The magnetic coils of a tokamak fusion reactor are in the shape of a toroid having an inner radius of 0.700 m and an outer radius of 1.20 m. The toroid has 900 turns of large diameter wire, each of which carries a current of 13.0 kA. Find the difference in magnitudes of the magnetic fields of the toroid along the inner and outer radii. (Enter your answer in T.)

The difference is

Explanation:

From the question we are told that  

    The inner radius  is  

        The outer radius  is  

        The number of turns is  

        The current on each wire is

Generally magnetic field of a toroid along the outer radius is mathematically evaluated as

Where   is the permeability of free space with value

substituting values

Generally magnetic field of a toroid along the inner radius is mathematically evaluated as

substituting values

The difference in  magnitudes of the magnetic fields of the toroid along the inner and outer radii is mathematically evaluated as

i think the answer is a, hope this : )