A coil of 300 turns is wound uniformly on a ring of non-magnetic material. The ring has a mean circumference of 40 cm and a uniform cross-sectional area of 4 cm2. If the current in the coil is 5A, calculate the magnetic field strength, (b) the flux density and (c) the total magnetic flux in the ring.
The ring is very elongated and not circular because the circumference and csa are inconsistent with a circle: radius r circum / 2pi 6.366 cm radius r sqrt (csa / pi) 1.128 cm The general formula for magnetic field strength is B u0*N*I / distance (units of Tesla or Weber per sq m) u0 4pi*10^-7 H/m N 300 turns I 5A distance ? distance 2r for a flat circular coil (b) flux density in Wb/m^2 is the same as field strength in Tesla (c) total flux flux density * csa (would actually be less than this, because B is max at the centre and not constant) Hope this helps
