Finding distance r for zero net magnetic field from loop and straight wire

[GingerBread27]

An infinitely long wire is formed as in the diagram on your assignment. It is formed so that it has a circular portion of R = 50.0 cm and the straight portion is located at a distance r from the center of the circular portion. Find r (in cm) such that the net magnetic field at the center of the circular portion is zero.

Ok so I am confused on this problem because there is no current mentioned, and all the equations giving involve current. Then I thought that the circle could be split in two and the force of the two halves would then have to equal zero but that seems wrong as well. Please help I just don't understand :(.

 

[MathStudent]

I believe the arrows in the diagram are meant to be the direction of the current.

Since its all just one long wire, the current everywhere is equal.

You can treat these (line / circle) as separate objects.

 

[Davorak]

There is only one wire, so I think there will be only one current. The magnitude of the current will not matter in the end or they would have told it to you.

Try solving the problem by breaking it up into a circular piece and a straight wire piece.

Calculate the magnetic field each causes in the center of the loop.

By adjusting the R the radius of the loop you should be able to get the magnetic field to equal zero.

Does this make the problem clearer?

edit:
MathStudent beat me to the punch.