# Resistors, the color code and Ohm’s law

20/07/2013 12:27

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  I-V 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: GDM-8135, Serial Number: CF-922334)

·         Analog Multimeter                  (Brand: HAMEG, Model: HM 203-6, 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 Bands-Color Color bands-Numerical 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= Nominal-Measured 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).