UNESCO-NIGERIA UNESCO TECHNICAL & 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 × 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 × 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 × 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 × 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 × 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 ±5% and the gold indicates ±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 ±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 ½ 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, µ (micro), n (nano) and p (pico): • µ means 10-6 (millionth), so 1000000µF = 1F • n means 10-9 (thousand-millionth), so 1000nF = 1µF • 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 ± 5% Resistor R2 = 1KΩ ± 5% Resistor R3 = 220KΩ ± 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 ± 5% Resistor R2 = 1KΩ ± 5% Resistor R3 = 220KΩ ± 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