How Does Current Direction Affect Magnetic Field in a Coaxial Cable?

[Master J]

A coaxial cable has a conductor lying at the centre of a thin walled cylindrical conductor. These conductors are separated by a plastic dielectric, and they carry equal current in opposite directions.

The radii and current are given, and I must find the magnitude and direction of magnetic field.


I'm generally good with stuff like this and have a decent grasp of the physics. I'm just unsure how to approach this question. Whats the best way of going about it? Any nudges in the right direction??

Thanks!

 

[NateD]

The first thing to do is to calculate the magnetic field due to each conductor. This can be done using Biot-Savart law: B = (mu_0*I)/(2*pi*r) Where mu_0 is the permeability of free space, I is the current and r is the distance from the conductor. Then, you need to add up these two fields as vector components for the final magnetic field. The magnitude of the total field will be equal to the square root of their sum of squares, while the direction can be found by looking at the sign of each component.