Magnetism

Problem 165: A magnetic ring (relative permittivity = 800) has a mean radius of 10 cm and a cross sectional area of \(5\,cm^2\). An air gap measuring 1.5 mm is cut in the ring. Determine the required mmf in order to produce a flux of 0.25 mWb in the air gap.

Problem 166: A magnetic ring with a mean diameter of 25 cm and a cross sectional area of \(5\,cm^2\) is wound with a coil of 600 turns. An air gap of 4 mm is made by cutting a section of the ring. A current of 10 A is passed through the coil. Determine the energy stored in the air gap. Assume relative permittivity of the ring to be 1000.

Problem 167: A permanent magnet loudspeaker is equipped with a 10 ohm 10 turn voice coil wound on a tube 1 inch in diameter. The flux density in the air gap is 10,000 lines per square inch. If the impedance of the voice coil is a pure resistance, what will be the maximum thrust delivered to the core if the impressed signal is 20 dB above 0.005 watt?

Problem 168: A small single-phase transformer has 10.2 watts at no load. The core has a volume of 750 cubic cm. The maximum flux density is 10,000 gauss and the hysterisis constant of the core is \(5\times10^{-4}\). Using the Steinmetz law to find the hysterisis, determine the eddy current loss.