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A lab experiment to verify ohm's law and measure resistances in series, parallel, and series-parallel combinations using an ohm's law board, dc power supply, voltmeter, and ammeter. Students will take voltage and current readings for individual resistors and resistor combinations to determine resistance values and calculate percent differences.
Typology: Exams
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To measure voltage across a resistor and current through a resistor to verify Ohm's law and to verify the equations for series and parallel combinations of resistors.
APPARATUS: Ohm's Law Board Assorted wire leads DC Power Supply Voltmeter Ammeter
METHOD: Three unknown resistances are measured by taking a series of voltage and current readings for each resistor.
resistance can be determined from the graph. The resistance of the three resistors connected in series is found by taking a sequence of voltage-current readings. The resistance from the slope of the graph may then be compared with the value calculated from the series resistance formula.
PROCEDURE: HAVE AN INSTRUCTOR CHECK ALL CIRCUITS BEFORE TURNING ON ANY POWER SUPPLY
b. Connect the voltmeter across the resistor. Turn on both digital meters. The current control on the power supply should be near its maximum, the voltage control should be at its minimum. Turn on the power supply and adjust it until the voltmeter reading is 2 volts. Record this voltage and its corresponding current reading. d. Take additional readings at 4, 6, 8 and 10 volts. e. Repeat steps 1a through 1d with each of the other two resistors. (R 2 and R 3 ) f. Turn off the digital meters turn the voltage to zero, and then turn off the power supply.
Figure 2
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b. Connect the voltmeter so that it is across all three resistors as shown. Turn on both digital meters. c. Turn on the power supply and take readings for voltage and current, but with voltages of 2, 4, 8, and 10 volts. Record these values on the given data table. d. Turn off the digital meters turn the voltage to zero, and then turn off the power supply.
b. Connect the voltmeter across the parallel combination of resistors. Turn on both digital meters. c. Turn on the power supply and take readings as before for applied voltages of 2, 4, 6, 8 and 10 volts. Record these values on the given data table. d. Turn off the digital meters turn the voltage to zero, and then turn off the power supply.
b. Connect the voltmeter across the series-parallel combination of resistors as shown. Turn on both digital meters. c. Again make measurements for voltage and current with applied voltages of 2, 4, 6, 8 and 10 volts. Record these values on the given data table. d. Turn the voltage to zero, then turn off the power supply and disconnect the circuit. Make sure that all digital meters are turned off.
Parallel: Using Resistor 1, Resistor 2, Resistor 3 data
resistance using: 1 2 3
Record this value on the results table.
Calculate the percent difference using the resistance value from the parallel graph to results above. Record this value on the results table.
Series - Parallel: Using Resistor 1, Resistor 2, Resistor 3 data
equivalent resistance using: 2 3
2 3 (^1) R R
R R Record this value on the results table.
Calculate the percent difference using the resistance value from the series-parallel graph to results above. Record this value on the results table.
RESULTS TABLE: Include Units
Graph Experimental Experimental Percent Difference
Resistor 1 Resistor 2
Resistor 3
Series Parallel
Series-Parallel