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UNESCO
TECHNICAL &amp;
VOCATIONAL EDUCATION
REVITALISATION PROJECT-PHASE
PROJECT
II
NATIONAL DIPLOMA IN
ELECTRICAL ENGINEERI
ENGINEERING
NG TECHNOLOGY
Low
Low
High
_
I
10
10 Ohms
Ohms
High
_
+
V
+
R
100 volts
ELECTRICAL ENGINEERING
SCIENCE (I)
COURSE CODE:
CODE EEC 115
YEAR II SEMESTER I
PRACTICAL
Version 1: December 2008
TABLE OF CONTENTS
Department
Electrical Engineering Technology
Subject
ELECTRICAL ENGINEERING SCIENCE (I)
Year
1
Semester
1
Course Code
EEC 115
Credit Hours
3
Theoretical
1
Practical
2
ELECTRICAL ENGINEERING SCIENCE (I)
PRACTICAL
WEEK 1: Basic Electrical quantities measurement
WEEK 2: Measurement of voltage and current
WEEK 3: Measurement of resistance
WEEK 4: Ohm’s law
WEEK 5: Series circuit connections
WEEK 6: Parallel circuit connections
WEEK 7: Resistance in parallel
WEEK 8: Capacitor in circuit
WEEK 9: Voltage division principle
WEEK 10: Series-parallel connected resistors
WEEK 11: Kirchhoff’s current law
WEEK 12: Kirchhoff’s voltage law
WEEK 13: Resistivity
WEEK 14: Power in d.c. circuit
WEEK 15: Charging and discharging of a capacitor
2
This Page is Intentionally Left Blank
3
Basic Electrical Quantities Measurement
Week 1
TITLE:- Basic Electrical Quantities Measurement
It is necessary
knowing how to measure voltage, current, and resistance.
Special types of instruments are used to measure these basic electrical quantities. The
instrument used to measure voltages is a voltmeter, the instrument used to measure
current is a ammeter, and the instrument used to measure resistance is a ohmmeter.
Commonly, all three instruments are combined into a single instrument such as
a multimeter or AVO meter ( Ampere- Volt-Ohmmeter), in which you can choose
what specific quantity to measure by selecting the switch setting.
Figure (1) shows typical portable multimeters, part (a) from figure shows
analog multimeter with pointer, and part (b) shows a digital multimeter with digital
screen.
(a) Analog multimeter
(b) Digital multimeter
Figure (1) Typical portable Multimeter
General scheme symbols is used to indicate placement of meters in circuit
when value changes need to be shown. Figure (2) shows meter symbols used to
present the different meters, as voltmeter, ammeter and ohmmeter.
4
+
V
_
+
A
_
Ω
_
0.00
+ V _
(a) Voltmeter
0.00
+ A _
(b) Ammeter
+
0.00
+ Ω _
(c) Ohmmeter
Figure (2) Meter symbols
How to use Analogue meter:
Figure (3) shows a typical multimeter. This device can measures the three electric
quantities. The following step shows how to obtain readings from a multimeter.
1.Set the range of the desired quantity to be measured to the highest value.
2.Connect the leads to the right terminals at the meter
3.Switch on the circuit if necessary.
4.Adjust the range until you get clear readings.
5.Apply the following formula to obtain the measured quantity.
Re ading &times;
Range
Full − Scale
For example, referring to figure (3),the reading was 3.5 from a full-scale value of 5V,
as shown in the small box.The range was set to X300V.So the measured voltage is
3 .5 &times;
300
= 210
5
5
Figure(3): Multimeter
Note:
The scale has to be viewed from an angle perpendicular to it.
6
Measurement of Voltage and Current
Week 2
TITLE: Measuring the Voltage
Voltage can be considered as the pressure that force the electrons to flow. The
voltage is being measured by measuring the difference between the voltages at the two
terminals of the device-under-test which is the (voltage drop). This can be performed
using a measuring instrument called voltmeter.
The voltmeter connection in the circuit is a parallel connection.
Figure (1) illustrates how to connect voltmeter in the circuit to measure the
voltage across the resistor.
Procedure
1.
Adjust the range of the meter
2.
Connect the leads in the true terminals of the meter
3.
Apply the other ends of the leads to the resistor under test
4.
Record the reading and apply the formula Re ading &times;
Range
full − scale
7
Measuring Current with Ammeter
It is well known that current in the circuit is measured by ammeter, to measure
the current , the circuit must be open and the ammeter is connected in series the
circuit.
Procedure
1.
Connect the simple circuit shown in the figure below
2.
