Download 68 Voltage and Current in Simple Circuits (Voltage Sensor, Current

68
Voltage and Current in Simple Circuits
(Voltage Sensor, Current Sensor)
E&M: Voltage and current
DataStudio file: 68 Simple Circuits.ds
Equipment List
Qty
1
1
1
1
2
Items
PASCO interface (for two sensors) (see note)
Voltage Sensor( see note)
Current Sensor (see note)
AC/DC Electronics Lab
“D” cell 1.5 volt
Part Numbers
CI-6503
CI-6556
EM-8656
Note: You will not use the PASCO interface, the voltage sensor or the current
sensor for this lab; instead you will use the ammeter to measure current and
voltmeter to measure voltages. Please remember that the current you are dealing
with are the order of 1-2 A, so be sure to select the proper range to measure the
current with the ammeter or else you will damage the device.
Introduction
The purpose of this activity is to explore what happens to the voltage and the current in a simple
circuit composed of batteries and light bulbs arranged in series and then arranged in parallel. Use
a voltage sensor, a current sensor, and the DataStudio software to measure the voltage across
parts of the series and parallel circuits and a current sensor to measure the current through the
circuits.
Background
Voltage is the ratio of electric potential energy to charge. One volt is one joule of energy per one
coulomb of charge. Current is the volume of electric charge, or the
number of charges per second moving past a point in an electric
circuit. The unit for current is the ampere and one ampere is one
coulomb of charge per second. In a simple circuit of a battery
connected to a light bulb, the battery is a voltage source, and the light
bulb is a ‘load’.
Light bulbs in a series circuit are connected end-to-end like links in a
chain bracelet. Imagine a circuit with one light bulb in it. What would
happen to the brightness of the light bulb if a second light bulb were
added in series to the first light bulb? What would happen to the voltage across each individual
bulb as more and more bulbs are added in series to the circuit? What would happen to the current
through the circuit as more and more bulbs are added in series to the circuit?
Light bulbs in a parallel circuit are connected side-by-side like rung in
a stepladder. Again imagine a circuit with one light in it. What would
happen to the brightness of the light bulb if a second light bulb were
added in parallel to the first light bulb? What would happen to the
voltage across each individual bulb as more bulbs are added in parallel
to the circuit? What would happen to the current through the circuit as more and more bulbs are
added in parallel to the circuit?
PASCO
© 2004
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Physics Experiment Manual
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Prediction
1.
If one bulb in a series circuit is removed, what happens to the rest of the bulbs?
2.
If one bulb in a parallel circuit of many bulbs is removed, what happens to the rest of the
bulbs?
SAFETY REMINDER
•
Follow directions for using the equipment.
Setup
1.
Set up the PASCO interface and computer and start DataStudio. Connect the Voltage
Sensor and the Current Sensor into the interface.
2.
Open the DataStudio file: 68 Simple Circuits.ds
•
The file opens with Digits displays of voltage and current. The voltage Digits display will
show the voltage across whatever part of the circuit you select. The current Digits display
will show the current through the circuit.
3.
Insert two ‘D’ cell batteries into the AC/DC Electronics Laboratory board.
4.
Use wire leads to build up a
circuit with the two D cells,
the pushbutton switch, the
Current Sensor, and bulb
“A” as shown.
5.
Clip the leads of the Voltage
Sensor to the positive and
negative terminals of the
battery holders as shown.
Bulb “A”
Note: The diagram is not to scale
and doesn’t show the connections
to the PASCO interface.
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Pushbutton
switch
© 2004
PASCO
012-09286
Physics Experiment Manual
68 Voltage and Current
Procedure 1
Measure voltage and current for bulbs in series
Note: Data recording is easier if one person runs the computer and records data, a second person
presses the pushbutton switch, and a third person handles the Voltage Sensor leads.
One Bulb
1.
Begin measuring data. Select
‘Monitor’ from the Experiment menu
in DataStudio.
2.
Press and hold the pushbutton switch.
Observe bulb “A” and the Digits
displays of Voltage and Current.
3.
Record the values of voltage across
the voltage source (D cells) and
current through the circuit in the Lab
Report section.
4.
Move the Voltage Sensor leads to the
spring clips on either side of bulb “A” and record the voltage across the light bulb.
5.
Release the pushbutton switch.
Two Bulbs in Series
6.
Change the circuit to add bulb “B” in
series. Move the wire lead from the
negative terminal of the battery holder to
the spring clip below bulb “B”. Add a
wire lead from the spring clip below bulb
“A” to the spring clip above bulb “B” as
shown.
7.
Press and hold the pushbutton switch.
8.
Record the values of voltage across the
voltage source (D cells) and current
through the circuit with two bulbs in series.
9.
Move the Voltage Sensor leads to the spring clips on
either side of bulb “A” and record the voltage across
bulb “A” as before.
10.
Move the Voltage Sensor leads to the spring clips on
either side of bulb “B” and record the voltage across
bulb “B”.
11.
Move the sensor leads so one is on the clip above bulb
“A” and the other is on the clip below bulb “B” and
record the voltage across both bulbs.
12.
Release the pushbutton switch.
PASCO
© 2004
Add a
lead.
Move a
lead.
Measure
across 2
bulbs.
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Three Bulbs in Series
13.
