/Images/EM/15/h15_cylinders.png [Broken]

What is ∫B$\bullet$dl where the integral is taken along the dotted path shown in the figure above: first from point P to point R at (x,y) = (0.707d, 0.707d), and then to point S at (x,y) = (0.6d, 0.6d).

2. Relevant equations

Ampere's Law

3. The attempt at a solution

Not real sure how to start this question. i know the integral =4*pi*10^-7* I(enclosed) are we suppose to find the charge density of the outer circle?

Last edited by a moderator: May 6, 2017
2. Mar 27, 2013

### Sunil Simha

Charge density has no use in this problem. You could start by finding out how much current would be enclosed by that loop if it were complete.

3. Mar 27, 2013

Complete as in having a circle having radius d?

4. Mar 27, 2013

### Sunil Simha

Yes that is the loop that I meant. Once you get that, what would be the symmetry of the magnetic field along it? how could you exploit it to get the desired result?

Sorry for replying late. There was apparently some internal server error on PF and I couldn't log in early.