Determine the magnetic flux:

A coil is wound uniformly with 300 turns over a steel ring of relative permeability 900, with a mean circumference of 40mm and cross-sectional area of 50 mm². If a current of 25A is passed through the coil, determine (a) m.m.f, (b) reluctance of the ring, and (c) flux.

Solution

 (a)       Coil m.m.f = NI AT = 300 × 25 = 7500 AT.

 (b)       Reluctance of the ring = l/ μ₀ μ_r A = (40 × 10^{- 3})/ (4π× 10 ^{- 7} × 900 × 50 × 10^{- 6})

                                                      = 0.707 ×10⁶ AT/Wb.

(c)  Flux = m.m.f/ reluctance  = 7500 / (0.707 × 10⁶)

                                                        = 10.6 m Wb .