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DC-AC Intro Q3 2007 - Laboratory Experiments (Lab 2)
CAMOSUN COLLEGE
ELECTRONICS DEPARTMENT
DC / AC Introduction - LAB 2
Resistive Series Circuit and Voltage Divider
PART A – SERIES CIRCUITS
OBJECTIVE:
1.
2.
3.
To construct some simple series circuits from a circuit diagram
To become familiar with an Ammeter and a Voltmeter.
To make measurements of current and voltage in a series circuit.
BACKGROUND
In order for an electronic circuit to function a current must flow through the circuit. A current is the
measure of the rate of change of charge flowing past a certain point in the circuit. Current is
measured by an ammeter placed in series with the circuit, which then displays the result in Amperes.
The movement of electrons in the circuit induces current, since electrons are the charge carriers.
In order for the current to flow in the circuit there must be a potential difference across the
components in the circuit. This potential difference is measured by using a voltmeter which
measures the voltage between any two points in the circuit. This potential difference is measured in
units of Volts. Note that this reading will have a polarity associated with it, the voltage may be
either positive or negative, depending on the reference point chosen.
A voltmeter is therefore connected across a component, or circuit, and measures the voltage or
“voltage drop” across the component. Note: at this point in our course we will consider test
equipment such as voltmeters or ammeters as “ideal components” which do not introduce any
resistance or have an effect on the circuit in any way. This is called loading effect.
In order to measure the current flowing in the circuit, an ammeter must be connected in the path of
the electrons. To make a measurement in a circuit the circuit must therefore be broken at the point
in which the current is to be measured and the meter inserted between the two parts of the circuit.
The red terminal or the terminal marked with a (+) must be connected towards the side of the circuit
connected to the red terminal or positive (+) marking of the supply. Polarity MUST be observed!
We will be building some simple electrical circuits using resistors. As their name might suggest to
you, they resist the flow of current in the circuit. There are many different types of resistors and they
are manufactured with a wide range of values, as you have already discovered in a previous lab.
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DC-AC Intro Q3 2007 - Laboratory Experiments (Lab 2)
Your Lab instructor will explain how to read the circuit symbols we will be using in this lab and
will also explain how to connect the circuit using the test equipment on your bench.
Remember, labs are an important part of the learning environment so feel free to ask questions.
PROCEDURE
Before building the circuits first connect the voltmeter to the power supply terminals
(+ to + and – to -) and adjust the supply until 10 Volts is indicated. Switch off the supply and
disconnect the voltmeter without adjusting the voltage control knob. Now you are ready to build the
first circuit.
For the following circuits connect up the ammeter and voltmeter in the positions shown using
appropriate ranges where applicable. If only a single meter is available measure V then I.
Note: When you have finished connecting up each circuit, get your instructor to check your work
before switching on the supply. Recheck that the supply is as close to 10 V as possible and then
record the current and voltages for each circuit and check against the given expected values.
Figure 2
Figure 1
+
mA
-
+
+
Vs
R1
10 V
1k
V
Vs
10 V
mA
+
R1
1k
V
-
-
+
R2
1k
Instructor’s Initials: ______________
V
-
Make note of all the actual values for current, resistance and voltage on the circuit diagrams
above. Note that this should be done for ALL labs during this course even if not specifically
asked for. By following this simple procedure you will ensure that circuit components and
voltages are correct. There is also less chance of making an error in the construction of the circuit if
the schematic diagram is followed closely and in a logical order. Build your circuit so that it
resembles the diagram provided. This will make troubleshooting easier. Always verify the basic
circuit parameters.
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DC-AC Intro Q3 2007 - Laboratory Experiments (Lab 2)
PART B – Voltage Dividers
OBJECTIVE:

To verify the operation of fixed unloaded voltage dividers.

To be able to predict the operation of variable voltage dividers.
PROCEDURE:
1.
Connect the following circuit. Measure the voltage drop across each resistor and the total
current and record this data in Table A, on the following page. Compare the measured
values with the calculated values. Remember to check all resistor values on the DMM or
bridge first. Use only the measured values for all calculations. Point C is the reference:
Figure 3 Basic Series Circuit
A
Measured Values
B
Vs = _________ V
R2
R1 = _________
R1 1 k
4k7
+
C
Vs
2k2
12 V
-
D
-
2.
3k3
A
R2 = _________k
R3 = _________k
R4
+
E
R4 = _________k
If point C remains our reference point, i.e., 0 Volts, measure voltage drops and determine the
voltage difference between points VB and VE.
VB = ___________
1.
R3
VE = ___________
VBE = ___________
Confirm Ohm’s Law by measuring the circuit current and total circuit resistance. Explain
any discrepancies between the calculated and measured values. Compare to Vs as well.
______________________________________________________________________________________________
______________________________________________________________________________________________
______________________________________________________________________________________________
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DC-AC Intro Q3 2007 - Laboratory Experiments (Lab 2)
RESULTS for Figure 3, on the preceding page:
Table A
MEASUREMENT
CALCULATED
MEASURED
VAB
VBC
VCD
VDE
VA
VC
VD
ITOTAL
2.
Connect the following circuits depicted in Figures 4 and 5. Measure the range of output
voltage between X and Y for each circuit. Record this data in Table B, on the following
page. Compare the measured with calculated values and explain any discrepancies.
_________________________________________________________________________
R1
Vs
+
10 V
-
10 k
R1
X
X
10 V
-
Y
10 k
+
R2
2k2
Y
Figure 4
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DC-AC Intro Q3 2007 - Laboratory Experiments (Lab 2)
Figure 6
2k2
+
Vs
- 20 V
R1
R2
X
10 k
1k
R3
Y
Table B - RESULTS for Figures 4, 5 and 6:
Circuit
Calculated range of voltage XY
Measured range of voltage XY
Figure 4
Figure 5
Figure 6
3.
Referring to Figure 6, redesign the circuit and calculate new values for the upper and lower
resistors (R1 and R3) to obtain a VXY voltage range of 5 to 10 Volts. The potentiometer, R2
remains unchanged at a value of 10k.
4.
If an ammeter had been connected in series with the power supply to the circuit of Figure 6,
would the total current have altered as the potentiometer was varied? Explain your
reasoning.
5.
What happens to the circuit current of Figure 6, if the potentiometer is connected as a
rheostat (i.e. the wiper is connected to one of the two outside terminals, or one cut off)?
What are the minimum and maximum values of circuit current using this configuration?
(Continue…)
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