YanbuUniversityCollege
Preparatory PHYSICAL SCIENCE (PHSC001)
Lab. Exercise No. 2
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Study Series and Parallel Circuits
Object:
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To study current flow in series and parallel circuits.
To study voltages in series and parallel circuits.
Theoretical Background:
Components in an electrical circuit are in series when they are connected one after the other, so that the
same current flows through bothof them. Components are in parallel when they are in alternate branches
of a circuit. Series and parallel circuits function differently.
You may have noticed the differences in electrical circuits you use. When using some decorative holiday
light circuits, if one lamp burnsout, the whole string of lamps goes off. These lamps are in series. When
a light bulb burns out in your house, the other lights stay on.Household wiring is normally in parallel.
The first principle to understand about series circuits is that the amount of current is the same through
any component in the circuit. This is because there is only one path for electrons to flow in a series
circuit, and because free electrons flow through conductors like marbles in a tube, the rate of flow
(marble speed) at any point in the circuit (tube) at any specific point in time must be equal.
The first principle to understand about parallel circuits is that the voltage is equal across all components
in the circuit. This is because there are only two sets of electrically common points in a parallel circuit,
and voltage measured between sets of common points must always be the same at any given time.
Equipment:
3 Lamp sockets (figure 1),3 Filament lamps, 12 V / 0.1 A(figure 1),Multi-meter (figure 2),Connection box
(figure 3),Connecting cord, l = 500 mm, blue(figure 4),Connecting cord, l = 500 mm, red (figure 4),
Power supply, 12 V (figure 5).
PHSC001, Lab-1
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WARNING!
Have your instructor approve eachcircuit before you plug in a powersupply! Be
sure the power supply isturned off before you plug it in.
Series Circuit Schematic (Figure 6)
The first type of circuit you will construct isa series circuit (Fig. 6 and Fig. 8).
Ina series circuit the resistors are connectedend-to-end such that the current is
thesame through each resistor; the currenthas only one path available. The
voltagedrop across each resistor depends on theresistor value.For a series circuit
the total equivalentresistance, Req, is:
Parallel Circuit Schematic (Figure 7)
The second type of circuit you willconstruct is a parallel circuit (Fig. 7and Fig. 9).
Resistors are said to be inparallel when they are connected at bothends, such
that the potential differenceapplied across the combination is the sameas the
potential difference applied acrossan individual resistor. The current througheach
resistor depends on the resistor value.The current has more than one
pathavailable, and takes all available paths.For a parallel circuit the total
equivalentresistance, Req, is:
PHSC001, Lab-1
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Procedure:
Series Circuit
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Construct a series circuit (Fig. 6) with the power supply (unplugged
from outlet) and twolamp sockets with filament lamps as shown in the
figure 8.Connected in the appropriate places.Use connection box (Fig.
3) (Note: There are more than one way to do this).
Select the voltmeter function of multimeter (Fig. 2); connect it to your
circuit so that it will measure the potential difference. When a current
is flowing. Select the ammeter function (Fig. 2) on the multimeter;
insert it into your circuit.
Get instructor approval of yourcircuit!
Plug in the power supply. Adjust the power supply until the potential difference across the filament lamp
(Fig. 1) is 2.0V; this is the same as the potential difference across the power supply.
Record the current (A) and the voltage (V). Repeat this process in 1.0V increments up to 4.0V.
With the voltage across the power supply set at 4.0V, disconnect the voltmeter. Maintaining the same
orientation of the leads, measure the potential difference across each resistor.
Add these potential differences. Does equal 4.0V?
Turn off, and then disconnect, the powersupply from the circuit. Measure andrecord the resistance of the
circuit, Req,(Fig. 8) with theohmmeter function of the multimeter.
Observations:
Voltage supplied V=_____________ volts
Current through the circuit I=___________ ampere
Filament
Lamp
Voltage across each
filament lamp (volts)
Current through each
filament lamp (amp)
1
V1=_______
I1=_______
2
V2=_______
I2 =_______
Result:
V1 + V2= ______ volt
Verify:
I1 = I2 = I
Verify:
V1 + V2 = V
Verified: __________ [Yes/No]
PHSC001, Lab-1
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Parallel Circuit:
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Construct a parallel circuit (Fig. 7) with the power supply
(unplugged from outlet) and twolamp socket with filament lamp,
see figure
There is variety of ways to do this.
Get instructor approval of your circuit!
Connect the multimeter to the circuit. Plug in the power supply
and increase the power until the potential difference is 2.0V.
Record the voltage and current.
Measure and record the potential difference across each resistor.
As you increase the potential difference, in 1.0V up to 4.0V, measure and record the voltage and current.
Observations:
Voltage supplied V=_____________ volt
Current through the circuit I=___________ ampere
Filament
Lamp
Voltage across each
filament lamp (volts)
Current through each
filament lamp (amp)
1
V1=_______
I1=_______
2
V2=_______
I2 =_______
Result:
I1 + I2 = _______ amp
Verify:
I1 + I2 = I
Verify:
V1 = V2= V
Verified: __________ [Yes/No]
PHSC001, Lab-1
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Review Questions
Q 1.
Why should the voltage drops (potential differences) across the resistors connected
in parallel be the same? Were your values equal?
Q 2.
Are the circuits in houses wired in series and/or parallel? What evidence do you
have for your answer?
End of the Exercise
PHSC001, Lab-1
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