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Circuit Lab Name _______________________________ OBJECTIVES: To be able to make series and parallel circuits when given wires, resistors, and a voltage source. To draw a circuit diagram using appropriate symbols. To relate voltage and current in a series and parallel circuit and draw conclusions about each type based on recorded data. EQUIPMENT: o o o voltage source (batteries) breadboard multimeter o o o 3 different resistors connecting wires (4 with alligator plugs, 2 without) calculator THEORY: An electrical circuit is a complete path of conducting materials that allows electrical current to flow. The two main types of circuits are series and parallel circuits, both of which have distinct characteristics and are used according to the desired function of the circuit and its elements. A series circuit may be thought of as a one-way circuit. The current that enters the path is the same amount of current that must leave each point of the path. A parallel circuit on the other hand offers different routes through which the current may follow. More current will flow through the path of least resistance. PART 1; Setting up the breadboard: to To the right is a schematic diagram of the breadboard. As you can see, each vertical row of five points is electrically connected, and the horizontal points are electrically connected as far as the center mounting screws. We must connect the breadboard itself to the red and black power supply terminals above it. 1. Take the short wires without alligator clips connected to them, and place one end in a section in the upper right-hand corner of the board. 2. Unscrew one of the red terminals, place the other end of the wire in the hole in the terminal, and tighten the terminal again. 3. Connect the second small wire between the black terminal and a section in the lower right hand corner of the board. Terminal Posts to Vertical Points Horizontal Points The circuits you build must begin and end at the sections these two wires are connected to. In order to use the breadboard, we must connect it to a power supply. We will use two 1.5 V '"D" cell batteries as our power source. 1. Connect the red post to the (+) terminal of the first battery. 2. Connect the black post to the (-) terminal of the second battery. 3. The two batteries then must be connected together with a wire going from the negative of the first to the positive of the second. (If you are using the blue battery holders, you do not need this final wire to connect them.) REMEMBER: To measure current, the multimeter must be connected in series with the circuit. To measure voltage, the multimeter must be connected in parallel. 1 + - PART 2; Resistance Measurement PROCEDURE: 1. Locate 3 resistors with various color codes. 2. Record the colors of the resistors in the table below starting with the color opposite the gold band. 3. Determine the resistance of each resistor from the above table. Resistor # First Color Second Color Third Color Resistor Value (Ohms) R1 R2 R3 4. Now measure the value of the resistance with the multimeter. You MUST make this measurement BEFORE the resistors are placed into any circuit or you will not get the correct readings! To the right is a picture of the multimeter with the segments labeled that you will be using: Turn the mulitmeter to the area (probably the 200 setting) and hold the probes on each end of the resistor to measure the resistance. Compare your measured value to the color code value by finding the absolute value. Resistor # Color Code Value Measures Voltage Measures Current Measures Resistance Measured Value Absolute Error R1 R2 R3 PART 3: SERIES CIRCUIT: 1. Connect 3 resistors in a series circuit. Remember that the end of one resistor must be placed in a line of openings that is connected with the beginning of the next resistor. The wires should just fit down inside the openings. You will have to bend the resistors to connect them. 2. Draw a circuit diagram to the right to represent your circuit. Label each resistor Rl, R2, and R3. 3. Connect your voltmeter over the entire circuit. Do this by placing the positive clip on the first resistor wire BEFORE the actual resistor, and placing the negative clip on the last resistor AFTER the actual resistor. Record what the total voltage is coming from your batteries below: TOTAL VOLTAGE = ____________ V 4. Complete the data table by taking measurements with the multimeter. 2 (Place the MEASURED resistance value from the previous section in the table) To take the measurement of voltage, you will need to hold both probes on either end of the resistor while it is in the circuit. Don’t forget to turn your multimeter over to the “DCV” (probably 20) setting. To take the current measurements, take one of the ends of the resistor you are measuring out of the circuit and place a probe on that end. Place the other probe on the next wire or resistor to which the one you removed would normally be connected. Don’t forget to place your mulitmeter on the “DCA” (probably 20 m) setting. The pictures below depict how to make the measurements: TO MEASURE VOLTAGE Resistor # TO MEASURE CURRENT: Current (mA) Resistance () Voltage (V) R1 R2 R3 Total= Avg= Total= Questions: 1. What do you notice about the current through each resistor? 2. Comparing the total voltage and the voltage of the source, what can be said about these values? 3. Using Ohm's law and the average current and voltage through each resistor, calculate the resistance of each resistor and fill it in on the next data table. Compare this value to the color-coded value by finding the absolute error: Resistor # R1 Color Code () Calculated () R2 R3 PART 4: PARALLEL: 3 Absolute Error 1. Disconnect the power supply before changing your circuit. You will have to reconnect it once you are done. Connect 3 resistors in parallel with the power source. 2. Draw a circuit diagram to represent your circuit. Be sure to include labels for the resistors. 3. You will once again measure voltage and current. Your resistance is once again the values you measured in Part II of the lab before you put the resistors in a circuit. Below are two pictures that describe how to measure current and voltage in this circuit. NOTE: when measuring current, you still want to remove one end of the resistor and then measure between it and the red wire supplying it. Keep the red wire in the breadboard so that the current is still supplying the rest of the circuit, otherwise you will not get a true reading of the amount of current through that resistor. TO MEASURE VOLTAGE: Resistor # R1 TO MEASURE CURRENT: Current (mA) Resistance () Voltage (V) R2 R3 Total = Total = Average = Measured value of power supply = __________ V BE SURE TO DISCONNECT YOUR CIRCUIT COMPLETELY SO THAT THE BATTERIES ARE NOT DRAINED!!!!!!!!! Questions: 1. Compare the voltage across each resistor to the voltage across the power source. How do they compare? 4 2. Calculate the % error using the measured as the accepted. 3. In a Series circuit (circle answers): a. The voltages across each resistor (adds up to / is the same as) the voltage of the power supply. b. The current through each resistor (is less than / if the same as) the total current entering the circuit. 4. In a parallel circuit (circle answers): a. The voltages across each resistor (adds up to / is the same as) the voltages across the power supply. b. The current through each resistor (is less than / is the same as) the total current entering the circuit. 5. Ohm's law states that current is given by the ratio of voltage/resistance. In what way does your data concur or not concur with this? BE SURE TO DISCONNECT YOUR CIRCUIT COMPLETELY SO THAT THE BATTERIES ARE NOT DRAINED!!!!!!!!! 5