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Jared Acevedo & Kenny Lim Physics 102 Lab #3: Ohm’s Law February 14, 2006 Abstract The purpose of this lab is to construct a series circuit, a parallel circuit and a combination parallel-series circuit choosing three different resistance values for each resistor while setting the power supply to 6 Volts. Building these different circuits will allow us to verify Ohm’s Law: V=IR. Equipment Voltmeter (digital) Ammeter (digital) Resistors (decade boxes) D.C. Power Supply 6 Connecting Wires Procedure 1. In order to build the first circuit (Series) three resistors (decade boxes) were connected to one another in a series, while the Power Supply was connected to the first resistor and the third resistor in the series. 2. The first resistor was set to 100Ω, the second resistor in the series was set to 200Ω, and the third was set to 300Ω. 3. The Power Supply was turned on and set to 6 volts. 4. The current was measured by replacing a wire from the Voltmeter and set to DCA. 5. The voltage was measured across each resistor. 6. The parallel circuit was made by placing the conducting wires from the Power Supply on one resistor, then on the second, then on the third. 7. Once all wires were connected steps 2-5 were performed.. 8. In order to create a series-parallel circuit the first two resistors were created in a parallel arrangement as above, while the third was placed in series with the other two bulbs. 9. Once all wires were connected steps 2-5 were once again performed Data Please see Excel Spreadsheet for data. Calculations 1. Theoretical current for series circuit V = IR ; I = V/R V = 6V Rtotal = 100Ω + 200Ω + 300Ω = 600Ω I = 6V / 600Ω = 0.01 A 2. Theoretical total resistance and current. V = IR V = 6V 1/Rtotal = (1/100Ω) + (1/200Ω) + (1/300Ω) Rtotal = 54.54 I = 6V / 54.54Ω = 0.11 A 3. Theoretical currents. I = V/R V1 = 2.680V V2 = 3.261V V3 = 3.270V I1 = 2.680V / 100Ω = 0.0268 A I2 = 3.261V / 200Ω = 0.0163 A I3 = 3.270V / 300Ω = 0.0109 A Slope for series circuit graph. Slope = Rise / Run Slope = (2.945 – 2.033) / (300 – 200) = 0.01 Slope is the value for the current. Slope for parallel circuit graph. Slope = (0.10 – 0.02) / [(1 / 54.54) – (1 / 300)] = 5.33 Slope is the value for the voltage Graphs Please see Excel Spreadsheet (chart 1 and 2) for graphs. Error Analysis The weakness in this experiment that can cause an error is some of the equipments we used in the lab and how we handled or used the equipment during the experiment. First of all, errors can occur from the uncertainty of the equipments we used for determining the currents and voltage (digital voltmeter & ammeter). Also connecting wires can cause a little error on current flow due to certain inhibitions. Some of the potential errors can be made by misplacing connecting wires, resistors or equipments to measure the voltage and current. % Error on series voltage = [|6.000V – 6.007V| / 6.000V] X 100 = 0.12% % Error on parallel voltage = [|6.00V – 5.92V| / 6.00V|] X 100 = 1.33% % Error on combination current = [|0.0109A – 0.0100A| / 0.0109A] X 100 = 8.3% Questions 1. What can you say about the sum of the voltage drops in circuit 1? The voltage drops in circuit 1 will add up to approximately the total voltage (6V) as a result of the conservation of energy. In our circuit, V1=1.029 + V2=2.033 + V3=2.945 Vtotal= 6.00. 2. What can you say about the sum of the currents through the resistors in circuit 2? The current sum that enters from point A must equal the total current leaving that point. Therefore the total current must be approximately equal to the sum of the individual currents. In our circuit I1=.05A + I2=.04A + I3=.02A = Itotal =.11A. 3. Construct a graph for each circuit. Look for obvious linear relationships and calculate the slopes of these lines. See Graphs on Excel Spreadsheet. In the series circuit a linear relationship between the slope of Volts vs Ohms or V/R is equal to the current (I) from V=IR. In the parallel circuit, the linear relationship between the slope of Amps vs 1/Ohms or A/(1/Ω) is equal to the total voltage from V=IR. 4. Construct a table, subdivided into three parts, where every experimental value is compared with its theoretical value. See table on Excel Spreadsheet. Conclusion In this experiment, we determined the current and the voltage of the series, parallel and series-parallel combination circuit with the pre-determined resistance value. This is done to study the relationship between the current, voltage and resistance and to prove the Ohm’s law (V=IR). In the series circuit, the current stayed constant and as voltage increases, resistance increased as well. In the parallel circuit, voltage stayed the same so therefore, the current and resistance have an inverse relationship. As the current goes up, resistance goes down. Grade: 98/100