Lab Activity
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18 Voltage in a Series Circuit
Purpose
Explore the relationship between voltage and the number of light bulbs that are
connected to a voltage source in a series circuit.
Background
Detailed information and formulas necessary for the students to have a clear
understanding of the activity.
Materials
Equipment
• PASPORT Xplorer GLX
• CASTLE Kit
• Voltage Probe (included
with GLX)
• 'D' Cell, 2
Safety Precautions
•
Follow the directions for proper use of the equipment.
Pre-Lab Questions
1) How will the voltages in a series circuit change as more light bulbs are added to the
circuit?
2) How will the voltage across the voltage source compare to the voltage across the
light bulbs in a series circuit?
Procedure
Use a Voltage Probe to measure the voltage across a voltage source ('D' cells) and the
voltage across each bulb in a series circuit. Use the Xplorer GLX to record the voltage.
Compare the voltages.
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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.
3) Be careful to connect an alligator clip to the
spring at the end of one D cell as shown.
Fig. 1 Equipment setup
4) Leave one clip disconnected until you are ready to collect data.
Xplorer GLX Setup
1) Plug a Voltage Probe into the voltage input port (v) on the left side of the Xplorer
GLX and then turn on the GLX (p).
A graph of Voltage (V) and Time (s) will open.
2) Press h, r, c to open the 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 s on the GLX to measure the signal from
the Voltage Probe.
Fig. 2 Record voltage
across light bulb
The voltage appears in the digits display.
4) Record the voltage across the light bulb in the Data Table in your Lab Report.
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 your Lab Report.
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Fig. 3: Record voltage across
D cells
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7) Press s to stop data recording. Disconnect the clip to the voltage source to open
the circuit.
Record Data: Two Light Bulbs
1) Connect a second light bulb in series 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.
Fig. 4: Two bulb setup
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 s on the GLX to measure the signal
from the Voltage Probe.
The voltage appears in the digits display.
Fig. 5: Record voltage
5) Record the voltage across the second light bulb
in the Data Table in your Lab Report.
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 in your Lab Report.
8) Press s to stop data recording. Disconnect the clip to the voltage source to open
the circuit.
Record Data: Three Light Bulbs
1) Connect a third light bulb in series with the other
two light bulbs in the circuit.
2) Repeat the procedure to measure the voltage
across each of the light bulbs and record the
voltages in the Data Table in your Lab Report.
Fig. 8: Three bulb setup
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 s to stop data recording. Disconnect the clip to the voltage source to open
the circuit.
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Analyze
Data Table
)One Light Bulb
Voltage Across Light Bulb:
Voltage Across Batteries:
)Two Light Bulbs
Voltage Across Light Bulb 1:
Voltage Across Light Bulb 2:
Sum of the Voltages Across Both Bulbs:
)Three Light Bulbs
Voltage Across Light Bulb 1:
Voltage Across Light Bulb 2:
Voltage Across Light Bulb 3:
Sum of the Voltages Across Three Bulbs:
Analysis and Synthesis Questions
Examine your recorded voltage data and answer the folllowing questions in your Lab
Report
1) How bright were the two light bulbs in series compared to the first light bulb?
2) How bright were the three light bulbs in series compared to the first light bulb?
3) What happened in the three-light bulb circuit when you removed the light bulb from
the middle lamp socket?
4) How did the voltage across the two D cells compare to the voltage across the first
light bulb?
5) How did the voltage across the two light bulbs in series compare to the voltage
across one light bulb? How did the sum of the voltages across two bulbs compare
to the voltage across the D cells?
6) What did you notice about the voltage across each light bulb and the total voltage
across all three light bulbs in the third part of the procedure?
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7) What can you say about the voltage in a series circuit?
8) What happened to the light bulbs when you removed the middle bulb from the
socket? Why?
9) If all the lights in a house are connected together in series and they are all turned
on, what would happen to the lights when you turn one of them off (or it burns out)?
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