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. Please view the attachment below for the complete question and the diagram.

Electromagnetic Forces and Field

Electromagnetic Forces and Field. See attached file for full problem description.

Flux density in an iron core.

A magnetic circuit consists of an iron core of a cross sectional area of 4cm^2 in which a cut in an air gap where a flux density of 0.9T is required. There is a leakage factor of 1.2 and fringing increases the cross sectional area of the gap by 10%. What should be the flux density in the iron?

Working with the boundary between two dielectrics. Attachments in Word.

In Figure A1 below the boundary between two ideal dielectrics is shown. Near the boundary, on Er1 side, the electric field is measured and found to be perpendicular to the boundary and equal to 100 Vm-1. a) What is the direction of the electric field E, near that boundary? b) What is the magnitude of E2? Please see attachment below for the complete question.

Self inductance of coil

A coil of 500 turns is wound on a wooden ring having a mean diameter of 8cm and a cross sectional area of 1.5cm^2. Assuming relative permeability of wood is 1, calculate the self-inductance of the coil and the emf induced in it when the direction of a dc current of 5A flowing in it is reversed in 0.2sec?