How to Calculate the Magnetic Field in a Toroid?

[swashbuckler77]

Homework Statement

"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?"

Homework Equations

Magnetic field of a Toroid: B=μ₀NI/2πr
B=magnetic field
μ₀=permeability constant=4πx10^-7 N/A²
N=number of times the wire is wrapped around the toroid
I=current
r=radius

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!

 

[swashbuckler77]

So according to the rules I can bump the thread once after 24 hours has passed since the initial post was created? Sorry, I just really need help on this. Is it because the question is so easy to everyone else that it should be obvious what I'm doing wrong? I feel so dumb not knowing how to do this...

 

[rude man]

Homework Statement

"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?"

Homework Equations

Magnetic field of a Toroid: B=μ₀NI/2πr
B=magnetic field
μ₀=permeability constant=4πx10^-7 N/A²
N=number of times the wire is wrapped around the toroid
I=current
r=radius

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

Hey man, instead of in the middle you just wound up back at the outer radius for your value of r!

Compute r again.