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Electrical Technology (ERT105/EET 103)
Tutorial 4
TUTORIAL 4 – MAGNETIC CIRCUIT
Chapter 4 – Magnetic Circuit
Question 1
State the methods to increase the strength of the magnetic field around the coil.
Question 2
With the aid of diagrams, discuss how a magnetic field can induce a voltage in a
conductor.
Question 3
Briefly explains and draw the diagram on the Right Hand Rule.
Question 4
Briefly explains the method to avoid the stray magnetic field affected the
sensitive measuring instrument.
Question 5
For the series of magnetic circuit in Fig, determine the current I necessary to
establish the indicated flux.
(Answer: I = 1.84A)
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Electrical Technology (ERT105/EET 103)
Tutorial 4
Question 6
Find the magnetic flux, ϕ establish in the series of the magnetic circuit in Fig.
(Answer: ϕ = 6.12mWb)
Question 7
Refer to the figure and B-H curve in figure 4(b), calculate the current I if the flux,
Ф exists in the core is 5 x 10-5 Wb.
(Answer : I=26.78 A)
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Electrical Technology (ERT105/EET 103)
Tutorial 4
Question 8
Refer to the figure 4(a) and B-H curve in 4(b), a flux of 5 x 10-5 Wb exist in the
core. Determine;
i)
The magnetizing force, H in the iron core
ii)
The magnetizing force, H in the air gap if permeability of air is 4π x
10-7 Wb/Am.
iii)
The current, I
Figure 4(a)
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Electrical Technology (ERT105/EET 103)
Tutorial 4
Question 9
A ferromagnetic core is shown in Figure 1 below. The depth of the core is 5 cm.
The other dimensions of the core are as shown in the figure. Find the value of the
current that will produce a flux of 0.005 Wb. With this current, what is the flux
density at the top of the core? What is the flux density at the right side of the core?
Assume that the relative permeability of the core is 1000.
Figure 1
I  2.016 A,
B1  0.67T
B 2  2T
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Electrical Technology (ERT105/EET 103)
Tutorial 4
Question 9
A two-legged core is shown in Figure 2 below. The winding on the left leg of the
core (N1) has 400 turns and the winding on the right (N2) has 300 turns. The coils
are wound in the directions shown in the figure. If the dimensions are as shown,
then what flux would be produced by currents i1 = 0.5A and i2 = 0.75A? Assume
r = 1000 and constant.
Figure 2
  0.00462Wb
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Electrical Technology (ERT105/EET 103)
Tutorial 4
Question 10
If an air gap of 1 mm is cut across the core as shown in Figure 1, calculate the
current I to develop a magnetic flux Φ = 1.08 x 10-3 Wb.
[Ans. I = 1.19 A]
-3
2
A = 2 x 10 m
Cast-steel core
N = 400 turns
1 mm
Mean length
l = 0.16 m
Figure 1
Question 11
Based on ferromagnetic core with 2 leg in figure below, determine :
i)
ii)
iii)
iv)
Magnetizing force on each leg
Magnetomotive force on each leg.
Current, I to establish a given flux.
Total reluctance of the core.
Answer :
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