Open the circuit between the source and the resistor
3.
Connect the ammeter terminals to one end of the resistor and to the source
4.
Switch on the power supply and record the reading.
5.
Apply the formula Re ading &times;
Range
if necessary
full − scale
Note:
If the meter did not give any movement or tried to move backward, then switch the
terminal leads with each other
8
Figure(1) illustrates how to connect ammeter in the circuit and measure the current.
Figure 1: Example of an ammeter connection
9
Measurement of Resistance
Week 3
TITLE:- Measuring Resistance with Ohmmeter
To measure resistance, connect the ohmmeter across the resistor. The resistor must
+
+
first remove from the circuit. This procedure is shown in figure (2).
Procedure
1.
Adjust the meter so that when the two terminals are short circuited, the ohmmeter
reads zero
2.
Disconnect the resistor to be measured from the circuit (why?)
3.
Apply the meter leads to the resistor terminals (resistor is parallel to the meter)
4.
Record the reading and apply the formula Re ading &times;
Range
if necessary
full − scale
10
Ohm’s Law
Week 4
TITLE: Ohm's law
OBJECTIVE:- Verification of Ohm’s Law
Ohm‘s law is the most important mathematical relationship between voltage,
current and resistance in electricity.
V=IXR
It is important to know how to read the resistors' colour code and hence its ohmic
value. In the following figure it shows a table of the meaning of each colour. For
example, for the resistor in the figure(1),the value of the resistor is 200kΩ,since the
band 1 is red i.e. equivalent to 2 in the table ,band 2 is black equivalent to zero in the
table and the band 3 is yellow indicating of a multiplier of 10,000.see at the bottom of
the figure.
The fourth band is the tolerance band i.e the percentage of error. It usually
comes in two colors ,the silver indicates &plusmn;5% and the gold indicates &plusmn;10%.so for
example, the value resistor will lie between 210kΩ and 190kΩ.
Procedure
1.
Select a number of different resistors
2.
Use the table below to determine their values
3.
Use ohmmeter to measure the same resistors you figured out
4.
Compare your calculated values with the readings you obtained
11
Resistors color code:
Ω
&plusmn;5%
Figure 1:Resistors colour code
12
Series Circuit Connection
Week 5
TITLE:- series circuit
OBJECTIVE: verification of series circuit
There are three basic types of circuits, series, parallel and series-parallel circuits.
Series circuit:
Series circuit is the simplest circuit. The conductors, loads and power supply are connected
with only one path for the current. The same amount of current will flow through each load.
However, the voltage across each load will be different. Figure(1) shows different
configuration of series circuits.
Procedure:
1.
Connect a number of resistors is series
2.
Measure the current in the circuit. What do you notice?
3.
Connect two identical lamps in series. Notice the brightness of the lamps
4.
Add one more lamp to the circuit you connected in step 3. What do you notice?
5.
Repeat step 4 with more lamps and measure the current in all cases
6.
Write a conclusion
13
Figure1 : Different configuration of series circuits
14
Parallel Circuit Connections
Week 6
TITLE: Parallel circuit:
OBJECTIVE: To verify parallel circuit
The main difference between a series circuit and a parallel circuit is in the way
the components are connected. Parallel circuit should have at least two loads
connected separately to the voltage source, so the voltage across the loads are the
same. However, in a parallel circuit the electric current has several paths that it can
travel. Figure(2) shows different configuration of parallel circuits.
Procedure
1.
Connect a number of resistors is parallel as shown below
2.
Measure the current in each branch and the total current. Comment on
the readings
3.
Add more resistors in parallel. Repeat step 2
4.
Measure the voltage across each resistor. Comment on your results
15
Figure1: Differe
16
Resistance in Parallel
Week 7
TITLE:- Resistance of parallel connected resistors
OBJECTIVE: To verify parallel connection circuits
1. To measure the total resistance of combinations of parallel connected resistors
resistors.
A parallel circuit is a circuit with more than one path for current flow.
Removing one branch of a parallel circuit does not affect the operation of (the
current in) the remaining branch circuit. The total resistance of parallel connected
resistors is less than
han the resistance of smallest branch resistor. There are many
parallel circuits in electronic equipment. The formula for calculating RT for
parallel resistors is:
1/RT = 1/R1 + 1/R2 + 1/R3 +……..+ 1/Rn
RT = R1xR2xR3 / R1R2+R2R3+R3R1
Materials Required:
Multi-meter.
Resistors: all &frac12; watt, 330 Ω, 470 Ω, and two 1200 Ω.
Procedure:
1) Refer to the following figure choose the resistors shown as combination A.
