Experiment 16: Series and Parallel
Circuits
Figure 16.1: Series Circuit
Figure 16.2: Parallel Circuit
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Experiment 16: Series and Parallel Circuits
Figure 16.3: Combination Circuit
EQUIPMENT
Universal Circuit Board
(2) 100-⌦ Resistors
(2) 200-⌦ Resistors
(2) 300-⌦ Resistors
(2) Digital Multi-Meters
Power Supply
(5) Jumpers
(6) Wire Leads
Experiment 16: Series and Parallel Circuits
Advance Reading
87
resistor value. The current has more than one path
available and takes all available paths.
Text: Resistors in series, parallel, combination.
For a parallel circuit, the total equivalent resistance,
Req , is:
Lab Manual:
Appendix B
Appendix C - DMM
N
Objective
The objective of this lab is to study circuits with resistors connected in series, parallel, and combination and
to determine the internal resistance of an ammeter.
X 1
1
1
1
1
1
=
+
+
+ ··· +
=
(16.2)
Req
R1
R2
R3
RN
Ri
i=1
(Resistors in Parallel)
Theory
In the previous experiment, you constructed 4 circuits,
each circuit built with one resistive element. In this
experiment, you will construct circuits using multiple
resistors.
The first type of circuit you will construct is a series
circuit (Fig. 16.1 and Fig. 16.4). In a series circuit,
the resistors are connected end-to-end such that the
current is the same through each resistor: The current
has only one path available. The voltage drop across
each resistor depends on the resistor value.
For a series circuit, the total equivalent resistance,
Req is:
Req = R1 + R2 + R3 + · · · + RN =
(Resistors in Series)
N
X
Ri
(16.1)
i=1
Figure 16.4: Series Circuit Schematic
The second type of circuit you will construct is a parallel circuit (Fig. 16.2 and Fig. 16.5). Resistors are
said to be in parallel when they are connected to each
other at each end. In this way, the potential di↵erence applied across the combination is the same as the
potential di↵erence applied across an individual resistor. The current through each resistor depends on the
Figure 16.5: Parallel Circuit Schematic
The third type of circuit you will construct is a combination circuit (Fig. 16.3 and Fig. 16.6). Resistive
elements are not connected in series or parallel. To
calculate the total equivalent resistance of a combination circuit, it should first be simplified (reduced to an
equivalent resistor, Req ). This is done by choosing resistors that are connected in either series or parallel,
one step at a time, adding those elements by use of
Eq. 16.1 or Eq. 16.2, then proceeding to the next set
of elements.
Figure 16.6: Combination Circuit Schematic
Note that it is not correct to, for example, calculate
the resistance of the 3 resistors across the top of the
circuit using Eq. 16.1, and then calculate the resistance
of R4 , R5 , and R6 using Eq. 16.2. You must identify
which resistors are either in parallel or in series, then
apply the appropriate equation one step at a time.
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Prelab 16: Series and Parallel Circuits
Name:
1. What is a series circuit? (10 pts)
2. What is a parallel circuit? (10 pts)
3. Is the equivalent resistance, Req , of a series circuit greater than or less than any individual resistor? (10 pts)
4. Is the equivalent resistance, Req , of a parallel circuit greater than or less than any individual resistor? (10 pts)
5. Calculate Req for each of the first three circuits shown in Fig. 16.4 - Fig. 16.6 using the stated nominal values
for resistance. (Show all work on back of this sheet.) (25 pts)
6. You will plot I vs. V for each of the three circuits on one graph. What value should each slope have (use the
stated values for resistance)? (25 pts)
7. Create Data Tables in your lab notebook for all parts of this experiment. Sketch the column headings on the
back of this sheet. (10 pts)
Experiment 16: Series and Parallel Circuits
PROCEDURE
PART 1: Series Circuit
Record all data in table format.
Recall that (i = 1, 2, . . . , n)
1. Measure Ri , then construct a series circuit
(Fig. 16.4) with 100-⌦, 200-⌦, and 300-⌦ resistors
and ammeter (200 mA DCA); do not connect the
power supply yet.
2. Draw the schematic using measured Ri ’s.
3. Calculate Req .
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PART 3: Parallel Circuit
16. Repeat Part 1, Step 1 - Step 8, for the parallel circuit (Fig. 16.5).
17. Does V2 = V1 + VA , or does V2 = V1 = V3 ? Are
each of these values negative or positive?! Yes, it
matters!
18. Does V = |V1 + VA |?
PART 4: Combination Circuit
19. Repeat Part 1, Step 1 - Step 8, for the combination
circuit (Fig. 16.6).
4. Measure Req .
5. Connect the unplugged power supply and the voltmeter (DCV) to your circuit.
Get instructor approval of your circuit
6. Always be sure the power supply is turned o↵ before you plug it into an outlet. Plug in the power
supply, and set the voltage to 1.00 V. Measure the
current and voltage.
7. Record the current (A) and the voltage (V) as you
increase the voltage in 1.0 V increments up to 4.0 V.
8. Leave the voltage at 4.0 V; disconnect the voltmeter
from the power supply. Maintaining the same orientation of the leads (if clockwise, black follows red),
measure Vi .
P
9. Add these potential di↵erences ( i=1 Vi ).
P
10. Does i=1 Vi equal 4.0 V? If not, ask your TA for
guidance.
PART 2: Internal Resistance of an Ammeter
PART 5: Graphing
20. Graph I vs. V for each of the first three circuits on
one graph (Part 1, Part 3, and Part 4).
21. Part 5 of this experiment may also be on an exam.
Be certain you know how to produce a complete
graph. Ask for help if needed.
QUESTIONS
1. Why should the voltage drops (electric potential differences) across the resistors connected in parallel
be the same? Were your values equal?
2. Calculate the equivalent resistance of each of the
first three circuits you constructed for this experiment using your measured values. Show each step
in this process (math and schematic). Remember
to include RA in your calculations.
3. Consider your data from Part 2. Create a table similar to the one shown below. Why does Req change
when you change the scale of the ammeter?
11. Turn o↵, then unplug and disconnect the power supply and the ammeter from the circuit. (Note that
you will need to insert a jumper when the ammeter
is disconnected in order to complete the circuit.)
Ammeter Scale
12. Measure Req of the circuit.
20 µA
13. Insert the ammeter (scale: 200 µA DCA) in the
circuit.
200 µA
14. Measure Req .
15. As you change the scale of the ammeter, measure
Req for each of the ammeter scales (e.g., 2 mA,
20 mA). You will have a total of 8 Req ’s.
No Ammeter
2 mA
20 mA
200 mA
2A
20 A
Req
RA