INSTITUTO POLITÉCNICO NACIONAL

ESCUELA SUPERIOR DE COMPUTO

LABORATORY OF
ELECTRICAL CIRCUITS

"Practice 2 OHM'S LAW"

Group:3CM2

Team: 1

Members:

Aguilar Olguin Luis Felipe

Barranco Garcia Kevin Alexis

Bazán Tehuitzil Oscar Damián

Gerardo Arroyo Rodríguez (LISTENER)

Profesor: Edmundo René Durán Camarillo

Date of completion: 17 de septiembre de 2024

Delivery date: 24 de septiembre de 2024

Página 1
 INDEX
I. Theoretical Framework…………………………………. 3

a) Voltage dependence …………………………………….. 5

b) Dependence on resistance…………………………………. 9
c) Calculation of the power in the resistors.………………….. 12
II. Questionnaire …………………………………… 13
III.- Conclusions………………………………………… 14
IV.- Bibliography………………………………………… 14
V.-Annexes…………………………………………………15

Página 2
Theoretical Framework

Ohm's Law is one of the fundamental principles of electricity, established by the

German physicist Georg Simon Ohm in 1827. This law describes the relationship
between electric voltage, current, and resistance in an electric circuit. Its significance
in the theory and practice of electrical engineering, electronics, and physics is
crucial, as it provides the foundation for understanding and designing electrical
systems.

To understand Ohm's Law, it is essential to define certain basic concepts. Electric

Current (I) is the flow of electrons through a conductor and is measured in amperes
(A). It is generated due to the potential difference between two points, which causes
the movement of electric charges. Electric Voltage (V), or potential difference, is the
electrical potential between two points in a conductor. It represents the "force" that
drives electrons to move through the circuit and is measured in volts (V). Electrical
Resistance (R) is the opposition a material presents to the flow of current.
Resistance depends on the type of material, the length, and the cross-sectional area
of the conductor. It is measured in ohms (Ω).

Ohm's Law states that the current flowing through a conductor between two points
is directly proportional to the voltage applied between those two points and inversely
proportional to the resistance of the conductor. This is expressed by the formula:

V=I*R

Where V is the voltage in volts (V), III is the current in amperes (A), and RRR is the
resistance in ohms (Ω). This statement implies that for a given resistance, the higher
the applied voltage, the greater the current flowing through the circuit. Similarly, if
the resistance increases while the voltage remains constant, the current will
decrease.

In electric circuits, Ohm's Law is fundamental for analysis and design. Depending on
the type of circuit, the relationship between voltage, current, and resistance can be
evaluated in different ways. In direct current (DC) circuits, the current flows in one
direction. A classic example is a battery connected to a resistor. Using Ohm's Law,
the current flowing through the circuit can be calculated if the voltage from the source
and the resistance of the component are known:

𝑣
𝐼=
𝑅
This formula is useful for determining the current consumption in various electrical
devices, such as light bulbs or motors.

Página 3
In series circuits, the current is the same through all components, but the total
voltage is the sum of the voltages across each component. The total resistance of
the circuit is the sum of the individual resistances:

𝑅𝑇 = 𝑅1 + 𝐵2 + 𝑅3 + ⋯ + 𝑅𝑛
By applying Ohm's Law, it is possible to calculate the voltage and current at any
point in the circuit. In parallel circuits, the voltage is the same across all components,
but the current is divided among the different paths. The total resistance is calculated
using the formula:

1 1
=
𝑅𝑇 1 1 1
+ + ⋯+
𝑅1 𝑅2 𝑅𝑛
In this case, Ohm's Law also allows determining the total current supplied by the
source and how it is distributed among the branches of the circuit.

Although Ohm's Law applies to a wide range of situations, it does not always hold in
all materials or under all conditions. Materials that follow Ohm's Law are known as
ohmic materials, and their resistance remains constant regardless of the voltage or
current. However, some materials do not follow this linear relationship between
current and voltage. Examples include semiconductors, such as diodes and
transistors, whose resistance varies with temperature, the intensity of the electric
field, or the frequency of the signal. In such cases, more complex models than the
classical Ohm's Law are required for analysis.

Ohm's Law integrates with other principles and laws of physics for the analysis of
electric circuits, such as Kirchhoff's Laws. These laws allow extending the analysis
of circuits to more complex situations involving multiple voltage sources and current
branches. Kirchhoff's Current Law states that the sum of the currents entering and
leaving a node in a circuit equals zero. Kirchhoff's Voltage Law states that the
algebraic sum of the voltages in a closed loop of a circuit equals zero. Both laws
complement Ohm's Law, allowing a detailed and comprehensive analysis of complex
electric circuits.

