**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=μ_{0}NI/2πr

B=magnetic field

μ_{0}=permeability constant=4πx10^{-7} N/A^{2}

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!

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