Question

1.   A flux density of 1.5T is produced in a piece of cast steel by a magnetizing force of 1250A/m. Find the relative permeability of the steel under these conditions.

2.   Determine the magnetic field strength required to produce a flux density of 0.3T in an air gap of length 15 mm. 

Answer 1

1.

$B = \mu_0 \mu_γH \\ \mu_γ = \frac{B}{\mu_0 H} \\ = \frac{1.5}{4 \pi \times 10^{-7} \times 1250} \\ = 955.4$

2. B = 0.30 T

$B = \mu_0H \\ \mu_0 = 4 \pi \times 10^{-7} \\ H = \frac{0.3}{4 \pi \times 10^{-7}} \\ H = 199044 \; A/m$

Magnetomotive force $(MMF) = H \times L$

L = 15 mm $= 15 \times 10^{-3} \;m$

$MMF = 199044 \times 15 \times 10^{-3} = 2985.6 \; AT$