Physics

Problem

A coil having

N

turns is wound tightly in the form of a spiral with inner and outer radii

a

and

b

respectively. When a current

I

passes through the coil, the magnetic field at the center is a.

\frac{\mu_0 NI}{b}

\frac{2\mu_0 NI}{a}

\frac{2\mu_0 NI}{2(b-a)} \ln \frac{b}{a}

\frac{2\mu_0 NI}{2(b-a)} \ln \frac{a}{b}