Ohm's Law has numerous practical applications in areas such as electrical and
electronic circuit design, where it helps in selecting components with the appropriate
characteristics to ensure the correct operation of a device. In power distribution
systems, it is used to calculate voltage drops and efficiency in energy transmission.
It is also fundamental in troubleshooting electrical faults, as it helps detect abnormal
values of current, voltage, or resistance in engineering systems. Additionally, in
consumer electronics, from mobile phones to household appliances, Ohm's Law is
crucial in power supply design and ensuring the proper functioning of components.

Página 4
1. Voltage dependence.

Without turning on the voltage source yet, set the potentiometer value to 2.5KΩ.
Assemble the circuit illustrated in Figure 2.1. Once the circuit is assembled, turn on
the voltage source, and vary its value from zero to 15 V, according to what is
requested in table 2.1.

We had to measure the electric current in Amperes, for this we did a circuit with a
potentiometer of 2.5K Ohms and a resistor of 1K Ohm, we put the potentiometer
and resistor in series, then the resistance was in series. For put the Amperemeter
we put it in series with the potentiometer and the voltage source. We measured the
electric current for each value in the table from 0 to 15 volts. Also, we had to
calculate the electric current for each voltage in the table.

For calculate the current we used the formula

𝑉
𝐼=
𝑅
Formula (1)

Where:

I = Electric current (Ameperes)

V = Voltage (Volts)

R = Resistance (Ohms)

Página 5
 Figure 2.1 Circuit to demonstrate voltage dependency.

Table 2.1 Measured values of the circuit in Fig. 2.1.

Voltage Current value Current value Simulated
source (V) (measured) (calculated) current value

𝑉 𝑉
𝐼= = 𝑅𝑇
3.5 𝑘𝛺
0 0 0 0

1 0.2717 mA 0.2857 mA 0.2806mA

2 0.549 mA 0.5714 mA 0.571mA

3 0.8245 mA 0.8571 mA 0.830mA

4 1.099 mA 1.1428 mA 1.110mA

5 1.3742 mA 1.4285 mA 1.250mA

6 1.647 mA 1.7142 mA 1.670mA

7 1.923 mA 2 mA 2mA

8 2.198 mA 2.2857 mA 2.300mA

9 2.4738 mA 2.5714 mA 2.500mA

10 2.749 mA 2.8571 mA 2.859mA

11 3.023 mA 3.1428 mA 3.100mA

12 3.299 mA 3.4285 mA 3.300mA

13 3.576 mA 3.7142 mA 3.600mA

14 3.8525 mA 4 mA 4mA

Página 6
 15 4.1130 mA 4.2857 mA 4.150mA

From table 2.1, and with the values obtained of current (measured) draw the following graph:

Página 7
Simulation. Measuring electric current of the potentiometer , using Multisim 8.

Página 8
2. Dependence on resistance.

With the voltage source off, set the potentiometer value to 0 Ω. Assemble the circuit
illustrated in Figure 2.2. Once the circuit is assembled, turn on the voltage source and
set it to 15 V; Then vary the value of the potentiometer¹ according to what is requested
in Table 2.2:

We had to measure the electric current, we did the same circuit that at the before point,
but in this case the values that change were of the potentiometer, we move the
potentiometer from 0 to 2500 Ohms and put the voltage source in 15 Volts. Also, we put
the Ammeter in series like the before case

¹ Remember that to measure resistance you have to turn off the voltage source, or
otherwise disconnect the potentiometer.

Figure 2.2 Circuit to demonstrate the resistance dependence

Página 9
Table 2.2 Measured values of the circuit in Fig. 2.2

Value of Value of Current value Current value

potentiometer resistance
(measure) (calculated) Simulated
Total = (Pot. + current values
𝑉 15 𝑉
R)
𝐼= =
𝑅𝑇 𝑅𝑇
0Ω 1 kΩ 14.93 mA 15 mA 14.98mA

250Ω 1.25 kΩ 11.81 mA 12 mA 11.91mA

500Ω 1.5 kΩ 10.029 mA 10 mA 10mA

750Ω 1.75 kΩ 8.614 mA 8.5714 mA 8.44mA

1000Ω 2 kΩ 7.54 mA 7.5 mA 7.29mA

1250Ω 2.25 kΩ 6.670 mA 6.666 mA 6.60mA

1500Ω 2.5 kΩ 5.997 mA 6 mA 5.90mA

1750Ω 2.75 kΩ 5.422 mA 5.4545 mA 5.57mA

2000Ω 3 kΩ 4.988 mA 5 mA 5.20mA

2250Ω 3.25 kΩ 4.621 mA 4.6163 mA 4.40mA

2500Ω 3.5 kΩ 4.275 mA 4.2857 mA 4.121mA

Página 10
 From the table above, and with the values obtained of current (measured), draw the following graph:

Simulation. Measuring electric current of the potentiometer , using Tinker Cad.

