Elc practical

1. 1
Introduction
Electricity is an essential part of the modern life experience, and as an engineer it is essential to know
how it behaves and responds to changes in its trajectory. This lab was divided into two parts namely
Part 1 is about measuring resistance using the colour coding technics and proving it with the (Digital
Multimeter) hence forth referred to as (DMM) and part 2 is working with the power supply and
the(DMM) to determine voltage. The main goal of the lab is to get used to carbon resistors and
determining their values from specification (colour codes) and measurements. And to show that the
colour code method of identifying resistance tolerance through its colour coding is relatively
accurate. The purpose is to get familiarized with lab equipment, analyse simple resistors, measure
circuit properties such as voltage and resistance through two conductors.
Theory
Basic definitions needed for the complete understanding of the content of this report:
 Voltage is electrical potential energy per unit charge which is measured in joules per
coulomb which has its SI unit as volts.
 Resistance is defined as the opposition within a conductor to the passage of electric current
which has its SI unit as Ohms (Ω). Carbon resistor are the components which are placed in a
circuit to oppose current flow.
 Power supply is a device that supplies electric power to an electrical load.
Basic formulas & other relevant information
퐶푙푎푐푢푙푎푡푒푑 푣푎푙푢푒−푀푒푎푠푢푟푒푑 푣푎푙푢푒
퐶푎푙푐푢푙푎푡푒푑 푣푎푙푢푒
× 100 (푬풒풖풂풕풊풐풏 ퟏ)
Tolerance Colour Codes
No Band = 20%; Silver = 10 %; Gold = 5% and Red=2%.

2. 2
Pre-Lab
Question 1:
a) R= (Brown, Black)×10red
R= 10×102= 1000Ω
Tolerance= Silver= 10%
10
100
× 1000 = 100Ω
Therefore this resistor has a value tolerance between 900Ω and1100Ω
b) R= (Red, Green, Black) ×10brown
R= 250×101= 2500Ω
Tolerance= Red = 2%
12
100
× 2500 = 50Ω
Therefore this resistor has a value tolerance between 2450Ω and 2550Ω
b) R= (Brown, Black)*10blue
R= 10×106=10MΩ
Tolerance= Gold= 5%
5
100
× 10000000 = 500000 Ω =0.5 MΩ
Therefore this resistor has a value between 9.5MΩ and 10.5MΩ
Question 2:
a) 1.75 kΩ ±2%
1.75×1000= 1750 Ω
According to the Colour codes 1=brown, 7= violet, 5=green, brown= 2 and red is 2%
The colour code is {Brown, Violet, Green, Brown, and Red}
b) 10MΩ ±5%
10×106= 10000000 Ω
According to the colour codes 1= brown, 0= black, 6= blue and gold is 5%
The colour code is {Brown, Black, Blue, and Gold}

3. 3
c) 38kΩ ±5%
38×1000= 38000
According to the Colour codes 3= orange, 8= grey, 3= orange and gold is 5%
The Colour code is {Orange, Grey, Orange, and Gold}
Equipment used
 Power supply
 Digital Multimeter (DMM) which serves as a Voltmeter and Ammeter
 Three carbon resistors with different resistances
 Two conductors
Procedures
To Measure Voltage:
Change the voltage selection knob on the DMM to (DC or –V) for DC measurement. Voltage is
measured in parallel with the load and the range of your measurement can be altered by using the
Range buttons.
To Measure Current:
Change the current outlet of the DMM to (“+” terminal) and the COM outlet (ground). Current is
measured in series you will have to break the circuit to measure current. For a current less than
200mA use the outlet (VΩA) and for current greater than 200mA use the outlet written 20A
in red else the DMM will not be accurate and may not show the current reading. You can vary the
range of your measurement by using the Range buttons.
To Measure Power Supply Voltage:
A voltmeter is always connected in parallel across your load or power supply. The “+” terminal of
the voltmeter should be connected to the “+” terminal of the Power Supply hence forth referred to
as (PS) (usually the red outlet) and the “-” terminal of the voltmeter to the “-” terminal of the PS
(usually the COM or black outlet) of the DMM.
Part 1 of the lab
1. Push the power button to turn on the multi-meter.
2. To use the DMM as an ohmmeter, turn the knob so that it points on the side of resistance,
where there is (Ω) symbol.
3. Get three resistors from your toolbox.

4. 4
4. From the colour code of each resistor, determine the resistance and the tolerance of each
resistor.
5. Calculate the range of resistance values for each resistor based on the tolerance of the
resistors.
6. These results were recorded on the table provided.
7. Using the DMM, measure the resistance of each resistor.
8. To do this try to seek advice from the laboratory assistant (insert a red banana-to-clip
connector into the Ω-plug and a black banana clip connector into the COM-plug). Place the
resistor-under-test between the red and the black connectors.
9. Record this on the table provided.
Part 2 of the lab
1. Set the Meter knob of the PS to the +5 V position, and connect the two wires from the PS (+
V and COM outlets) to the voltmeter.
2. Since you’re measuring DC voltage, press the --V button and maximum range on your
Multimeter.
3. Adjust the output of the PS by using the Voltage +5 V knob.
4. Check your voltage by reading the volts scale of your PS (lower reading) and compare it to
the voltmeter reading.
Results
Part 1 results: Measuring Resistance
Exercise
Calculations using Equation (1) % Error
R1=
560−570
560
× 100 = -1.79%
R2=
27−27.2
27
× 100 = -0.74%
R3=
47−46.9
47
× 100 = 0.2%
Table 1
Resistor Colour Codes Value of resistance
calculated from colour code
Measured value
or resistance
% Error
R1 Green, Blue, Brown, Gold 560Ω ±5% 570Ω -1.79%
R2 Red, Violet, Black, Gold 27Ω ±5% 27.2Ω -0.74%
R3 Yellow, Violet, Black,
Gold
47Ω ±5% 46.9Ω 0.2%

5. 5
Table 2
Part 2: Use of Power Supply
Exercise
 Readings from Power Supply and Voltmeter respectively…
Power Supply Voltmeter
5V 5.05V
10V 9.96V
15V 15.03V
20V 19.9V
25V 24.9V
30V 29.8V
Table 3
Discussions
Part 1:
Tolerance for all the resistors is more or less 5%. The negative percentages just mean that the amount
that we have calculated has been exceeded by that percentage, and the positive percentages just mean
that the amount that we have calculated has not been exceeded by that percentage. All the errors for
each resistance measured fall within the calculated ranges. Therefore the method of calculating
resistance ranges using colour codes is approximately accurate and can be used as an alternative to
measuring the resistances all the time.
Part 2:
The reason why the voltmeter readings are slightly lower or bigger is because the power supply has
an internal resistance. Within the conductors energy is converted into other forms of energy such as
(heat) causing the voltage drop. This affects the potential difference as proven above with table
number 3.
Conclusion:
In conclusion I have learned how to operate the DMM and that making the use of colour codes to
calculate the resistance of a resistor is faster than actually measuring that resistance. The errors due
to these calculations is very small and is within the range of resistivity of the resistor. There is also
the matter of the conversion of electricity from one form to another that I have noticed while doing
the last exercise in which the voltage readings are quite different from the real ones. This is due to

6. 6
the elements that contribute to the resistance namely (length of conductor, material of conductor,
cross sectional area of the conductor and the material from which the conductor is made from).
Furthermore I think that these findings were useful in the sense that I now understand more about
electrical circuits than before these lab and that it will contribute to the foundation of my engineering
career.