Multiple choice question on finding magnetic field

[RoboNerd]

Homework Statement

E is the "right answer"

Homework Equations

B around a long wire = mu * I / [2 * pi * r]

The Attempt at a Solution

OK. I know that the magnetic field lines will travel in a clockwise direction around the wire from the viewer's orientation with the current going away from the viewer due to the right hand rule.

This means that the magnetic field created by the left wire will go into the negative y direction, and the magnetic field created by the right wire will go in the negative x direction.

Thus, I can get the magnitude of the net magnetic field at the origin by getting the two magnetic field vectors in the negative x and y directions and then applying pythagorean theorem.

Off I go. YAY!

B field in negative x direction caused by the left wire is going to be: mu0 * I / [2 * pi * 3]
B field in a negative y direction caused by the right wire is going to be: mu0 * I / [2 * pi * 4]

So magnitude of net magnetic field = sqrt ( B field in negative x direction^2 + B field in negative y direction^2 ) =
[5 * mu0 * I] / [ 24 * pi].

This is not what answer E, "the official right answer" is.

Could anyone please provide some input as to what went wrong?

Thanks in advance for the help!

 

[TSny]

Your answer looks correct to me. I'm not sure what the symbol ##f_0## means in the answers that were provided.

 

[RoboNerd]

They mean Mu0 in that answer.

Thanks for helping!