Magnetic Field in a Cylindrical Conductor

[Hypnos_16]

Homework Statement

A cylindrical conductor of radius R = 2.49 cm carries a current of I = 2.17 A along its length; this current is uniformly distributed throughout the cross-section of the conductor. Calculate the magnetic field midway along the radius of the wire (that is, at r = R/2).

Radius (m) = 2.49 cm = 0.0249 m = 0.01245 m (as asked)
Current (I) = 2.17 A

Homework Equations

I thought it was B = µI / 2πr because i was given a sheet of equations and this was the only one that seemed to fit it.

The Attempt at a Solution

B = µI / 2πr
B = (4π x 10^-7)(2.17) / 2π(0.01245)
B = 3.49e-5 T

Though this isn't the right answer. Not sure what's gone wrong here.
I also thought it was zero since it's a "conductor" also not right...

 

[Hypnos_16]

Not to worry, i got the answer. I was using the wrong equation.
For values of Magnetic Field inside the given radius the equation is

B = µIr / 2πa^2
B = (4π x 10^-7)(2.17)(0.01245) / 2π(0.0249^2)
B = 8.71e-6 T

In case anyone else had the same or similar problems.