Lab Report: Experiment 2 - Resistance and DC Circuits - Griffith

This lab report details an experiment on DC circuits and resistance, focusing on voltage dividers and the application of Kirchhoff's laws. The experiment involved assembling circuits with various resistors, measuring voltage and current, and analyzing the relationship between resistance and current. The report includes an introduction to voltage dividers and their limitations, a description of the experimental procedure, and a presentation of the results in tables and graphs. The analysis discusses the inverse proportionality of resistance and current, as well as the application of Kirchhoff's laws at circuit nodes. The conclusion recommends against using a potential divider in the new technology due to its tendency to reduce current to the load. The report also touches on resistor color codes and the importance of stable voltage in electronic circuits. Desklib provides this and other solved assignments for students.

INSTITUTIONAL AFFILIATION
FACULTY OR DEPARTMENT
COURSE ID & NAME
EXPERIMENT 2 LAB REPORT
TITLE: CIRCUITS
STUDENT NAME
STUDENT ID NUMBER
PROFESSOR (TUTOR)
2018

INTRODUCTION
Voltage dividers as a power supply
Many circuit systems are connected to a load which may be supplied by one or more power
sources. When many power sources are used in a given project or system, they tend to cost the
company a lot of money. The alternative method is to use the voltage divider method where one
power source is implemented and the loads are placed in parallel mode to the power source. The
optimal circuit for the new technology demonstrates the circuit schematic,
Figure 1 Optimal Circuit for the new Technology
The voltage divider is also the current divider and it uses the Kirchhoff’s voltage or current law
in determining the amount of voltage or current that is required or consumed by each load. For
instance, in the discussion section, the data recorded during the experiment is used to estimate
the amount of voltage and power consumed by each load. It is also important to note that the
main power supply unit may provide very large voltages while the load may only require less.
For instance, the gadgets chargers require about 5 volts to operate. The variable power supply
unit may be tapped to provide 12 volts. In such a case, a voltage divider is implemented to ensure
that the charger receives 5 volts and not the entire 12 volts as supplied. The voltage divider, in
turn, protects the loads by providing the right amounts of voltage. It is a voltage regulation
strategy where the voltage is dropped to a given value within the circuit and the energy
efficiency in these systems is not a major point of concern. The voltage divider theorem follows
that at a node,

V i nnode
=V ou tnode
Using ohm’s law,
V =IR
The voltage at a given load is obtained from the Thevenin of a circuit such that,
V th= R2
R1+ R2
. V ¿
In many power sources, the voltage sources have a very low internal resistance. The loads need
to be powered from current sources and the current sources are such that each load gets the
amount of current as is rated for it. The current sources, on the other hand, tend to have large
internal resistances. Most of the loads are highly dependent on the amount of voltage that flows
through them and the voltage value critically affects the voltage levels of the system. For
instance, when an LED is powered on by such a circuit, it requires that at 5 volts the LED turns
on and at lower voltage values of less than 1 volt, it turns off. Such loads require very stable
voltages to avoid giving out the wrong information. When the voltage is unstable the LED could
give the wrong information. For instance, a user may think that a shaver has low power or charge
in its system because the LED may turn on Red instead of Green.
It is important to note that all the currents flowing to a node are equal to zero. The net amount of
the current does not change but the current flowing through the different branches changes based
on the load. It is given as,
∑ I=0
∑
n =1
N
In=I1 + (−I 2 ) + (−I 3 ) + (−I4 )+ I 5=0
In this case study, the optimal circuit has a node with three branches hence,
∑
n =1
N
I n=I 1 + (−I 2 ) + (−I 3 )
I 1=I2 +I3

Resistor codes
As physicists, it is good practice to know the value of resistance of a resistor based on the color
codes. The color codes are mainly used on the carbon and film types of resistors. Unfortunately,
many of the resistors are too small to have the color codes printed legibly for users to read. Such
small resistors have the exact value stamped on the insulated coating.
Experiment Materials
 Variable power supply (5v and 12v)
 30v variable output
 Resistors and wires
 2 Digital multimeters
 Online simulator (test theories)
Experiment Procedure
(i) The team members assembled all the experiment materials prior to the start of the lab
session.
(ii) The digital multimeter was tested for calibration errors and any concerns were raised.
(iii) The team selected the 6 resistors of the value 10k, 20k, 100k, 50k, 400k, and 800k for
use in the experiment and wires for connection. The different resistors were analyzed

using the resistor color codes to determine their values before being measured by the
digital multimeter to obtain the actual value. The resistor measured and actual
readings were recorded on the results table.
(iv) The members used jumpers to connect the variable power supply to the breadboard
where the circuit was designed. After connecting all the components as shown in the
optimal circuit design to be implemented, the circuit was powered ON.
(v) The digital multimeter was used to take voltage readings across the resistors and
along the resistors to collect current readings. The reading taken were recorded in a
table for each component.
Experiment analysis
The results obtained from the lab experiment were recorded on a table as shown below,
Resistance (Ω) ΔV Current (A) Actual Ω
10k 1.58v 160.5μ 9.92k
20k 3.221v 160.6 μ 20.2k
100k 8.13v 81.8 μ 99.2k
50k 3.94v 78.8 μ 50k
400k 4.02v 9.86 μ 392k
800k 7.46v 9.86 μ 798k
From the results,

0 1 2 3 4 5 6 7
0
100
200
300
400
500
600
700
800
900
plot of actual resistance vs measured resistance
Resistance (Ω) Actual Ω
Experiment Tests
resistance (ohms)
The error between the measured and the actual resistance is within the tolerance scale of ± 5 %
0 1 2 3 4 5 6 7
0
100
200
300
400
500
600
700
800
900
Plot of Resistance and current
Resistance (Ω)
Current (A)
Experiment Trials
R/C
The plot above shows the inverse proportionality of the resistance and the current. This follows
from the Ohm’s law where,
V ∝ IR
V
R ∝ I … hence the inverse proportionality

At the node, the Kirchhoff laws apply such that in series the same current flows through all the
load but at the node the current is divided according to the load. Assuming a constant voltage at
the parallel loads, the current can be computed as,
Conclusion
In a nutshell, it is recommended that a potential divider is not implemented in the new
technology as it tends to reduce the current as it gets to the load especially if many loads are
attached to the node point hence the technology would perform poorly. The Kirchhoff’s voltage
and current laws are used interchangeably in the design of the circuit.
References
Internet sources
http://tinyurl.com/y9hvvvvd