Physics 102
Building Circuits and Using the Oscilloscope
Phuc La, Juan Guerrero
January 29, 2006
Abstract:
The purpose of this lab is to build a circuit and use an oscilloscope because it’s
necessarily for several of the later labs. Besides, a VOM is used to measure voltage and
current of the circuit and components.
Equipment:
 3 light bulbs
 wires
 battery or power supply
 digital voltmeter (VOM)
 function generator
 oscilloscope
Procedure:
Part 01: building circuits
A series circuit
1. Using the light bulb board (3 bulbs), wires and a battery build a series circuit
using all three bulbs and a battery like Picture 01.
Picture 01: A series circuit
2. With the dial of VOM set to DCV connect the black probe to A1 and the red
probe is connected to B1 to measure the voltage of the bulb. The bulb between A1
and B1 is bulb 1. Then continue with the bulb 2 and 3.
3. Then remove one wire connecting the bulbs to the battery or power supply and
replace it with the VOM probe which is set to DCA to record the current of the
circuit. The current should be the same throughout the entire circuit.
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4. Remove one bulb from the circuit and record what happens. Try this with each
bulb.
A parallel circuit
1. Using the light bulb board (3 bulbs), wires and a battery build a series circuit
using all three bulbs and a battery like picture 02.
Picture 02: Parallel circuit
2. Set the dial of VOM to DCV. Connect the black probe to A1 and the red probe to
B1 to measure the voltage of the bulb 1 between A1 and B1. Then continue with
the bulb 2 and 3.
3. Set the dial of VOM to DCA. One wire of each branch is replaced by the VOM to
measure the current flowing through each bulb.
4. When one bulb is removed, record what happens to the brightness and the voltage
across the remaining two bulbs.
A parallel and series circuit
1. Using the light bulb board (3 bulbs), wires and a battery build a series circuit
using all three bulbs and a battery like picture 03.
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Picture 03: A parallel and series circuit
2. The dial of VOM is set to DCV. The black probe is connected to A1 and the red
probe is connected to B1 to measure the voltage of the bulb between A1 and B1.
Then continue with the bulb 2 and 3.
3. Switch the dial of the VOM to DCA. Replace the wire of each branch with the
VOM to measure the current of each bulb.
4. When one bulb is removed, record what happens to the brightness and the voltage
across of the remaining two bulbs.
Part 2: Using the oscilloscope
1. Connect the function generator to the oscilloscope by connecting the red output to
red input on the oscilloscope and black out put to black input.
2. Set the frequency dial on the function generator to about 0.9, the waveform to
sine, the multiplier to X100, the amplitude to about 3 o’clock, and the offset to 0.
3. On the oscilloscope, adjust the voltage/div dial, and the time/div dial to get a
complete sinusoidal wave on the ‘scope’s screen.
4. Record the frequency and the amplitude of the wave on the scope.
Data:
Calculation:
1. In the series circuit (picture 01)
When the 6V power supply was connected to the circuit the three bulbs lit. If one
bulb was removed, the rest of the bulbs turn off. When one bulb is removed, the circuit is
interrupted or not closed. There is no current running on the circuit, so the two other
bulbs turn off.
When the three bulbs were lit each bulb had a voltage.
Bulb
01
02
03
Voltage
V
1.962
1.810
1.806
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The current running through the circuit is the same when it goes through each bulb.
The current is 0.16 A
If only two bulbs (Bulb 01 and 02) are connected in series and the same, 6V, voltage
is run through the circuit, the two bulbs light brighter. With this circuit, each bulb has a
new voltage.
Bulb
01
02
Voltage
V
3.13
2.26
2. In the parallel circuit (picture 02)
When the 6V power supply was connected to the circuit the three bulbs lit. If one
bulb is removed, the rest of the bulbs still light. Because when one bulb is removed, the
circuit remains closed, so there is still a current running in the circuit. Also, when one
bulb is removed, the remaining two bulbs are not changed. Their brightness remains the
same because the voltage across them is not changed.
The circuit is a parallel circuit, so the voltage is the same in each component. Only,
the current is changed. It means each light has different current.
