Limitations of Ohm's Law: Explanation & Example

Limitations of Ohm's Law Overview

Ohm's law is a fundamental principle of electrical engineering that provides a mathematical relationship between current, voltage, and resistance in an electrical circuit. This law has been widely used and accepted as a basic tool for understanding and analyzing electrical systems for over a century. Although it is widely used in electrical engineering, there are certain limitations to Ohm's law that must be considered. Read the article till the end to learn about these limitations of Ohm's law.

What is Ohm's Law?

Ohm's law is a fundamental principle of electrical engineering that describes the relationship between electric current, voltage, and resistance in a circuit. It is named after the German physicist Georg Simon Ohm, who first formulated the law in 1827.

Ohm's law states that the current (I) flowing through a conductor between two points is directly proportional to the voltage (V) across the two points and inversely proportional to the resistance (R) between them. The mathematical expression for Ohm's law is given by:

V = IR, where V is the voltage, I is the current, and R is the resistance(V ∝I) 

Or, it can be represented as follows: 

I = V/R or V = R*I

This relationship can also be represented graphically as a straight line on a voltage-current graph.

Limitations of Ohm's Law

The limitations of Ohm's law are very important to learn as it helps the engineers and technicians to avoid common mistakes and ensure that their calculations and models are accurate. This is particularly important in the design and analysis of electrical systems, where even small errors can have significant consequences.

The most important limitations of Ohm's law are as follows:

1. Ohm's law only applies to conductors with a constant resistance:It assumes that the resistance of the conductor remains constant, regardless of the current flowing through it. This is only true for some materials, and for others, the resistance changes with temperature or current.
2. Does not apply to non-linear materials:Ohm's law assumes a linear relationship between voltage and current, which is only true for some materials. For non-linear materials, such as diodes and transistors, the relationship between voltage and current is not proportional.
3. Resistance changes with temperature:The resistance of some materials can change with temperature, which can impact the accuracy of Ohm's law calculations.
4. Does not account for magnetic fields: Ohm's law does not consider the impact of magnetic fields on electrical circuits, which can affect the behavior of the circuit.
5. Does not account for circuit dynamics:Ohm's law is a steady-state law, meaning it assumes that the circuit has reached a steady state and that the current, voltage, and resistance are not changing. This may not always be the case in dynamic circuits, where the current and voltage are constantly changing.

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Examples of limitations of Ohm's Law

1. The limitations of Ohm's law are demonstrated via a diode. When the voltage and current graph for a diode is shown, it can be seen that the relationship between current and voltage is not linear. The relationship between current and voltage is not linear. This occurs when voltage is indicated in the opposite way from how it should be, fixing the magnitude. As a result, the current is generated at a different magnitude and in the opposite direction.
2. Ohm's law does not apply to a water volt-ammeter because it is a unilateral network.
3. Additionally, not all conductors need to abide by Ohm's law. Silicon and germanium semiconductors do not adhere to Ohm's law. They are regarded as non-ohmic conductors as a result.

How are the limitations of Ohm's Law useful?

The limitations of Ohm's law are useful in improving the accuracy, understanding, and design of electrical systems. Recognizing and understanding these limitations can help electrical engineers and technicians make informed decisions and achieve better results in their work.

The limitations of Ohm's law are useful in several ways:

1. Improved accuracy:Understanding the limitations of Ohm's law can help electrical engineers and technicians to avoid making common mistakes in their calculations and models. This can lead to more accurate and reliable results, especially in complex electrical systems.
2. Better understanding of other electrical laws:Many other electrical laws are based on Ohm's law, and understanding the limitations of Ohm's law can provide valuable insights into the limitations of these other laws.
3. Real-world applications: Recognizing the limitations of Ohm's law can help engineers and technicians to make informed decisions when designing and analyzing electrical systems. For example, knowing that Ohm's law is not applicable to non-linear materials can help engineers to choose appropriate models and techniques to analyze these systems.
4. Improved design: Understanding the limitations of Ohm's law can lead to more creative and innovative design solutions, especially in cases where Ohm's law is not applicable.

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Limitations of Ohm's Law: Application in Daily Life

Ohm's law may be used to calculate a circuit's resistance, current, and voltage applied to the circuit. We may determine the values of additional parameters, such as resistivity and many more, using the three values mentioned above. Ohm's Law's practical uses include:

1. In Fuses:Circuit breakers and fuses are both used to safeguard a circuit. These are linked to the electrical appliances in series. We can determine the potential current via the fuses using Ohm's law. If the current value is excessive, it might harm the circuit and possibly cause the electrical equipment to explode.
2. To control the speed of fans:we may adjust the speed of the fans in our homes by moving the regulator from the start to the finish. Here, the current passing through the fan is governed by the regulator's control of the resistance. Ohm's Law allows us to calculate the resistance, current, and power flowing for any given input value.
3. To determine power consumption:the electrical heaters contain a high-resistance metal coil that permits a specific amount of current to pass through it to generate the required heat. This rule is used to determine how much electricity should be provided to the heaters.
4. To determine the size of resistors: Electric appliances such as kettles and irons have many resistors. The resistors limit the amount of current that may pass through them to create the requisite quantity of heat. The size of the resistors contained in them is determined by applying Ohm's law.

 Limitations of Ohm's Law: Components 

Ohm's Law states that the current flowing through a conductor between two points is directly proportional to the voltage across the two points and inversely proportional to the resistance of the conductor. The three components of Ohm's Law are:

1. Voltage (V): It is the electrical potential difference between two points, also known as electromotive force (EMF). It is measured in volts (V). The voltage across a conductor drives the electric current through it.
2. Current (I):It is the flow of electric charge through a conductor. It is measured in amperes (A). Current is determined by the voltage across the conductor and the resistance of the conductor.
3. Resistance (R):It is the measure of the opposition to electric current in a conductor. It is measured in ohms (Ω). The resistance of a conductor determines how much current will flow through it when a certain voltage is applied. The higher the resistance, the lower the current flow.

These three components are related by Ohm's Law, which states that the current flowing through a conductor between two points is equal to the voltage across the two points divided by the resistance of the conductor (I = V/R).

Limitations of Ohm's Law: Formula for finding the Value of Resistance

It is the constant ratio that gives the unknown values of resistance. For a wire of uniform cross-section, the resistance depends on the length l and the area of the cross-section A. It also depends on the temperature of the conductor. At a given temperature the resistance,

R = ρlA

where ρ denotes the specific resistance or resistivity and is characteristic of the material of the wire. Using the last equation,

V = I × R = IρlA

I/A is the current density and is denoted by j. The SI unit of current density is A/m². So,

E I = j ρ I

This can be written as E = j ρ or j = σ E, where σ is 1/ρ is conductivity.

Limitations of Ohm's Law: Things to Remember

1. Ohm's law assumes a linear relationship between voltage and current, which is not always the case in real-world electrical systems.
2. The resistance of some materials can change with temperature, frequency, or magnetic fields, which can impact the accuracy of Ohm's law calculations.
3. Ohm's law assumes that the circuit has reached a steady state and that the current, voltage, and resistance are not changing. This may not always be the case in dynamic circuits.
4. Ohm's law does not consider the impact of magnetic fields on electrical circuits.
5. The limitations of Ohm's law can impact the accuracy of electrical calculations and models, and alternative methods or models may need to be used when Ohm's law is not applicable.
6. Understanding the limitations of Ohm's law can help improve the accuracy, understanding, and design of electrical systems, and lead to more informed decisions in electrical engineering and technology.

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