Magnetic Field of a Toroid

1. The problem statement, all variables and given/known data
"The toroid shown in the figure has a wire carrying a current I= 7.80 Amperes wrapped around it N= 920 times. The inner radius is R1 14.0 cm and outer radius R2 16.8cm. What is the magnitude of the magnetic field along a circle that is halfway between the inner and outer edges of the toroid?"

2. Relevant equations
Magnetic field of a Toroid: B=μ0NI/2πr
B=magnetic field
μ0=permeability constant=4πx10-7 N/A2
N=number of times the wire is wrapped around the toroid

3. The attempt at a solution
Since the problem is asking for the field in the middle of the toroid, I decided to set my radius to halfway between the outside and inside:
16.8 cm-14 cm=2.8 cm
r=14+2.8 cm=.168 m

When I plug in this and all the variables given to me, my answer comes up wrong. Is there a concept I’m missing? My class never covered toroids so I’m pretty much on my own for this one.


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