Magnetic circuits – Tutorial
1. A rectangular magnetic core of limb width 4cm has a dimension of 20x3x18 cm3 (l x b x h) and has a
relative permeability of µr = 1500. Find the reluctance of the magnetic core. If a coil of 200 turns is
wound on one limb of the core and a current of 2 A is passed through it, then find the inductance,
magnetic flux, flux intensity and flux density established in the magnetic core.
2. A rectangular iron magnetic core of limb width 4cm has a dimension of 20x3x18 cm3 (l x b x h) and
has a relative permeability of µr = 1500. If a small portion of length 1 cm is cut from the magnetic core,
then determine the effective reluctance of the magnetic core, and current required to establish a flux
of 1.5 mWb. Also, determine the total MMF established in the core and flux density. Assume, due to
fringing, the air gap area is 1.2 times the core area.
3. A rectangular magnetic core has core area = 25 cm2, core length = 50 cm, gap length = 4 mm and N
= 600 turns. For producing a flux density of 1.2T, find total reluctance of the circuit, flux, MMF, and
the current in the coil. Assume relative permeability as 10,000 and neglect fringing effect.
4. A circular magnetic ring having a mean core length of 50 cm, cross sectional diameter of 2.85 cm
has a gap of 2mm along its periphery. If the ring has a coil of 500 turns and the airgap flux is 0.8mWb,
then find the excitation current in the coil by (a) neglecting fringing effect, (b) Include fringing effect,
use Ag = 𝜋(𝑑𝑐/2 + 𝑙𝑔)2 . Assume µr = 500.
5. For the magnetic circuit shown in the below figure, find the effective reluctances of each side, mmf
and excitation current, if the coil which is having 1000 turns sets up a flux of 1mWb in the central limb.
Also, draw the electrical equivalent of the circuit. Take µr = 6000 and neglect fringing effect
6. Two coils with 500 and 1500 turns windings are magnetically coupled to each other. If in the first
winding with 500 turns carry 5A current, a self flux of 0.2m Wb and a mutual flux of 0.4mWb are
produced. Calculate self inductances of the windings, mutual inductance and coefficient of coupling.
7. Find the Thevinin’s and Norton’s equivalent circuit across ab terminals in the above Fig.
8. A 2 winding transformer circuit has following parameters:
Primary winding: R1 = 1.2Ω, X1 = 20Ω
Secondary winding: R2 = 0.3Ω, X2 = 5Ω
The coefficient of coupling k = 0.96. If a load of 𝑍𝐿 = 50∠36.870 Ω is connected to the secondary
winding, the secondary terminal voltage is found to be 100∠00 𝑉, Find the generated coil emfs.