EMT1150_Lab4 - Ohm Law(2)

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EMT1150 Lab Manual (08/2020) 1 EMT1150 Lab Experiment 4 Ohm’s Law Measurements Objective: Build circuits on breadboard, correctly measure voltage and current of certain circuit components. Understand the applications of Ohm’s law in different formats. Part A 4.1 Build circuits on breadboard 4.1.1 Breadboard An electronics breadboard is actually referring to a solderless breadboard. These are great units for making temporary circuits and prototyping, and they require absolutely no soldering. For those new to electronics and circuits, breadboards are often the best place to start. That is the real beauty of breadboards–they can house both the simplest circuit as well as very complex circuits. The primary function of breadboard circuit is to test or prototype certain circuits. You can easily make modifications on breadboard circuits based on your results. Another common use of breadboards is testing out new parts, such as Integrated circuits (ICs). When you are trying to figure out how a part works and constantly rewiring things, you don’t want to have to solder your connections each time. A typical breadboard is shown in Figure 4.1(a). On the top view, a breadboard is a very simple plastic block with holes onto which circuit elements are plugged in and interconnected. If the bottom part of a breadboard is removed, you can see lots of horizontal rows of metal strips on the bottom of the breadboard as shown on Figure 4.1(b). The tops of the metal rows have little clips that hide under the plastic holes as shown in Figure 4.1(c). These clips allow you to stick a wire or the leg of a component into the exposed holes on a breadboard, which then hold it in place. As shown in Figure 4.1(a) and (b), on each long side, one is identified with a red line (labeled with a +), and one with a blue line (labeled -). All the holes in each long line of holes are connected together underneath the board. Each line of connection is known as a node. In other words, there is a short circuit between any two holes on any long outside line that is identified with red or blue. These two lines are usually connected to power supply. In the middle (running the long way), there is an indentation in the board. This indentation separates the two halves of the board. Each row of 5 holes on either side of the indentation is a node. If you put a circuit component on the same row, that is a short connection , which will cause problem in a circuit.

EMT1150 Lab Manual (08/2020) 2 4.1.2 Power supply Any functioning circuits need to have a power source. In a regular lab setup, you can use a DC power supply as shown in Figure 4.2(a) which can supply up to three adjustable DC voltages. However, we have to practice labs in the home setting, the power supply in the lab kits is a 9V battery with clip connector as shown in Figure 4.2(b). (a) (b) (c) Figure 4.1. Breadboard structure (a) (b) Figure 4.2. Power supply

EMT1150 Lab Manual (08/2020) 3 4.1. 3 Build a resistive circuit on breadboard Here demonstrate a simple way to connect a simple circuit with one resistor and one switch on breadboard, Figure 4.3. There are different ways to build and make connections among the elements within the circuit. One way to do so is by the order of the elements: Circuit Schematic Description Protoboard Connection To build the circuit, we need to place the switch first. Put the middle leg of the switch in a node 5 and Row H, which needs to be connected to “+”.The right leg of the switch needs to be connected to one side of R1. So put a jumper wire in a hole of “+” and in a node 5 and Row J. And put another wire between nodes 6 and 13 of Row F. It should be OFF when you slide the button to the left and ON when the button to the right. Switch: OFF Switch: ON Figure 4.3 Build a simple circuit

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EMT1150 Lab Manual (08/2020) 4 4.2 Measure voltage and current on a breadboard circuit We practiced how to measure resistance using Multimeter in Lab 3. Remember the resistor is always isolated from any power supply when measuring resistant. Multimeter can also measure voltage and current in a circuit, but the measurement procedures are different in a certain way. 4.2.1 Measure voltage using Multimeter Before placing the testing probes in the circuit to measure voltage, you have to set your Multimeter to measure voltage. To set up the Multimeter, make sure that the red probe is connected to the VΩ socket and the black probe to the COM socket as shown in Figure 4.4(a) Once the Multimeter is set up to measure voltage, the next step is to measure the voltage across a component in the circuit. Once the circuit is power, you can place the Multimeter leads across the component whose voltage you want to measure as shown Figure 4.4(b). Place R1 between nodes 13 and 22 of Row H. Connect the other side of R1 to the Ground.

