MBS3129 Electrical Principles
Tutorial 1
1. A laminated section of core has cross-sectional dimensions of 0.03 m by 0.05 m.
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(a) What is the effective area of the core? [1 .5x10 m ]
(b) Given Φ = 1.4 x 10-3 Wb, what is the flux density, B? [0.933T]
2. For the section of iron core of the below figure, if Φ1 = 12 mWb and Φ3 = 2 mWb, what is B2? [1T]
3. Consider the below figure, If I = 10A, N = 40 turns, r1 = 5 cm and r2 = 7 cm, what is H in ampere-
turns per meter? [1061 At/m]
4. A mild-steel ring having a cross-sectional area of 500 mm2 and a mean circumference of 400 mm.
If a coil of 200 turns wound uniformly around it and the relative permeability is 380. Calculate:
(a) the reluctance of the ring; [1.68 x 106 A/Wb]
(b) the current required to produce a flux of 800 μWb in the ring. [6.7A]
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5. Find the current I in the below figure if Φ = 0.16 mWb.
Given Hsteel = 350 At/m, Hiron = 1550 At/m [0.47A]
6. A magnetic circuit in the form of a metallic core is shown in below. Give that current i = 120mA;
coil turn N = 500 turns; mean path length l = 60 cm and the cross-sectional area A = 2 cm2.
(a) Determine the magnetomotive force (Fm) produced by the coil;
(b) Calculate the average magnetic field strength (H) in the core;
(c) If the relative magnetic permeability (r) of the core material is 1200, find the average
magnetic flux density (B) in the core.( mO = 4p x 10-7 H/m);
(d) Determine the total flux () in the core. [60A, 100a/m, 0.15T, 30 Wb]
7. A cast steel magnetic circuit with N = 2500 turns, I = 200 mA, and a cross-sectional area of 0.02m 2
has an air gap of 0.00254m. Assuming 90% of the mmf appears across the gap, estimate the flux in
the core. (Given: The permeability of free space, μo= 4π x 10-7 ; μr =1 )
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[4 . 4 x10 Wb ]
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8. Flux changing at a uniform rate for 1ms induces 60V in a coil. What is the induced voltage if the
same flux change takes place in 0.01s? [6V]
9. The current in a 75mH inductor changes uniformly by 200A in 0.1ms. Find the induced voltage?
[150mV]
10. Find LT for the circuits at right. [21H, 2H, 20H, 4H]
11. Find the energy stored in the inductor of the below figure. [0.32J]
End
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