A magnetic circuit has a mean flux path length of 800 mm and a reluctance of 2.5.105 A-t/Wb. A magnetic flux of 5 mWb is produced in this circuit by an energising coil of 800 turns. Determine the: (i) m.m.f. that must be produced by the coil. (ii) magnetic field strength. (iii) voltage induced in the coil circuit if the magnetic field is allowed to collapse to zero in 2 ms. (iv) inductance of the energising coil.

A flux of 0.0016 Wb flows in a silicon sheet steel coil/core. The arrangement appears as shown below with the following dimensions: Ac = 0.0025 m? Core/gap area: Flux path length: le = 0.350 m lg = 0.0015 m N = 500 Air gap length: Number of turns: %3D A. What is the current, I, through the winding? B. What is the energy stored in the inductance? C. Assume that the current is given by i =9.75 sin (3147) A. What is the RMS voltage that would appear across the winding? D. Assume that the gap is removed from the arrangement with the flux path remaining at 0.350 m. For a flux of 0.0016 Wb, what is the inductance of the arrangement? E. What is the energy stored in the inductance with the gap removed?

An air-cored choke is designed to have an inductance of 20H when operating at a flux density of I Wb/m²: the corresponding relative permeability of iron core is 4000. Determine the number of turns in the winding: given that the flux path has a mean length of 22 cm in the iron core and I mm in air gap and that its cross-section is 10 cm².