The inner and the outer radii of a toroid are 9cm and 11cm respectively and the number of turns in it is 3140. A magnetic field of 2.5 Tesla is produced in it when a current of 0.5 ampere is passed in it. The permeability of core material is (in Henry/meter)-

$10^{-3}$

$ \mu = \frac{M}{H} = \frac{M}{\frac{NI}{2\pi r}} = \frac{ 2.5 \times 2\times \pi \times 0.1}{3140\times 0.5} = 10^{-3} Henry/meter$