2) Measure the resistance of each of the resistors supplied for combination A.
Record the measured value of each resistor in the column beneath is colour
coded value in the following table.
3) Measure the RT of the parallel combination and record your reading in the
column label “Measured RT “in the following table.
Ohmmeter
Parallel
Combination
Group A
Group B
Group C
Colour
coded
value
Measured
value, Ω
Measured
value, Ω
Measured
value, Ω
R1
R1
R1
R1
330 Ω
470 Ω
1200 Ω
1200 Ω
X
X
Measured
RT
Ω
X
X
X
Questions:
Q1) was the value RT greater or smaller than the value of the smallest branch resistor
in each combination?
Q2) Combination (group C) placed two resistors of equal value in parallel. From the
results of measuring RT of this combination of resistors, suggest a general rule for RT
of any two resistors of equal value connected in parallel.
Q3) what is the RT of three 330 Ω resistors in parallel?
Variable Resistors.
Objective:
To measure resistance between the variable (centre terminal) and the terminals
on other side of it as the shaft of a potentiometer is turned from its minimum to
maximum position.
Materials Required:
1) Multi-meter.
2) Variable Resistor 10000 Ω Potentiometer.
Procedure:
1. Examine the potentiometer assigned to you. Place it so that the shaft points
toward you. Measure and record in the following table the value of
potentiometer between the two outside terminals.
2. Turn the shaft to any position (1) and measure the resistance between the left
terminal (A) and the centre terminal (C) Record this reading in the following
table .
3. Without moving the shaft, measure the resistance between the right terminal
(B) and the centre terminal (C), Record this reading RBC in the table.
4. Complete the table.
A
C
B
19
Table 6.1
Step
Potentiometer
shaft setting
RAB
Ω
1
Any
2
Position 1
X
3
Position 2
X
4
C.W
X
5
C.C.W
X
RAC
Ω
RBC
Ω
RAC + RBC
X
X
X
Questions:
Q1) In the potentiometer above, what is the relation between RAC, RBC, and RAB? Do
your measurements confirm this relation?.
Q2) In what position of the shaft is the resistance between A and B minimum?.
Q3) In what position of the shaft is the resistance between.
20
Capacitor
Week 8
TITLE: Capacitor in a circuit
OBJECTIVE: To test capacitor by observing their charging and discharging using an
ohmmeter.
Capacitor is a device that stores energy in the electric field created between a pair of
conductors on which equal but opposite electric charges have been placed. Capacitance is a
measure of a capacitor's ability to store charge. A large capacitance means that more charge
can be stored. Capacitance is measured in farads, symbol (F). However 1F is very large, so
prefixes are used to show the smaller values.
Three prefixes (multipliers) are used, &micro; (micro), n (nano) and p (pico):
•
&micro; means 10-6 (millionth), so 1000000&micro;F = 1F
•
n means 10-9 (thousand-millionth), so 1000nF = 1&micro;F
•
p means 10-12 (million-millionth), so 1000pF = 1nF
Materials Required:
•
•
Ohmmeter.
Capacitor.
Fig 8.1
Procedure:
1. Connect the circuit as shown above.
2. Read the ohmmeter and record the conditions of the capacitor which are:
a. If the ohmmeter reading move toward zero and then slowly returns to
infinity means the capacitor is in a good condition.
b. If the ohmmeter move towards zero and remain at zero means the
capacitor is short circuited .
c. If the reading doesn’t change and remains at infinity means the capacitor
is open circuited.
3. Replace the capacitor and repeat step 1 and 2.
4. Repeat step 3 until all capacitors are tested.
Table 8.1
Capacitor
Reading
Remark
Ans
wer
C1
the
foll
owi
C2
ng
que
stio
C3
ns:
Q1)
What is the meaning of capacitance?
Q2) Draw the symbol of a capacitor?
Q3) State 1 application for capacitors?
