Electrical Department of Technology
PTQI
2nd Term Exam (Electricity II)
Student Name:………………..
Student ID:……………………
Question 1: True/False
a) The total resistance of a parallel circuit is always less than the smallest branch resistance.
b) Retentivity is defined as the ability to concentrate magnetic lines of force as compared.
c) The time required for one alteration to be completed is also known as a period.
Question 2: Complete the following
a) All matter is made of ……………………….
b) The symbol of electrical charge is ……………………
c) Parallel circuits can be described as circuit that have …………….path for current to
flow.
d) 5KWh are equivalent to ……………………..MJ.
e) The open circuit voltage of a ni-cad cell is ……………………V
f) The symbol used to represent the henery is ……………………
g) The ……………………..loss is caused by ac voltage stresses with in the insulation of the
conductor.
h) Using silicon steel for the core material of ac equipment reduces the
……………………..losses.
Question 3:
a) Name the three factors that affect the total opposition to current flowing in an ac circuit.
b) What are the four states of atom?
c) State the kirchoff’s voltage Law?
1
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Question 4: Multiple Choice
a) The particles of an atom that rotate in orbital paths are called …………………………..
1) Ions
2) Electrons
3) Protons
4) Neutrons
b) The rate of doing work is expressed in ……………
1) Watts
2) Joules
c) A charged battery contains ………………….
1) Energy
2) Power
d) What type of power production has the widest commercial application?
1) Chemical
2) Solar
3) electro magnetic
4) electrostatic
e) A lithium battery loses about …………………………….% of its charge per month.
1) 25
2) 14
3) 10
4) 5
Question 5:
Calculate the load voltages in series-parallel circuit in Figure 1.
R1
R2
R3
200mΩ
400mΩ
600mΩ
Load 1
15A
E = 240V
Load 2
4A
R6
R5
R4
200mΩ
400mΩ
400mΩ
Load 3
3A
Figure 1
Question 6:
Calculate the voltage drop across a heater that draws 8A is supplied by a cable with a total
resistance of 4Ω. The Supply voltage is 240V?
2
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Question 7:
A 50 µF Capacitor is connected with a 30 KΩ resistor. Determine the time it takes for the
capacitor to become fully charged?
Question 8:
The resistance of a coil is 30Ω and its Inductance is 0.22H. Calculate the inductive reactance of
the coil if the supply is 240V, 50Hz?
Question 9:
a) Calculate the load voltage in the Edison 3-wire system shown in Figure 2
b) If the neutral is accidentally opened, calculate the new load voltages.
R1
100mΩ
_
_
E1= 240V
Load1
+
+
20A
R2
100mΩ
_
_
10A
E = 240V
2
Load2
+
+
R3
100mΩ
Figure 2
3
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Question 10
Equipment wire used as luminair wiring shall not be smaller than # (copper conductor).
abcd-
16 AWG
14 AWG
18 AWG
20 AWG
Question 11
Flexible cord is not to be used for:
abcdef-
cranes and hoists
substitutes for fixed wiring
pendants
circuit run through doorways
all of the above
both B and D
Question 12
A grounding conductor is defined as; the conductor used to connect the electrical equipment to neutral.
a- True
b- False
Question 13
What is the term used to describe a set of conductors run by a supply authority from its mains to a consumer's
service?
abcd-
consumer's service
supply service
service box
service room
4
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Question 14
The term GROUNDING ELECTRODE refers to the conductor which runs from the street side of the water
meter to the panel
a- True
b- False
Question 15
Any device capable of automatically opening an electric circuit, under both predetermined overload and
short-circuit conditions, either by fusing of metal or by electro-mechanical means is called;
abcd-
An overload device
A ground fault device interrupter
An overcurrent device
A zero sequence current transformer
5
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Model Answers:
Question 1
a. True
b. False
c. False
Question 2
a.
b.
c.
d.
e.
f.
g.
h.
Atoms
Q
More than one
18 MJ
1.2V
H
Dielectric
Hysteresis
Question 3
a.
1. Resistance
2. Inductive reactance
3. Capacitive reactance
b.
1. solid
2. Liquid
3. Gas
4. Plasma
c. the algebraic sum of all voltages in a closed circuit is zero. This means that:
•
•
The sum of the voltages rises plus the sum of the voltage drops must equal zero and
The applied voltage equal the sum of the voltages drops.
Question 4
a)
b)
c)
d)
e)
Electrons
Watts
Energy
Electro magnetic
5
6
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Question 5
R1
22A
R2
7A
7A
400mΩ
200mΩ
600mΩ
15A
4A
Load 1
15A
E = 240V
Load 2
4A
15A
R5
22A
400mΩ
7A
V1 = 4.4V
R1
V2 = 2.8V
R2
200mΩ
400mΩ
R4
7A
Load 1
E = 240V
3A 400mΩ
V3 = 1.8V
R3
600mΩ
Load 2
R6
R5
R4
200mΩ
400mΩ
400mΩ
V2 = 2.8V
V4 = 1.2V
V1 = 4.4V
Load 3
3A
4A
R6
200mΩ
R3
3A
Load 3
Vload1 = 240 – 4.4 – 4.4 = 231.2V
Vload2 = 240 – 4.4 – 4.4 – 2.8 - 2.8 = 225.6V
Vload3 = 240 – 4.4 – 4.4 – 2.8 - 2.8 – 1.8 – 1.2 = 222.6V
7
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Question 6
208V
Question 7
One time constant = RC = 30 KΩ x 50 µF = 1.5s
The fully charged time = 5 x 1.5 = 7.5 s.
Question 8
XL = 2πfL = 2π x 50 x 240 = 69.11Ω
Question 9
a. VLoad1 = 237V
VLoad2 = 238V
b. VLoad1 = 185.66V
VLoad2 = 318.44V
Question 10
C
Question 11
C
Question 12
FALSE
Question 13
B
Question 14
FALSE
Question 15
C
8
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