Name __________________________
Period ______ Date _______________
Lab Partners _____________________
V
_____________________
DC Circuits Lab
Purpose: To verify the behaviors of resistors wired in series and parallel circuits by comparing
calculated to measured voltages and currents for three resistors wired first in a series
circuit configuration, then wired in a parallel circuit configuration.
Materials:
 Power supply (or batteries) that can be set to voltages between 3.0 volts and 6 volts
 Three different value resistors ranging from 50 ohms to 500 ohms
 Four wire leads
 Multimeter
Procedure:
Part I – SERIES CIRCUIT
 Read and record the values of the three different resistors you chose in the data table,
including the tolerance (%error) factor for each reading.
 Set the multimeter to read ohms and measure the resistor value for each of the three resistors
you chose, as shown in the diagram below.
Using the
Multimeter
To measure
Resistance
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
Set up a simple series circuit with the power supply connected to the first of your resistors
Set the voltage to somewhere between 3 and 6 volts (or use a single dry cell) and turn the
power supply on
Set the multimeter to read DC Volts at its lowest reading, then turn on the multimeter
Measure and record the voltage across each resistor as demonstrated in class and in the
picture below by:
o touching the positive probe to the side of the resistor leading to the positive
connection at the power source and simultaneously
o touching the negative probe to the side of the resistor leading to the negative
connection at the power source (see diagram on following page)
Using the
Multimeter as
a Voltmeter


Power
source
Measure and record the total voltage for the entire span of three resistors by touching one
probe before the first resistor and the second probe after the third resistor.
Measure and record the current through each resistor. To do so:
o Disconnect the negative end of the resistor from the line and attach it instead to the
positive probe on the multimeter.
o Attach the negative probe of the multimeter to the line.
o Turn the multimeter dial to measure the smallest amount of DC current (DC Amps)
o Turn on the multimeter and record the current measurement, being careful to note the
prefix (milli-, micro-) before the amperage reading.
Using the
Multimeter
to measure
Current






Measure and record the total current for the entire span of three resistors.
Remove the probes from the resistors and turn off the multimeter.
Calculate and record the total resistance expected from reading the resistor band codes.
Calculate and record the total current expected from the power box voltage setting and the
total resistance.
Calculate and record the expected voltage drops for each resistor based on the resistor band
reading and the power source setting.
Compare the calculated to the measured total voltage and current by calculating percent
difference based on the calculated values being the more accurate.
Part II – PARALLEL CIRCUIT
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

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

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
Set up a simple parallel circuit with the same three resistors you used for the series circuit.
Set the voltage to the same voltage you used for the series circuit
Measure and record the voltage drop across each resistor as demonstrated in class
Measure and record the currents through each resistor as demonstrated in class
Measure and record the total voltage across all three resistors together.
Measure and record the total current through all three resistors together.
Calculate the total resistance for the circuit using the resistor band codes.
Calculate the expected voltage drops and individual resistor currents.
Calculate the percent difference between your measured and calculated values for current and
voltage
Questions:
1. Draw a circuit diagram below showing the setup for the series circuit part of this experiment by
using the appropriate circuit symbols. Be sure to include the power source, the resistors, the
ammeter, and the voltmeter in your diagram. Label each device with the appropriate letter.
2. Draw a circuit diagram below showing the setup for the parallel circuit part of this experiment
by using the appropriate circuit symbols. Be sure to include the power source, the resistors,
the ammeter, and the voltmeter in your diagram. Label each device with the appropriate letter.
3. According to your lab results, what relationship exists between the total voltage and the
individual voltages through each particular resistor when the circuit was:
Series:
Parallel:
4. According to your lab results, what relationship exists between the total current and the current
through each resistor when the circuit was:
Series:
Parallel:
5. According to your lab results, which resistor put out the most power (biggest or smallest
resistor) when in:
Series:
Parallel:
6. What would happen if the total voltage in each circuit was not used up by the resistors?
7. What happens if you use the multimeter as a voltmeter when you have it set as an ammeter?
8. Should the voltmeter have a high or a low resistance? Why?
9. Should the ammeter have a high or a low resistance? Why?
Data Table:
Power Box Voltage Setting : ________
Resistor 1 colors____________
____________ ____________
+/-color band __________
Resistor 2 colors____________
____________ ____________
+/-color band __________
Resistor 3 colors____________
____________ ____________
+/-color band __________
SERIES CIRCUIT
Quantity
R1 code value
Calculated
Measured
% Error
R2 code value
R3 code value
Total Current
Total Voltage
Voltage R1
Voltage R2
Voltage R3
Current I1
Current I2
Current I3
PARALLEL CIRCUIT
Quantity
R1 code value
R2 code value
R3 code value
Total Current
Total Voltage
Voltage R1
Voltage R2
Voltage R3
Current I1
Current I2
Current I3
Calculated
Measured
% Error
Quantity
Series Rtotal
% Error
Rmeasured versus
Rcalculated
Itotal
Series
Series Vdrop
R1
Series Vdrop
R2
Series Vdrop
R3
% Error
Imeasured versus
Icalculated series
% Error series
V TOTAL (meas)
versus
V TOTAL (calc)
Parallel Rtotal
Itotal
Parallel
Parallel I1
Parallel I2
Parallel I3
% Error parallel
I TOTAL (meas)
versus
I TOTAL (calc)
Formula
SAMPLE CALCULATIONS
Substitution
Answer with Units