LABORATORY Experiment 1

Size: px

Start display at page:

Download "LABORATORY Experiment 1"

August Chandler
6 years ago
Views:

1 LABORATORY Experiment 1 Resistivity Measurement, Resistors and Ohm s Law 1. Objectives To measure the resistance of conductors, insulators and semiconductor and calculate the resistivity of a copper wire. To practice the reading the color band values of resistors To understand the implications of Ohms Law To examine an example of non-ohmic resistance - the diode 2. Apparatus and Components 1. D.C. Power Supply ( x 1) 2. Digital Multimeter (Fluke) ( x 2) 3. Analog Multimeter ( x 1) 4. DC Power Supply ( x 1) 1. Copper Wire 2. Diode IN4148 ( x 1) 3. Resistors of assorted values ( x 10) 4. Resistors 10K ( x 8) Bread board ( x 1) 3. Background 3.1 Resistivity of Materials For various materials, we may study their characteristics in different aspects, including chemical properties, physical properties, mechanical properties and electrical properties. In this experiment, the student is expected to study the major electrical properties of some common materials. Basically, the resistivity is a common parameter to measure how conductive the material is. Generally, the conductive material has a very low resistance of (mω) order. On the contrary, an insulating material has a very high resistance of tens of (MΩ). By definition, the resistivity of a conductor is given as below: Laboratory Experiment 1 1

2 L R =ρ (Equation 1) A EEE3404 Electrical Engineering Principles I where R= resistance, Ω ρ= resistivity of the material, Ω-cm L= length of the conductor A= cross-sectional area of material 3.2 Ohms Law The most fundamental relationship of circuit theory is Ohm s law. Ohm s states that in a purely resistive circuit, current is directly proportional to voltage and inversely proportional to the resistance. There are three ways to express Ohm s Law, namely, I V R V IR R V =, =, = (Equation 2) I where R = resistance, Ω I = current, A V= voltage, V with each form represent a different circuit configuration. We only study the third form R=V/I here. The symbol R, in R = V/I, may represent: i. a passive resistive component, or ii. a collection of several connected resistive components iii. a phenomenon that exhibits linear V/I relationship 3.3 Color Coding of Resistors Small resistors, the kind that you encounter most often in electronic products, are too small to have their values printed on the components. Instead, these smaller resistors are usually covered by an epoxy or similar insulating coating over which several colored bands are 2 Experiment 1 Laboratory

3 printed radially as shown in Figure 1. The first two bands represent the first and second digits of the resistance values. The third band is called the multiplier band and represent the number of zeros following the first two digits; it is usually given as the power of ten. The fourth band indicates the tolerance of the resistor, and the fifth band (if present) is an indication of the expected reliability of the components. Figure 2 lists the colors of the various band and the corresponding values. Figure 1 - Resistor Color Codes Figure 2 - Resistor Color Codes 4. Procedure 4.1 Resistivity of Different Material Use the Multimeter to measure the resistance of the following materials and tabulate into the table below. - + Material under tested - + Material under tested Polarity 1 Polarity 2 Figure 3 Bi-directional Ohmic Measurement Laboratory Experiment 1 3

4 Table 1 Results of measured resistance of materials MATERIAL RESISTANCE ( Ω ) Polarity 1 Polarity meter of #17 Enamel Copper wire (unscraped) 2. 1 meter of #17 Enamel Copper wire (scraped) 3. PVC (plastic rod) 4. Electrolytic Capacitor 100µF (use AMM) Remarks: 1. AMM = Analogue Multi-Meter 2. DMM = Digital Multi-Meter 3. Unless specified, all resistance measurement is performed with DMM 4.2 Resistance Color Code and Measurements Refer to the 10 color coded resistors given to you. Determine the resistance value and the corresponding tolerance for each resistor and enter your results in Table 2. Then you measure each resistor value with a DMM, and complete the Measured column. Table 2 Measured resistance of resistors Color Codes Expected Measured Example Brown Black Orange Gold 10 KΩ ±5 % 9.98 KΩ R1 R2 R3 R4 R5 R6 R7 R8 R9 R10 4 Experiment 1 Laboratory

5 4.2 Application of Ohm s Law In the resistor network of Figure 5, all R s are equal to 10K. Simplify the resistor network to the equivalent circuit as shown in Figure 4. Determine the equivalent resistance by applying a 1V source and measure the current flowing into terminals AB. R AB represents the resistance network. I =? 1 V R AB Figure 4 Equivalent circuit of resistor network Figure 5 Resistor network I AB = R AB = (Measured) (Measured) Laboratory Experiment 1 5

6 5. Discussion 1. Explain the use of Ohm s Law and list its limitations. 2. Explain why there are no perfect insulators in theory and in practical application. 3. What is an ohmic device. 4. Is the diode used in the experiment a good conductor or a good insulator? Explain your answer. 6 Experiment 1 Laboratory

Pre-Laboratory Assignment

Pre-Laboratory Assignment Measurement of Electrical Resistance and Ohm's Law PreLaboratory Assignment Read carefully the entire description of the laboratory and answer the following questions based upon the material contained