Activity 23B
PS-2826
Voltage in a Parallel Circuit
Electricity: voltage, parallel circuit
Qty
1
1
1
2
Equipment and Materials
PASPORT Xplorer GLX
Voltage Probe (included with GLX)
CASTLE Kit
‘D’ Cell
Part Number
PS-2002
EM-8624A
PI-6602
Purpose
The purpose of this activity is to determine the relationship between voltage and the number of
light bulbs that are connected to a voltage source in a parallel circuit.
Background
Light bulbs in a parallel circuit are connected like steps of a
ladder. Each light bulb is connected directly to the voltage
source. If light bulbs are connected in parallel to a voltage
source, what happens to the brightness of the individual
bulbs as more bulbs are added to the “ladder”? What will
happen to the voltage across each individual bulb as more
bulbs are added to the circuit?
Fig. 1
Fi
1: Parallel
P
ll l circuit
i
it
Preview
Use a Voltage Probe to measure the voltage across a voltage source (‘D’ cells) and the voltage
across each bulb in a parallel circuit. Use the Xplorer GLX to record and display the voltage.
Compare the voltages.
Predict
1.
How would the voltages across each light bulb in a parallel circuit change as more bulbs
are added to the circuit?
2.
How would the brightness of the light bulbs in a parallel circuit change as more bulbs are
added to the circuit?
3.
If one bulb in a parallel circuit is removed, what happens to the rest of the bulbs?
Safety Precaution
•
Follow all directions for using the equipment.
Procedure
GLX Setup
1.
Plug a Voltage Probe into the voltage input port
on the left side of the Xplorer GLX
and then turn on the GLX ( ). A graph of Voltage (V) and Time (s) will open.
Physics with the Xplorer GLX
© 2006 PASCO
p. 169
Activity 23B
2.
Press
(
Voltage in a Parallel Circuit
PS-2826
to go to the Home Screen. Select Digits
) and press
to open the Digits screen.
Equipment Setup
1.
Put two D cells into the battery holder (from the
CASTLE Kit). Put a round light bulb in a lamp socket.
2.
Use a pair of alligator clip patch cords to set up a circuit
with the light bulb and voltage source.
•
Be careful to connect an alligator clip to the spring as
shown.
3.
Leave one clip disconnected until you are ready to collect data.
Fig. 2: Digits display
Record Data: One Light Bulb
1.
Connect the ends of the Voltage Probe to the lamp socket
in order to measure the voltage across the light bulb.
2.
Connect the clip to the voltage source to complete the
circuit. Observe the brightness of the bulb.
3.
Press Start (
) on the GLX to measure the signal from
the Voltage Probe.
•
The voltage appears in the digits display.
4.
Record the voltage across the light bulb in the
Data Table in the Lab Report section.
5.
Move the ends of the Voltage Probe to the
alligator clips that are connected to the
voltage source in order to measure the voltage
across the two D cells.
6.
Record the voltage across the two D cells in
the Data Table in the Lab Report section.
7.
Press
to stop data recording. Disconnect
the clip to the voltage source to open the
circuit.
Physics with the Xplorer GLX
Fig. 3: Equipment setup
Fig. 4: Record voltage across light bulb
© 2006 PASCO
p. 170
Activity 23B
Voltage in a Parallel Circuit
PS-2826
Record Data: Two Light Bulbs
1.
Connect a second light bulb in parallel with the first light bulb in the circuit.
2.
Connect the clip to the voltage source to complete the circuit. Record the apparent
brightness of the two bulbs.
3.
Connect the ends of the Voltage Probe to
the second lamp socket in order to measure
the voltage across the second light bulb.
4.
Press Start (
) on the GLX to measure
the signal from the Voltage Probe.
5.
Record the voltage across the seco:nd light
bulb in the Data Table in the Lab Report
section.
6.
Next, move the ends of the
Voltage Probe back to the first
lamp socket to measure the
voltage across the first light
bulb.
7.
Record the voltage across the
first light bulb in the Data Table.
8.
Finally, move the Voltage Probe
back to the source and measure
the voltage across the batteries.
9.
Press
circuit.
Fig. 6: Two bulb setup
Fig. 7 Record voltage
to stop data recording. Disconnect the clip to the voltage source to open the
Record Data: Three Light Bulbs
1.
Connect a third light bulb in parallel with the other two light bulbs in the circuit.
2.
Repeat the procedure to
measure the voltage across the
source and across each of the
light bulbs and record the
voltages in the Data Table in
the Lab Report.
Fig. 8: Three bulb setup
Physics with the Xplorer GLX
© 2006 PASCO
p. 171
Activity 23B
Voltage in a Parallel Circuit
PS-2826
3.
After recording the voltages, remove the light bulb from the middle lamp socket. Record
what happens to the other two light bulbs.
4.
Press
circuit.
to stop data recording. Disconnect the clip to the voltage source to open the
Analysis
Examine your recorded voltage data and answer the questions in the Lab Report.
Extension
Repeat the procedure with the resistors included in the CASTLE Kit instead of light bulbs.
Physics with the Xplorer GLX
© 2006 PASCO
p. 172
Activity 23B
Voltage in a Parallel Circuit
PS-2826
Lab Report - Activity 23B: Voltage in a Parallel Circuit
Name ________________________________ Date ___________
Predict
1.
How would the voltages across each light bulb in a parallel circuit change as more bulbs
are added to the circuit?
2.
How would the brightness of the light bulbs in a parallel circuit change as more bulbs are
added to the circuit?
3.
If one bulb in a parallel circuit is removed, what happens to the rest of the bulbs?
Data
1.
How bright were the two light bulbs in parallel compared to the first light bulb?
2.
How bright were the three light bulbs in parallel compared to the first light bulb?
3.
What happened in the three-light bulb parallel circuit when you removed the light bulb
from the middle lamp socket?
Data Table
One Light Bulb
Voltage Across Light Bulb:
Voltage Across Batteries:
Two Light Bulbs in Parallel
Voltage Across Light Bulb 1:
Voltage Across Light Bulb 2:
Voltage Across Batteries:
Physics with the Xplorer GLX
© 2006 PASCO
p. 173
Activity 23B
Voltage in a Parallel Circuit
PS-2826
Three Light Bulbs in Parallel
Voltage Across Light Bulb 1:
Voltage Across Light Bulb 2:
Voltage Across Light Bulb 3:
Voltage Across Batteries:
Questions
1.
How did the voltage across the two D cells compare to the voltage across the first light
bulb?
2.
How did the voltage across each of the two light bulbs in parallel compare to the voltage
across the D cells?
3.
What did you notice about the voltage across each light bulb and the voltage across the D
cells when three bulbs are in parallel?
4.
What can you say about the voltage in a parallel circuit?
5.
What happened to the light bulbs when you removed the middle bulb from the socket?
Why?
6.
If all the lights in a house are connected together in parallel and they are all turned on,
what would happen to the lights when you turn one of them off (or it burns out)?
Physics with the Xplorer GLX
© 2006 PASCO
p. 174