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

I=current

r=radius





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.



Thanks!