Name _________________________________________ Period ___________
BUILDING SERIES AND PARALLEL CIRCUITS
WIRING DIRECTIONS
Materials per group: two D-cells and holders, three lightbulbs and holders, six pieces of insulated wire with stripped
ends
1) Below are diagrams showing three bulbs in series and in parallel. Build these same circuits using two 1.5-volt
D-cells (flashlight-type), three bulbs, some wire with stripped ends. Connecting wires through springs in a
circuit board will help you keep your wiring in place.
2) Record how the brightnesses of the bulbs in the series and parallel circuits change as you increase the bulbs
in the circuits from one to two to three.
SERIES CIRCUIT
PARALLEL CIRCUIT
Note: Your homemade circuits, especially the parallel circuits, will look quite a bit different from the neat rectangular
diagrams shown above.
QUESTIONS
1) Which bulbs are brighter?
a. The three bulbs wired in series.
b. The three bulbs wired in parallel.
c. They're the same.
2) What happens to the brightness as you add bulbs in series?
a. The bulbs get brighter.
b. The bulbs get dimmer.
c. The bulbs stay the same.
3) What happens to the brightness as you add bulbs in parallel?
a. The bulbs get brighter.
b. The bulbs get dimmer.
c. The bulbs stay the same.
4) What do you think these lighting differences suggest about the voltage across the bulbs in series circuits?
a. The voltage across each bulb is less each time a similar bulb is added.
b. The voltage across each bulb is more each time a similar bulb is added.
c. The voltage across each bulb stays the same each time a similar bulb is added.
5) What do you think these lighting differences suggest about the voltage across the bulbs in parallel circuits?
a. The voltage across each bulb is less each time a similar bulb is added.
b. The voltage across each bulb is more each time a similar bulb is added.
c. The voltage across each bulb stays the same each time a similar bulb is added.
USING METERS
BACKGROUND
Voltmeters are connected across the device whose
voltage you wish to determine. One wire is connected
to the positive end of the voltmeter and the positive
side of the power source (battery) or other device
(lightbulb, resistor, motor, buzzer, etc.). The other wire
is connected to the negative end of the voltmeter and
the negative side of the power source or other device.
Basically, you are wiring the voltmeter in parallel with,
or across, the device.
Voltage is measured with a closed circuit so that
current is flowing through the device.
Ammeters are connected in series with the circuit whose current
you wish to determine. (Remember that the same current runs
through all devices in a series circuit.) One wire from the
ammeter is connected to the positive terminal of the power
source (battery, solar cell, etc.). The other wire is connected to
the negative terminal of the power source. Current is measured
with a closed circuit so that current from the battery is flowing
through the circuit.
Series Circuit Using Meters
1) Connect the three light in series.
2) Use the voltmeter to find the voltage drop across each light and the two batteries
Voltage Drop across
Voltage Drop across
Voltage Drop across
Light 1 (V)
Light 2 (V)
Light 3 (V)
Voltage Drop across
Two Batteries (V)
3) Find the total voltage drop across all three light by adding the three voltage drops together.
Total voltage drop: _________________ V (This should be equal to the voltage drop across the two
batteries)
4) Now connect the ammeter in series in the circuit and find the current through the lights.
Current through the lights in A: _________________ A
5) Calculate the resistance of each light using the voltage drop for each and the current.
Resistance of Light 1 (Ω)
Resistance of Light 2 (Ω)
Resistance of Light 3 (Ω)
Parallel Circuit Using Meters
1) Connect the three light in parallel.
2) Use your measured values of the resistance of each light from the activity above to calculate the total
resistance of the parallel circuit.
Total resistance of the parallel circuit: _________________Ω
3) Now calculate the total current through the circuit using the total resistance of the parallel circuit from part 2
and the voltage drop across the two batteries from the activity above.
Calculated total Current through the lights: _________________ A
4) Use the ammeter to find the current through each light. The ammeter must be put in series which each light
to determine the current as shown in the figure below.
Current through Light 1 (A)
Current through Light 2 (A)
Current through Light 3 (A)
5) Find the total current though all three light by adding the three currents together.
Measured total Current: _________________ A
6) Compare the calculated total current from part 3 to the measured total current in part 5 by finding a percent
difference.
Percent Difference: _____________%
Circuits Assignment
Use the following situation to answer problems 1-8. Two
students are studying circuits and how they behave by using
batteries, a lightbulb, a resistor, a voltmeter and an ammeter.
They study the relationship between current, voltage and
resistance in a circuit in Ohm’s Law: V = IR. One student reads
that a component is nonohmic if its resistance changes as a
function of current. If a component is ohmic then as the current
changes the resistance would stay the same and by plotting a
Voltage-Current graph of data, the slope would represent the
resistance and it would be constant. If the Voltage-Current
graph did not have a constant slope then this would imply the
resistance changes with current and the component is
nonohmic.
The students decide to test to see if the lightbulb and the
resistor are ohmic. They connect a voltage source and the
resistor in series and measure the voltage drop across the
resistor and the current through the circuit. (See image to the
right.) They then increase the voltage and take the measurements again. They repeat this four more times. They
then repeat the experiment but this time they replace the resistor with the lightbulb. Their data is shown in the
tables below.
Lightbulb
Voltage (V)
0.10
0.25
0.50
1.0
1.5
2.0
Resistor
Current (A)
0.0052
0.0316
0.061
0.086
0.110
0.134
Voltage (V)
0.10
0.25
0.50
1.0
1.5
2.0
Current (A)
0.00024
0.00069
0.0014
0.0030
0.0045
0.0061
1) Make a graph of the Voltage vs Current for both the lightbulb and the resistor.
LightBulb: Voltage-Current Graph
2
1.8
1.6
1.4
1.2
1
0.8
0.6
0.4
0.2
0
0
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
0.09
0.1
0.11
0.12
0.13
0.14
Resistor: Voltage-Current Graph
2.5
2
1.5
1
0.5
0
0
0.001
0.002
0.003
0.004
0.005
0.006
0.007
2) Review the introduction information and the lightbulb: Voltage-Current Graph and determine if the lightbulb
is ohmic or nonohmic.
a) Ohmic
b) Nonohmic
3) Describe how you are able to determine if the lightbulb is ohmic or nonohmic using the Voltage-Current
graph.
4) What happens to the resistance of the lightbulb as greater currents pass through it as shown on your graph?
a) The resistance increases
b) The resistance decreases
c) The resistance stays the same
5) Review the introduction information and the resistor: Voltage-Current Graph and determine if the lightbulb
is ohmic or nonohmic.
a) Ohmic
b) Nonohmic
6) Describe how you are able to determine if the resistor is ohmic or nonohmic using the Voltage-Current
graph.
7) What happens to the resistance of the resistor as greater currents pass through it as shown on your graph?
a) The resistance increases
b) The resistance decreases
c) The resistance stays the same
8) If either of the graphs indicate an ohmic relationship, use the graph(s) to find the resistance of the
component(s). Show your work below and include the proper units.
Extra Credit:
Using the schematic of a circuit above, answer the following. Assume that the Battery has a voltage of 12 V.
1) Find the total resistance of the circuit.
2) Find the current passing through R1.
3) Find the current passing through R6.
4) Find the voltage drop across R3.