Página 11
3. Calculation of the power in the resistors.
Before connecting the source you have to set it to 1 V, then turn it off and assemble the circuit
illustrated in figure 2.3, for this circuit use the resistance of 1K Ω at 1/2 watt, once armed turn
on the voltage source.

Figure 2.3 Circuit to demonstrate the effects of resistance on the power absorbed by a circuit element.

For this experiment, we used a 1K Ohm resistor. The voltage source was set to 1 V, 10 V, and 23 V, and the
ammeter was connected in series with the resistor and the voltage source. Then, we calculated the electrical
power.

To calculate the electrical power, we applied the following formula:

P=VI

Simulation . Measuring electric current in resistance of 1K Ohm and amperemeter in

series with the resistance and voltage source, using Tinker Cad.

Página 12
QUESTIONER:

What is the value of the current? I = 1 V I= 10 V I = 23 V

What is the value of the power that dissipates resistance? P = 1mW. P = 100mW. P=529mW.

What effect happened on the resistance, (if you don't see any effect increasing the voltage of the source to 10V and
then to 23V)? R= It started to get very hot, and if you got a little closer you could smell something burning..

Why? R= Because the voltage increase became more than the resistance could handle.

Again, assemble the previous circuit ², but now using the resistance of 1Ω to 1 watt, before connecting the
voltage source make sure that it is fixed to
1 volt and that the ammeter is at the maximum scale.

What is the value of the current? I = 0.42A I = 0.87 A I = 1.27 A

What is the value of the power that dissipates resistance? P = 0.42 W P = 1.71 W P = 3.86 W

What effect happened on the resistance, (if you do not observe any effect increase the voltage of the source to 2V and
if necessary afterwards to 3V)? R = The resistance began to smell like burning and the legs of the resistance began to
turn darker.

What is the difference with the previous circuit? R = That the resistance is of greater power and lower capacity

Why? R = A lower capacity resistor lets more electrons flow.

² Remember that the protoboard is not used in this circuit.

Página 13
Conclusions

Barranco García Kevin Alexis

A solid understanding of Ohm's Law is essential in electronics. This law explains that the current flowing
through a conductor between two points is directly proportional to the voltage across them and inversely
proportional to the resistance. It serves as the foundation for calculating and measuring resistors in circuits.
By using techniques like multimeter readings and interpreting color codes, professionals can accurately
determine resistor values, enabling precise circuit configurations, voltage division, and current regulation.

Bazán Tehuitzil Oscar Damián

This practice provided me a clear understanding of Ohm's Law, demonstrating the direct relationship
between voltage, current, and resistance. By comparing measured and calculated values, I confirmed the
law's accuracy. Additionally, the practice highlighted the importance of selecting appropriate resistors to
prevent overheating, reinforcing key concepts in circuit design and analysis.

Aguilar Olguin Luis Felipe

The experiment on current measurement and Ohm's Law demonstrated the direct relationship between
voltage, current, and resistance. The measurements taken confirmed that increasing resistance results in a
decrease in current, supporting Ohm's Law. This activity not only reinforced our theoretical understanding but
also enhanced our practical skills in using measuring instruments.

IV . BIBLIOGRAPHY.

1. All About Circuits. (2023). Ohm's Law. https://www.allaboutcircuits.com/textbook/direct-current/chpt-2/ohms-

law/
2. SparkFun. (2023). What is Ohm's Law?. https://learn.sparkfun.com/tutorials/what-is-ohms-law/all
3. Electronics Tutorials. (2023). Ohm’s Law and Power. https://www.electronics-
tutorials.ws/dccircuits/dcp_2.html
4. Electrical4U. (2023). Ohm’s Law - Definition, Formula, and Application.
https://www.electrical4u.com/ohms-law/
5. Khan Academy. (2023). Ohm's Law and Circuits with Resistors.
https://www.khanacademy.org/science/physics/circuits-topic/circuits-resistance/a/ee-ohms-law

Página 14
V.-Annexes

Página 15
Página 16
Página 17
Página 18