EMT1150 Lab Manual (08/2020) 5 This technique is applied because voltage is the potential difference between two points. It is also good to remember that to measure the voltage across a component, the Multimeter has to be in parallel to the measure component. 4.2.2 Measure current using Multimeter To set up the Multimeter, make sure that the red probe is connected to the mA socket and the black probe to the COM socket. Measuring current is more complicated than measuring resistance or voltage. There are two main reasons for this: 1. The connection of the Multimeter with the measure component. In order for the Multimeter to measure the current through a component, the Multimeter has to be connected with the measure component in a way that the current can go through the Multimeter and the component. This means that the Multimeter must be made part of the current path of the circuit. In order to make the Multimeter part of the current path of the circuit, the original circuit must be “broken” and the meter connected across the two points of the open break. When the Multimeter is part of the open break, the Multimeter is connected in series with the measure component. 2. The fuse of the Multimeter. One of the most common mistakes with the use of the Multimeter to measure current is to connect the probes in parallel with the measure component. This will immediately short power to ground through the Multimeter causing the power supply current going through the Multimeter. As the current rushes through the Multimeter, the internal fuse (a) (b) Figure 4.4 Measure Voltage Figure 4.5 Measure Current

EMT1150 Lab Manual (08/2020) 6 will heat up and then burn out as 200 mA flows through it. Remember that a fuse is a safety device consisting of a strip of wire that melts and breaks if the current exceeds a safe level. A burned fuse can be replaced in the Multimeter by opening the back cover of the Multimeter. Part A Lab Experiment Procedure Exercise 4.1 1. Use Multisim to simulate the following circuit, measure the voltage and current of 1kΩ resistor in Multisim. Input your data to table1 2. Construct a circuit in Figure1 on breadboard, use Multimeter to measure the voltage and current. Record your data in Table1. Table 1 Multisim Breadboard V R1 I R1 Question: What is your conclusion between those measurements? V1 9V R1 1kΩ Figure 4.6 Exercise 4.1

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EMT1150 Lab Manual (08/2020) 7 Exercise 4.2 1. Test switch: The switch in your package is a SPDT (single pole double throw switch). Use the continuity function of Multimeter to check how the switch works. 2.Construct the following circuit, let the switch in the open position . 3. Measure the voltage at the source and voltage at the resistor, R1 and R2. Remember to connect the Multimeter in parallel position when measuring the voltage. Record the data in Table 2. Table 2 Voltage Source R1 R2 Switch open Switch close 4. Close the switch , measure the voltage of source and resistors again. Record data in Table2. V1 R1 1kΩ S1 Key = Space R2 330Ω Figure 4.7 Exercise 4.2 9V V1 R1 1kΩ S1 Key = Space R2 330Ω 9V

EMT1150 Lab Manual (08/2020) 8 5. Connect the Multimeter to measure the current of circuit. Remember to connect the Multimeter in series when measuring the current. Read the current when the switch is open, then read the current when switch is closed. Record data in Table 3. Table 3 Current Source R1 R2 Switch open Switch close Question: Conclude the function of switch in this circuit. Exercise 4.3 1. Connect a circuit in Figure 4.8. Start with arrange resistors on proper position, then connect the wires. Use Multimeter to measure voltage for source and R1, R2, and R3. Use Multimeter to measure current for source and R1, R2, and R3. Record data in Table4. Table 4 Source R1 R2 R3 V I V1 R1 330Ω R2 47Ω R3 1kΩ S1 Key = Space Figure 4. 8 Exercise 4.3 9V

