Calculating the current in a resultant magnetic field strength between two coils.

Two single turn circular coils share a common horizontal axis and are separated by a horizontal distance of 2.5m. The radius of one of the coils is 50cm and it carries a current of 5 A. The radius of the other coil is 25cm and it carries a current I in such a direction that the magnetic field which it produces in the opposition to that produced by the current in the first coil. Determine the value of I in order that the resultant magnetic field strength at the mid-point on the axis between the coils shall be zero.

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