Change the circuit to add bulb “C” in series. Move the
wire lead from the negative terminal of the battery
holder to the spring clip below bulb “C”. Add a wire
lead from the spring clip below bulb “B” to the spring
clip above bulb “C” as shown.
14.
Press and hold the pushbutton switch.
15.
Record the values of voltage across the voltage source
(D cells) and current through the circuit with three bulbs
in series.
16.
Move the Voltage Sensor leads to the spring clips on
either side of bulb “A” and record the voltage across
bulb “A” as before. Move the leads and measure the
voltage across bulb “B”. Move the leads and measure
the voltage across bulb “C”.
17.
Next, move the sensor leads so one is on the spring
clip above bulb “A” and the other is on the spring clip
below bulb “C” and record the voltage across three
bulbs.
Add a
lead.
Move
a lead.
Measure
across 3
bulbs.
18.
Finally, unscrew any one of the three bulbs and record what happens to the other two
bulbs. Screw the bulb back into its socket.
19.
Release the pushbutton switch.
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© 2004
PASCO
012-09286
Physics Experiment Manual
68 Voltage and Current
Procedure 2
Measure voltage and current for bulbs in parallel
Two Bulbs in Parallel
1.
Return the AC/DC Electronics Laboratory
board to the way it was at the beginning
of Procedure 1.
•
The measurements of voltage and current
for one bulb in parallel are the same as
the measurements for one bulb in series.
2.
Change the circuit to add bulb “B” in
parallel to bulb “A”. Add a wire lead from
the spring clip above bulb “A” to the
spring clip above bulb “B” as shown. Add
a second wire lead from the spring clip
below bulb “A” to the spring clip below bulb “B”.
3.
Press and hold the pushbutton switch.
4.
Record the values of voltage across the voltage
source (D cells) and current through the circuit
with two bulbs in parallel.
5.
Move the Voltage Sensor leads to the spring
clips on either side of bulb “B” and record the
voltage across bulb “B” as before.
6.
Release the pushbutton switch.
Add a
lead.
Measure
across “B”.
Three Bulbs in Parallel
7.
Change the circuit to add bulb “C” in parallel
to the other bulbs. Add a wire lead from the spring clip above bulb “B” to the spring clip
above bulb “C”. Add a second wire lead from the spring clip below bulb “B” to the spring
clip below bulb “C”.
8.
Press and hold the pushbutton switch.
9.
Record the values of voltage across the
voltage source (D cells) and current through
the circuit with three bulbs in parallel.
Measure
across “C”.
10.
Move the Voltage Sensor leads to the spring
clips on either side of bulb “B” and record the
voltage across bulb “B” as before. Move the
leads to the spring clips on either side of bulb
“C” and record the voltage across bulb “C”.
11.
Finally, unscrew any one of the three bulbs and record what happens to the other two
bulbs. Screw the bulb back into its socket.
12.
Release the pushbutton switch. Click ‘Stop’ in DataStudio.
PASCO
© 2004
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68 Voltage and Current
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Lab Report: Voltage and Current in Simple Circuits
Prediction
1.
If one bulb in a series circuit of many bulbs is removed, what happens to the rest of the
bulbs?
2.
If one bulb in a parallel circuit of many bulbs is removed, what happens to the rest of the
bulbs?
Data
Procedure 1: Voltage and Current for
Bulbs in Series
One Bulb
Item
Value
Voltage across voltage source
V
Current through circuit:
A
Voltage across bulb “A”
V
Two Bulbs in Series
Item
Procedure 2: Voltage and Current for
Bulbs in Parallel
Two Bulbs in Parallel
Value
Item
Value
Voltage across voltage source
V
Voltage across voltage source
V
Current through circuit:
A
Current through circuit:
A
Voltage across bulb “A”
V
Voltage across bulb “A”
V
Voltage across bulb “B”
V
Voltage across bulb “B”
V
Voltage across A and B
V
Voltage across A and B
V
Three Bulbs in Series
Item
Three Bulbs in Parallel
Value
Item
Value
Voltage across voltage source
V
Voltage across voltage source
V
Current through circuit:
A
Current through circuit:
A
Voltage across bulb “A”
V
Voltage across bulb “A”
V
Voltage across bulb “B”
V
Voltage across bulb “B”
V
Voltage across bulb “C”
V
Voltage across bulb “C”
V
Voltage across A to C
V
Voltage across A to C
V
What happens in the series circuit of three bulbs if one bulb is removed?
_____________________________________________________________________________
What happens in the parallel circuit of three bulbs if one bulb is removed?
_____________________________________________________________________________
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© 2004
PASCO
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Physics Experiment Manual
68 Voltage and Current
Analysis
Questions
1.
What happens to the voltage across the voltage source change as more light bulbs are
added in a series circuit?
2.
How did your calculated (theoretical) value for current through the resistors in series
compare to the actual (measured) value for current?
3.
What happens to the current through a series circuit change as more light bulbs are added
in series?
4.
How did your calculated (theoretical) value for current through the resistors compare to the
actual (measured) value for current?
5.
What happens to the voltage across the voltage source change as more light bulbs are
added in a parallel circuit?
6.
What happens to the voltages across the light bulbs in a parallel circuit change as more
light bulbs are added to the circuit?
7.
What happens to the current through a parallel circuit change as more light bulbs are added
in parallel?
8.
What happens to the brightness of each bulb in a parallel circuit as more bulbs are added?
PASCO
© 2004
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