Q4) complete the following:
22
•
If the ohmmeter reading move toward zero and then slowly returns to infinity
means
•
………………………
the ohmmeter move towards zero and remain at zero means
…………………………
•
If the reading doesn’t change and remains at infinity means
…………
23
Voltage Division Principle
Week 9
TITLE: Voltage divider
OBJECTIVE: Verify the operation of voltage divider
APPARATUS:
(1)
2 Digital multimeters
(2)
Variable power supply
(3)
Resistor R1 = 330Ω
Resistor R2 = 1KΩ
Resistor R3 = 500Ω - Trimmer
PROCEDURES:
(1)
Connect a digital multimeter as d.c voltage, and another one as milliammeter
fig 9.1
(2)
Set the switch S1 to OFF
(3)
Adjust the voltage to 5V by turning the variable power supply
(4)
Read the value of the voltage V0 (no load) between point 3 and earth and write
it down in table 9.1
(5)
Calculate the value of the voltage V0 (no load) and write it in table 9.1
(6)
turn the trimmer R3 completely clockwise
(7)
Set the switch S1 to ON
(8)
Read the values of the voltage and of the current and write them in table 9.1
(9)
Repeat the previous operation for all the values of R3 shown in table 9.1
(10)
Represent in fig 9.2 the characteristic curve voltage-current of the voltage
divider
(11)
Comment on the results
24
R1
1
2
3
S1
ON
ON
A
com
R2
VS
R3
V
A
Voltmeter
com
Milliammeter
Fig 9.1
Table 9.1: Obtained Results
V0(no load [V]
Measured
V0(no load) [V] R3 [Ω] 500 400
calculated
V0 [V]
300
200
100
0
I0[mA]
V0(V)
I0(mA)
Fig 9.2
25
Series-Parallel Connection of Resistors
Week
10
TITLE: Series-Parallel Resistors
OBJECTIVES: Observe the behaviour of series-parallel connected resistors
APPARATUS:
(1)
Digital multimeter
(2)
Resistor R1 = 1KΩ &plusmn; 5%
Resistor R2 = 1KΩ &plusmn; 5%
Resistor R3 = 220KΩ &plusmn; 5%
PROCEDURE:
(1)
Set the switches S1 and S2 to ON
(2)
Connect a multimeter, set as ohmmeter, fig 10.1
(3)
Write down in table 10.1 the value read in the ohmmeter
(4)
Calculate the value of the resistance R12 and write down the value in table 10.1
(5)
Compare the measured value with the calculated one
(6)
Move a terminal of the ohmmeter from the jack 2 to the jack 1
(7)
Set the switches S1 to ON, and S2 to OFF
(8)
Write down in table 10.1 the value read in the ohmmeter
(9)
Calculate value of the resistance R13 and write down the value in table 10.1
(10)
Compare the measured value with the calculated one
(11)
Set the switches S1 and S2 to ON
(12)
Write down in table 10.1 the value read in the ohmmeter
(13)
Calculate the value of the resistance Re and write down the value in table 10.1
(14)
Comment on the measured value with calculated one
26
1
R3
2
R2
R1
ON
com
V
S1
S2
Fig 10.1
Table 10.1: Obtained Results
R12 [Ω]
R12 [Ω]
R13 [Ω]
R13 [Ω]
Re [Ω]
Re [Ω]
Measured
calculated
Measured
Calculated
Measured
Calculated
27
Kirchhoff’s Laws
Week
11
TITLE:- Kirchhoff’s Current |Law
OBJECTIVE: To verify Kirchhoff’s law
APPARATUS:
(1)
Variable power supply
(2)
Voltmeter
(3)
Milliameter
(4)
Resistor R1 = 1KΩ &plusmn; 5%
Resistor R2 = 1KΩ &plusmn; 5%
Resistor R3 = 220KΩ &plusmn; 5%
PROCEDURES:(1)
Connect multimeter, set as a d.c voltmeter, and another one as milliameter, Fig
11.1
(2)
Adjust the voltage to 10V by turning the variable power supply
(3)
Set the switches S1 to On, S2 and S3 to OFF.
(4)
Write down in table 11.1 the values read on the voltmeter and on the
milliammeter.
(5)
Set the switches S2 to ON, and S1 and S2 to OFF
(6)
Write down in table 11.1 the values read on the voltmeter and on the
Milliammeter
(7)
Set the switches S3 to ON, S1 and S2 to OFF
(8)
Write down in table 11.1 the values read on the voltmeter and on the
milliammeter
(9)
Calculate the value of the current in the single resistors and write down the
results in table 11.1
(10)
Compare the calculated values with the measured ones.
(11)
Verify that the sum of the current that go in the node 2 is equal to the sum of
the current that go out.
(12)
Comment on the result in steps (10) and (11)
28
2
2
1
S1
2
S2
S3
ON
ON
Fig 11.1
com
R3
R2
R1
A
V
Fig 11.1
Voltmeter
com
Millammeter
Table 11.1: Obtained Results
VR1
I1
VR2
I2
VR3
I3
I1
I2
I3
[V]
[mA]
[V]
[mA]
[V]
[mA]
[mA]
[mA]
[mA]
Measured Value
∑I=0
Calculated value
29
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