All Problems Constant Magnetic Field, Magnetics
Problem 3.245
A thin insulated wire forms a plane spiral of \(N=100\) tight turns carrying a current \(I=8 \mathrm{mA.}\) The radii of inside and outside turns (Fig. 3.67 ) are equal to \(a=50 \mathrm{~mm}\) and \(b=100 \mathrm{~mm}\). Find: (a) the magnetic induction at the centre of the spiral; (b) the magnetic moment of the spiral with a given current.
3.245. (a) \(B=\frac{\mu_{0} I N \ln (b / a)}{2(b-a)}=7 \mu \mathrm{T}\) (b) \(p_{m}=1 / 3 \pi I N\left(a^{2}+a b+b^{2}\right)=15 \mathrm{~mA} \cdot \mathrm{m}^{2}\).