Series, Parallel and Combinations Circuits
Course:
Name(s):
Instructor:
Date:
Section:
Introduction and Objectives:
In this experiment the circuit characteristics of resistors when connected in series, parallel or mixed
combination will be investigated. Ohm’s law is still applicable in this case.
Theory:
Resistors can be connected in Series, Parallel or mixed combination. Depending on the type of resistor
combination, the circuit might have different values of voltage and/or current across different part of
the circuit. Below we discuss types of resistor combination and the resulting circuit properties in detail:
a) Series Combination: Resistors are said to be connected in series when they are connected in a line
(head to tail) so that the current does not have any other alternate path to go through [Figure 1].
Current: Since there is no alternate path, the same current passes through all the resistors: I = I1 = I2 =
I3.
Voltage: The voltage drop across each resistor is not equal to V, but the sum of the voltage drops:
V = V1 + V2 + V3
Resistance: The equivalent resistance of the three resistors is: Req = R1 + R2 + R3
R2
R1
R3
A
V
Figure 1: Resistors in Series
b) Parallel: Resistors are said to be connected in series when all the “heads” are connected together as
are all the “tails” [Figure 2].
R1
R2
R3
V
Figure 2: Resistors in Parallel
Voltage: the voltage drops across all the resistors are the same and equal to the voltage (V) of the
source: V = V1 = V2 = V3
1
Current: the current (I) from the source gets divided among the resistors:
I = I1 + I2 + I3.
Resistance: The equivalent resistance of the resistors can be calculated by the formula:
1/Req = 1/R1 + 1/R2 + 1/R3
Equipment Required:
Three resistors (eg. 100 Ω, 150 Ω and 470 Ω), ammeter, voltmeter or multi-meter, circuit board,
connecting wires, power supply.
Lab Procedures:
Before you begin your lab, read the color codes of the three resistors and record them in Table1.
Table 1:
Resistor
Color code on resistor
(bands seen)
Magnitude of resistance
(corresponding Ω value
from color code chart)
R1
R2
R3
I) Series Circuit:
1) Connect the three resistors and the voltage source into the series circuit as shown in Figure 1 above.
Use a voltage of about 1.5 volts for your experiments.
Three resistors in series
2
2) Use the ammeter (connected into the circuit) to read the current in the circuit across each resistor.
The current should be the same throughout the circuit. Record these values in the first row of Table 2.
Figure 3: Reminder on how to connect Ammeter and Voltmeter
3) Connect a voltmeter across the individual resistors and then across the combination of resistors.
Record your values in the first row of Table 2.
4) Calculate R1, R2 and R3 using (R = V/I, Ohms = Volts/Amp). Record these values in the first row
of Table 3.
5) Calculate Req using Req = R1 + R2 + R3. Record this in row 1, column 4 of Table 3.
6) Calculate Req using the known values of the resistors using their color codes (add individual
resistances). Record this in row 1, column 5 of Table 3.
7) Record all the resistances in Ohms (Ω).
How to measure current across a resistor
Ammeter connected to
resistor
How to measure current across a resistor
Remove one end of the
resistor and connect it
to the positive terminal
of the ammeter
3
Negative lead from
ammeter goes back to
circuit
II) Parallel Circuit:
1) Connect the same three resistors into the parallel circuit as shown in Figure 2 above.
2) Set your power supply to deliver a voltage of about 1.5 volts. Read the voltage across each resistor.
This should be the same as the total voltage (from the source). Now insert the ammeter into each
resistor branch and record the current for all three branches. Also record the total current in the circuit.
3) Record your readings in the second row of Table 2.
4) Calculate all the individual resistances (R1, R2, R3) and the equivalent resistance (Req ) using your
data in Table 2 and record your results in Table 3 (in the second row of the parallel circuit).
5) Calculate the theoretical value of the equivalent resistance using your data in Table 1, for the
resistors in parallel: 1/Req = 1/R1 + 1/R2 + 1/R3. Record this value in row 2, column 5 of Table 3.
Three resistors in
parallel
III) Combination Circuit:
1) Connect the same three resistors into the series and parallel circuits (combination circuit) shown
below:
R1
R3
R2
V
Resistors in series and parallel
4
2) Set your power supply to deliver a voltage of about 1.5 volts.
3) Read and record the currents and voltages in all the branches.
4) Calculate the resistances using your measurements (R = V/I, Ohms = Volts/Amp)
5) Calculate the equivalent resistance.
Combination circuit
Data Tables:
Table 2
Circuit
Vtot
Series
Parallel
Combination
V1
V2
V3
I1
I2
I3
Table 3
Calculate the resistances using your measurements from table 1 and the formula: R = V/I. Enter your
answers in the table 3.
Circuit
R1
R2
R3
Req
(experimental) (experimental) (experimental) (experimental)
Series
Parallel
Combination
Calculations:
5
Req (theory)
Using Table 1
Show your formulas and calculations for Theoretical Equivalent Resistance:
i) Series:
ii) Parallel:
iii) Combination:
6
Questions:
1. In which circuit is the current the same in each element?
2. In which circuit are all the potential drops the same?
3. In which circuit is the total voltage the sum of all the individual voltages?
4. In which circuit is the equivalent resistance less than each individual resistance?
5. In which circuit is the equivalent resistance greater than each individual resistance?
7