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Oerg
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According to my textbook, the magnetic field of a toroid, according to ampere's law is given above as
[tex] \frac{\mu_0{NI}}{2\pi{r}} [/tex]
but when i was looking through, I found that the magnetic field given by a piece of conducting wire is given as
[tex] \frac{\mu_0{I}}{2\pi{a}}(\cos{\theta_1}-\cos{\theta_2})[/tex]
so that means amperes law must be given for an infinite length of current passing through an area bounded by the loop? If this is the case why does the formula work for the toroid? Is the formula just an approximation in this case where the height of the toroid is really large and the formula for the field is taken to be largely at the center?
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