EMT1150 Lab Manual (08/2020) 9 Part B 4.3 Ohm’s Law Ohm’s law describes the relationship among Voltage (V or E), Resistance (R) and Current (I). Knowing any two of the values, the third value may be computed. There are three expression of Ohm’s law. I V R or IR V R V I = = = , , where I has unit of Amper (A ), V has unit of Voltage (V), and R has unit of Ohm (Ω). From Ohm’s law, the relationship between the current and voltage through a resistor is a linear response. This means that the slope of the line is the value of the resistance. Circuit 4.9 shows a 2.2 k Ω resistor connected across a 9-volt battery. Using Ohm’s law, the current can be calculated to be 4.09 mA. mA k R V I 09 . 4 2 . 2 9 = Ω = = Figure 4. 9 S1 Key = Space V1 9V R1 2.2kΩ

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EMT1150 Lab Manual (08/2020) 10 Part B Lab Experiment Procedure Exercise 4.4 1. Build the following circuit in Multisim. Close the switch, measure the current through R1, Record data in Table5. 2. Decrease the output of power supply to 8V, 4V, 2V, and 1V. Measure the current through R1 accordingly. Record data in Table 5. Table 5 E (V) I(mA) R=E/I (Ω) P=EI (mW) Multisim 1 2 4 8 9 Breadboard 3. Build the same circuit on breadboard, measure the voltage and current on R1, record data In Table 5. Measure the resistance R1 using Multimeter directly. 4.Calculate the resistance R and Power P using the measured values. Show calculation procedure in your lab report. Question: Do Multisim simulation and breadboard experiment get the same results? If not, try to explain why? Figure 4. 10 Exercise 4.4 E 9V R1 220Ω S1 Key = Space

EMT1150 Lab Manual (08/2020) 11 Exercise 4.5 1. Build the following circuit in Multisim. Close the switch, measure the current through R1, Record data in Table6. 2.Decrease the output of power supply to 8V, 4V, 2V, and 1V. Measure the current through R1 accordingly. Record data in Table 6. Table 6 E (V) I(mA) I=E/R (mA) P=EI (mW) Multisim 1 2 4 8 9 Breadboard 3. Build the same circuit on breadboard, measure the voltage and current on R1, record data In Table 6. Measure the resistance R1 using Multimeter directly 4.Calculate the Current I and Power P using the measured values. Show calculation procedure in your lab report. Question: Do Multisim simulation and breadboard experiment get the same results? If not, try to explain why? Figure 4.11 Exercise 4.5 E 9V R1 470Ω S1 Key = Space

EMT1150 Lab Manual (08/2020) 12 Exercise 4.6 1. Build the following circuit in Multisim. Close the switch, measure the current through R1, Record data in Table7. 2.Decrease the output of power supply to 8V, 4V, 2V, and 1V. Measure the current through R1 accordingly. Record data in Table 7. Table 7 E (V) I(mA) V=IR(V) P=EI (mW) Multisim 1 2 4 8 9 Breadboard 3. Build the same circuit on breadboard, measure the voltage and current on R1, record data In Table 7. Measure the resistance R1 using Multimeter directly 4.Calculate the Voltage V and Power P using the measured values. Show calculation procedure in your lab report. Question: Do Multisim simulation and breadboard experiment get the same results? If not, try to explain why? Figure 4.12 Exercise 4.6 E 9V R1 1kΩ S1 Key = Space

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EMT1150 Lab Manual (08/2020) 13 Questions: 1) In each table compare the current and voltage. From these readings, what can you say about the relationship between the current ( I) and applied voltage ( E) when the resistance ( R) remains constant? 2) In Tables5-7, compare the currents for E = 4V. What do you deduce about the relationship between the current I , and the resistance R , when the applied voltage E remains constant? 3) From the information contained in the tables, what happens to (a) the current and (b) the power dissipated, if the voltage is doubled and the resistance remains constant? 4) From the information contained in the tables what happens to (a) the current and (b) the power dissipated, if the voltage is halved and the resistance remains constant? 5) On a Graph, plot all the points E and I in Multisim simulation for each resistor. 6) On a Graph, plot the all points of R and I in breadboard data. ----------- L AB E XPERIMENTS E NDS H ERE , P ROCEED W ITH L AB R EPORT -----------------