School Of Engineering Technology and Applied Science (SETAS)
Advanced Manufacturing and Automation Technology (AMAT)
EET 117 – Lab Instructions Section: __________________ Date:
Lab #8 GROUP: ___________________
Status and Signature :
Name: ______________________________
Series-Parallel Circuits
Based on Experiments in Basic Circuits
by David Buchla Name:______________________________
Objectives:
1. Use the concept of equivalent circuits to simplify series-parallel circuit analysis.
2. Compute the currents and voltages in a series-parallel combination circuit and verify your computation with
circuit measurements.
Required Instruments and Components:
Power supply
DMM (Digital Multimeter)
Breadboard
Alligator test leads (from the EET-117 lab kit)
Resistors: 1 kΩ, 4.7 kΩ, 5.6 kΩ, 10.0 kΩ (from the EET-117 lab kit)
Procedure
1. Obtain the resistors listed in Table 1. Measure each resistor and record the measured value in the
table.
A reminder of steps to measure resistance using lab DMM (a reference to the manual):
1. Connect the device under test to the instrument, as shown:
2. Select a resistance measurement function:
• Press Ω2 to select 2-wire ohms.
Table 1. Measured resistance values (use 3 significant digits, metric prefixes).
Component Listed Value Measured Value Marks
R1 1 kΩ /1
0.996k
R2 4.7 kΩ /1
4.68k
R3 5.6 kΩ /1
5.532 k
R4 10.0 kΩ /1
9.90k
Total: /4
2. Connect the circuit shown in Figure 1. Notice that the identical current is through R1, and R4 so we
know that they are in series. R2 has both ends connected directly to R 3 so these resistors are in
parallel.
Fig. 1
3. You can begin solving for the currents and voltages in the circuit by replacing resistors that are
either in series or in parallel with an equivalent resistor. In this case, begin by replacing R 2 and R3
with one equivalent resistor. Label the equivalent resistor R 23. Draw the equivalent series circuit
in the space provided below. Show the value of all components, including R23.
r12 2.56 k
Marks: / 10
4. The equivalent circuit you drew above (in step 3) is a series circuit.
To calculate currents and voltages in the original circuit you can apply the following steps:
a) Find the total current, I T, in the circuit by substituting the total voltage and the total
resistance into Ohm's law. Enter the computed total current.
b) In the equivalent series circuit, the total current is flowing through R1, R23, and R4.
c) The voltage drop across each of these resistors can be found by applying Ohm's law to each
resistor. Compute V1, V23, and V4 using this method.
d) Use V23 and Ohm's law to compute currents in R2 and R3 (I2 and I3) of the original circuit. As
a check, verify that the computed sum of I 2 and I3 is equal to the computed total current.
Compute the total resistance RT and show calculations:
Rt = R1+R23+R4= 1k+ 2.56k+ 10k= 13.56k
Compute the total current IT and show calculations:
It = Vt/ Rt = 12/13.56 = 0.885 mA
Compute voltages on different parts of this equivalent circuit (V1, V23, V4) and show calculations:
Voltage across V1= 3.65 v , V23= 0.62v , V4= 7.73 V
Compute currents I2 and I3 and show calculations:
V 2 = V3 = 0.62V, I2= V2/R2=0.62V/4.7k= 132 mA
I3= V3/R3 = 0.62V/5.6k = 111 mA
Enter calculated above results in Table 2.
5. Measure, enter, and compare values in the column beside (Measured in Table 2). Important
reminder: don’t forget to disconnect the power supply when measuring the total resistance.
When measuring current always connect the ammeter in series and select appropriate
function (DCI) with associated connections on DMM (GND & I).
Table 2. Measured and computed values (use 3 significant digits, metric prefixes).
Computed (Ohm’s Law) Measured Marks
Vs 12.0 V 12.06 V /2
RT 13.56 k 13.4 k /4
IT 0.885 mA 782mA /4
V1 884 mV 8.93 mV /4
V23 2.27 V ` 2.27 V /4
V4 8.85 V 8.87V /4
I2 I2= V2/ R2 = 0.483 ma /2
I3 I3= V3/ R3= 2.27/5.6k= 0.405 mA /2
Total: /26
6. The voltage divider rule can be applied directly to the equivalent series circuit to find the voltages
across R1, R23, and R4. Find V1, V 23, and V4 using the voltage divider rule. Tabulate the results in
Table 2 and place the results in Table 3.
Table 3. Computed values (use 3 significant digits, metric prefixes).
COMPUTED Marks
(Voltage Divider Formula: show formula and calculations)
V1 /2
V1= R1/R1+R23+ R4x Vt= 1/2.56+1+10 x 12= 0.884 V
V23 /2
V23=R23/R1+R23+ R4= 2.56/13.56 x 12V=2.27V
V4 /2
V4 = R4/ RTx Vs = 10/13.56 x 12V= 8.85 V
Total: /6
7. The current divider rule can be applied to the parallel circuit to find the current in its branches (e.g.
I2 and I3). Tabulate the results from Table 2 and place results in Table 4 showing formulas and
calculations.
Table 4. Computed values (use 3 significant digits, metric prefixes).
COMPUTED Marks
(Current Divider Formula: show formula and calculations)
I2 /2
I2= R3/R2+R3 x IT= 5.6/4.7+5.6 x 0.885
I3 /2
Total: /4
8. Change the circuit to the circuit shown in Figure 2. Draw an equivalent circuit by combining the
resistors that are in series. Enter the values of the equivalent resistors on your schematic drawing
and in Table 5.
Fig. 2
Marks: / 10
Table 5. Measured and computed values (use 3 significant digits, metric prefixes).
Computed Measured Marks
R12 5.65 /4
R34 15.4 /4
RT 5.65 /4
IT 16.1 mA /4
I12 15.5 mA /4
I34 0.557 mA /4
V1 2.66 /4
V2 0.56v /4
V3 3.15 /4
V4 5.64 /4
Total: /40
Conclusions. The conclusion summarizes the important points of the laboratory work. You must
analyze the examples to add emphasis to significant points. You must also include features and/or
things you have done /benefits of a particular procedure, instrument, component, or circuit directly
related to the experiment.
Marks: / 20
Rubric-Grading
Criteria Max. Marks
Punctuality 10
Lab Safety 20
Procedure 100
Conclusion 20
Neatness, Spelling, Grammar, and Sentence Structure 10
Total: /160
