EMNG1001_Lab8_RC-Circuits_InClass(2)

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George Brown College Canada *

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EMNG1001

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Electrical Engineering

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Dec 6, 2023

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docx

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Student First Name: Karma Student Last Name: Jangchup Student Number: 101494666 Submission Date: 24/11/2023 General Notes: 1. Type your name, student ID, and the submission date of the lab in the above fields. 2. Practice safety at all times. Carefully follow the directions of the lab. Do not use broken power cords or broken devices powered directly from the mains such as the DC supply. 3. Use only the electronic kit and devices provided by George brown college. Also, ensure that all equipment in the kit stays in good working condition. 4. Carefully read and follow ALL lab instructions provided in the lab write-up. 5. Complete all measurements, calculations, tables, drawings, and images required for all labs. 6. Answer all questions neatly and concisely in the spaces provided (preferably in bold red). 7. All Labs must be submitted by their due dates in Blackboard and cannot be made up. A grade of “Zero” will be assigned for missed labs. 8. The mark and possible feedback will be posted in Blackboard after the due date of each lab. Submission: This original word document with answers included in full is required to be submitted in Blackboard by the due date. It is not allowed to submit another separate document that includes only answers to the questions. Lab 8 RC Circuits Objectives Upon completion of this lab students will be able to: 1. Identify and describe the main characteristics of capacitors. 2. Use the digital multimeter to perform simple capacitor tests. 3. Construct simple RC circuits. 4. Use LEDs to provide a visual indication of the charge and discharge cycles of RC circuits. 5. Describe and verify the charging and discharging cycles of RC circuits. Introduction A capacitor is formed whenever two conductors are separated by an insulating material which is called a dielectric. When a voltage is present between the conductors, there will also be an electric charge Ali A. Hussein, Ph.D., P. Eng. EMNG 1001, Circuit Analysis Lab Page 1 EMNG1001 Circuit Analysis Lab 8 RC Circuits

between the conductors. The ability to store an electric charge is a fundamental property of a capacitor. A capacitor’s ability to store charge is directly proportional to the area of the plates and inversely proportional to the plate separation. The amount of charge stored by a capacitor is given by the following equation: Q = CV where Q is the charge in Coulombs, C is the capacitance in Farads, and V is the voltage in Volts. Recall that current is defined as the amount of charge per time I = Q / T . Hence; Q = IT where I is the current in Ampers, and T is the time in seconds. When two capacitors are connected in series, the same current flows through both capacitors for the same amount of time. Hence; Q 1 = Q 2 → V 1 V 2 = C 2 C 1 where Q 1 ( Q 2 ) and V 1 ( V 2 ) are the charge and voltage, respectively, of the capacitor C 1 ( C 2 ). For this reason, the capacitor with the larger capacitance value will take a smaller voltage than the one with the smaller capacitance value. In a series circuit of N capacitors the total capacitance decreases with the addition of more series capacitors and is found by the following equation: C T = [ 1 C 1 + 1 C 2 + … + 1 C N ] − 1 In a parallel circuit of N capacitors the total capacitance increases with the addition of more parallel capacitors and is found by the following equation: C T = C 1 + C 2 + … + C N The ohmmeter function of the multimeter can be used to check the capacitor before using it in constructing a circuit. The ohmmeter test can be done as follows: a. At first, make sure the capacitor is fully discharged. This can be easily done by shorting the leads of the capacitor for a moment. b. Set the ohmmeter to a very high resistance scale and connect the ohmmeter to the capacitor leads. Make sure the polarity is correct; i.e. the positive (negative) lead of ohmmeter is connected to the positive (negative) lead of the capacitor. c. At the moment the ohmmeter is connected to the capacitor leads, the ohmmeter should start changing its reading ideally from a very small resistance to a very large resistance aiming to infinity (i.e. open circuit). This indicates that the capacitor is in good condition. d. The charging time of the capacitor depends on the RC time constant of the resulted circuit. So for large capacitances, you may have to decrease the ohmmeter setting to a lower resistance range to speed the counting process. For small capacitances, the counting process is so quick that you might not be able to observe it, so in such a case you have to set the ohmmeter to the available maximum resistance range. For this reason, testing small capacitances is harder than testing large capacitances. If you notice that the ohmmeter display flickers on the testing of a small capacitance (i.e. it changes its displayed number so quick on contacting the capacitor leads), Ali A. Hussein, Ph.D., P. Eng. EMNG 1001, Circuit Analysis Lab Page 2

then that could be considered as enough indication that the capacitor is good. However, if the display of the ohmmeter never changes showing the symbol of infinity before and after connecting the small capacitance, then that would indicate the ohmmeter test has failed. This does not necessarily mean that the small value capacitor is bad in this case. Instead, other different methods may be utilized to verify the validity of the capacitor. e. When conducting the ohmmeter test, the resistance should never remain near zero as this indicates a capacitor short. On the other hand, an immediate high resistance reading, particularly for larger capacitors, indicates an open circuit. The two simple steps of the ohmmeter test are explained in Figure 1 below. Figure 1 Two steps of the ohmmeter test. Part 1 Procedure 1. Obtain five capacitors from your toolbox as listed in Table 1. Use the DMM to perform the ohmmeter test as explained in the Introduction section of the lab. Base on your observation indicates the result of the testing of each capacitor (pass or fail) in Table 1. Table 1 Ohmmeter test results. Capacitor Capacitance Value (µF) Ohmmeter Test Result (Pass/Fail) C 1 100 Pass C 2 47 Pass C 3 10 Pass C 4 0.1 Pass C 5 0.01 Pass 2. Construct the circuit shown in Figure 2 on the prototype board. Adjust the DC power source to 12 V. For the switches, S 1 and S 2 , use the push button switches provided in the toolbox. The push- button switch is normally-opened (OFF status), and it is turned ON when you hold press the button. The LEDs (LED 1 and LED 2 ) are polarized components, so the anode and cathode of each Ali A. Hussein, Ph.D., P. Eng. EMNG 1001, Circuit Analysis Lab Page 3

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