defence exam Agniveer Vayu Group X & XY Mock Test 01/2026 Physics Moving Charges and Magnetism Magnetic Field on the Axis of a Circular Current Loop
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 centre is
1
\(\dfrac{\mu _{0}Ni}{b}\)
2
\(\dfrac{2\mu _{0}Ni}{a}\)
3
\(\dfrac{\mu _{0}Ni}{2(b-a)}\ln\left ( \dfrac{b}{a} \right )\)
4
\(\dfrac{2\mu _{0}Ni}{(b-a)}\ln\left ( \dfrac{b}{a} \right )\)