Bulb
01
02
03
Current
A
0.29
0.29
0.29
3. A Parallel and series circuit
When the 6V power source was connected to the circuit the three bulbs lit. Different
things happen when a single bulb is removed from the circuit. It depends on which bulb
is removed.
If bulb 01 is removed, the remaining bulbs still light because bulb 01 is parallel with
bulb 02 and bulb 03. Therefore when the bulb 01 is removed, the current still runs
through bulbs 02 and 03. The brightness of the remaining two bulbs is not changed.
If bulb 02 is removed, bulb 01 still lights because bulb 01 is parallel with bulb 02 and
03. Bulb 03 does not remain lit because the bulb03 is in series with bulb 02. The
brightness of the bulb 01 does not change when the other two lights go out.
If bulb 03 is removed, the bulb 01 still lights because bulb 01 is parallel with bulb 02
and 03. Bulb 02 does not light for the same reason that bulb 03 did not light previously,
which is because bulb 02 is in series with bulb 03. The brightness of the bulb 01 does not
change.
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4. Using Oscilloscope
The function generator is connected to the oscilloscope, red to red, black to black. It’s
a parallel connection because the connection uses two wires. One, red, is positive and
one, black, is negative. If the connection would be a series connection, it would be
connected positive to negative. So the connection is a parallel connection.
The period of a sine wave is 5.2 divisions from the center of the scope screen.
Besides, the time/div dial is set to 0.2 ms/div. The period of a sine wave is:
T = 5.2 div * 2 ms/div = 10 ms = 0.010 s
The frequency of the wave is the inverse of the period of a sine wave.
1
1
f  
 100 Hz 1.0 x 10 2 Hz
T 0.010 s
If the function generator was connected to a speaker, we could hear the sound
because the human ear can hear the sound frequencies between 20 Hz to 20,000 Hz.
From the scope’s screen, one was able to see the height of the wave from the
horizontal line is 2 div. Because, the voltage/div dial was set to 0.5 V/div. So the
magnitude is:
Vmax = 2 div * 0.5 V/div = 1.0 V
When the experiment was finished we were able to move the frequency dial on the
function generator and we came to the conclusion that when the frequency on the
Function Generator increases, the period of the wave decreases. The same is true vice
versa, when the frequency on the Function Generator decrease, the period of the wave
increases.
Error analysis:
There are some variations in the data. These variations have come from several sources:
 Reading errors
 Device variation
 Instructions
Reading error is a common error. In the experiment, the data is read from old worn-out
equipment. The device shows a variant number. The recorded data is at a temporary time.
Device used in the experiment also contributed to errors. Each device has a deviation, so
it adds to the affects of the result of the experiment. In the experiment, there are resistors
in devices, so the result is different from the theory result. Also the equipment is not the
highest quality. There is a voltage drop due to the quality of the connectors and the wires
in the Part 01. Also the oscilloscopes and function generators used in Part 02 are old and
no longer properly calibrated.
Not following instructions can also affect the data in the experiment. If an experiment is
done incorrectly then the data may come out incorrect. With incorrect data, a person’s
conclusion will be incorrect.
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Questions:
1. The circuits in our cars are mostly connected in parallel circuits. When one
component of the circuits is broken, the remaining components still are working.
So it doesn’t affect to the car so much. This is so the car can continue to function
properly even though something is broken in it. The broken component can be
repaired after that. Some circuits in cars are hooked up in series though, such as
car stereo systems.
2. There are many possible ways to build a single circuit that has two series branches
and two parallel branches. There are three possibilities that are illustrated below:
Method 1:
Method 2:
Method 3
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3. The three schematic diagrams are identified as follows:
Circuit A is a combination of parallel and series. The schematic of circuit A is like
picture 3.
Circuit B is a parallel circuit. The schematic of circuit B is like picture 2.
Circuit C is series circuit. The schematic of circuit C is like picture 1.
Conclusion:
In the series circuit, the current is constant. Total voltages of all components should
roughly equal the voltage of the power supply. In the parallel circuit, the voltage is
constant. Total currents that go through the components should be equal to the initial
current. The brightness of the light depends on the voltage it is receiving the type of light
it is. The scope is useful to measure the period and the amplitude of a sine wave.
Grade 85/100
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