Resistors, the color code and Ohm’s law
Author Name: Vasilis Leandrou
OBJECTIVES
This report aims to:
 Make the student familiar with the digital and analog ohmmeter.
 To get knowledge of read and use the resistor color code.
 Make the student knowing about how important internal resistance of a voltmeter and ammeter is.
 Become familiar with the dc power supply and setting the output voltage.
 Measure the current in a dc circuit.
 Apply and plot Ohm’s law.
 Determine the slope of an IV curve
BACKGROUND THEORY
In the experiments will be used the VOM, DMM, the color code and power supply to measure the resistance of the provided resistors.
· The VOM employs an analog scale to read resistance, voltage and current.
· The DMM read resistance, voltage and current with a digital display.
· The color code is described in a listing of the numerical value associated with each color.
· Power supplies gives a source of power, rated as maximum voltage and current output
Color code
black 
brown 
red 
orange 
yellow 
green 
blue 
purple 
gray 
white 
0 
1 
2 
3 
4 
5 
6 
7 
8 
9 
Tolerance
brown 
red 
golden 
silver 
None 
1% 
2% 
5% 
10% 
20% 
EQUIPMENT and COMPONENTS USED
· Digital Multimeter (Brand: Good Will Instruments Co. Ltd, Model: GDM8135, Serial Number: CF922334)
· Analog Multimeter (Brand: HAMEG, Model: HM 2036, Serial Number: 46/87 Z33418)
· Power supply
· One 10KΩ resistors
· One 1KΩ resistors
EXPERIMENTAL METHOD AND PROCEDURE
Part 1
The resistance value of 1KΩ and 10 KΩ resistors identified using the color code (table 1.1). The minimum and the maximum resistance are finding by using the following equation (table 1.2).
Maximum value= resistor nominal value + tolerance X resistor nominal value
Minimum value= resistor nominal value – tolerance X resistor nominal value
Part 2
DMM and resistor are connected with wires. The measure from the two resistors is taken. The difference between the normal resistor value and the measured value is finding. The same thing is doing with the VOM (table2.1)
Part 3
The DMM’s internal measured resistance of each dc voltage scale is measured (table3.1). The DMM’s internal measured resistance of each current scale is measured (table3.2).
Part 4
The power supply, changing the values of the voltage we set it on the DMM and the resistors, which had taken new values and found the difference between them (table4.1). The current is measured by the DMM and the difference between the values of the DMM and the current is finding using the Ohm’s law (table4.2). The graphs of the currents are sketching out (graph 1).
I = V
R
OBSERVATIONS, DATA, FINDINGS and RESULTS
Table 1.1 Color code measuring
Resistor (Nominal Value) 
Color BandsColor 
Color bandsNumerical value 

1 2 3 4 
1 2 3 4 
1ΚΩ 
Brown black red gold 
1 0 00 5% 
10ΚΩ 
Brown black orange gold 
1 0 00 5% 
Table 1.2 Minimum and maximum resistance of a resistor
Resistor 
minimum resistance 
maximum resistance 
1KΩ 
950Ω 
1050Ω 
10ΚΩ 
9500Ω 
10500Ω 
Table 2.1 Measure values and difference of a resistor
DMM 
VOM 
Normal Resistor value 
Measure Value 
Falls within Specified Tolerance 
% Difference 
Measure Value 
Falls within Specified Tolerance 
% Difference 
1KΩ 
0.980Ω 
YES 
2% 
1000Ω 
ΝΟ 
0% 
10KΩ 
9.88Ω 
YES 
1.2% 
9000Ω 
YES 
10% 
Table 3.1 Measure the internal resistance of each voltage scale
DMM 
Specified Internal Resistance 
Measured Resistance 
200mV 
10 
10.01 
2V 
10 
9.90 
20V 
10 
9.90 
200V 
10 
10.07 
Table 3.2 Measured internal resistance of DMM’s current scales
DMM 
Measured Resistance 
200μΑ 
955 
2mA 
100.5 
20mA 
11.1 
200mA 
2.2 
2A 
1.1 
20A 
0.6 
Table 4.1 Difference between the DMM set on power supply
Power supply 
DMM 
% Difference 
1V 
0.97V 
3% 
4V 
3.95V 
1.25% 
5.5V 
5.48V 
0.36% 
8.25V 
8.17V 
0.97% 
9.6V 
9.58V 
0.21% 
12.1V 
12.08V 
0.17% 
16.4V 
16.41V 
0.06% 
18.75V 
18.7V 
0.26% 
Table 4.2 R=1 ΚΩ Ohm’s low
Vr (VOM) 
Ir (DMM) mA 
Ir = Vr/Rmeas. mA 
% Difference 
0V 
0mA 
0mA 
0% 
2V 
2mA 
2.04mA 
1.96% 
4V 
4.1mA 
4.08mA 
0.49% 
6V 
6.1mA 
6.12mA 
0.32% 
8V 
8.2mA 
8.16mA 
0.49% 
10V 
10.2mA 
10.2mA 
0% 
Data discussions
On the table 1.2 resistors do not have the accurate values which are recorded on it but it is fluctuated between minimum and maximum values. On table 2.1 seeing the different between normal resistor value and measure value using DMM and VOM. You can see that the DMM is more accurate than VOM although it fount the 1ΚΩ value exactly.
On the table 3.1 seeing that as many different values volts put on the specified internal resistance the difference with the measured resistance are very small. On the table 3.2 seeing that as much ambers put on, so much accurate values have.
On the table 4.1 seeing that the difference between the DMM and the power supply is very small except the lower values among 1v and 4v. On the table 4.2 seeing the difference between the current we found on the DMM and the current we found plotting the Ohm’s law. The different between them is very small except the value of 2v.
Error Analysis
The difference between the normal resistor value and the measure value use the following equation:
(table2.1)
%Difference= NominalMeasured X 100%
Nominal
The difference between the current of DMM values and Ohm’s law current use the following equation:
(table 4.2) %Difference= Ir (DMM)Ir (Ohm’s law) X100% . Ir (DMM)
RECOMMENDATIONS and CONCLUSIONS
On my opinion the best way to measure resistors is by using the DMM. The DMM read resistance, voltage and current with a digital display. It is the faster and most accurate way (table 2.1). The second most accurate way to measure resistance is by using Ohm’s law. It can used when the person has not the actual circuit but the circuit diagram. The third best way to calculate the resistor is the color code. I believe that is not very good way to measure resistor because it takes a long time and you cannot find the exactly value of the resistor but the minimum and the maximum resistance (table 1.2). The least accurate way is using the VOM. On the table 2.1 you can see that VOM’s measure value for the 10KΩ resistor was found 9000Ω so the difference is 10%.
When you measure the internal resistance, do not care about how many volts you are put on because the measure values have little different (table 3.1) but you should be careful when measure it with amperes. I advice you to put big values of ambers because as much amperes you put on, so much accurate values you have (table 3.2).
The difference between the DMM set on the power supply is very small but you should be careful among the values 1v and 4v because the different is 3% and 1.25% corresponding (table 4.1)
The difference between the measure values of IR from the DMM and the measure values of IR using the Ohm’s law is very small (table 4.2).