A Short Note On Ohm’s Law Limitations

Current, voltage and resistance are the three major primary constituents of electricity. Ohm’s law portrays a straight relationship among such three variables. 

Theory of Ohm’s law

As per Ohm’s law, the voltage or potential distinction between the two locations is proportional to the current of electricity moving via the resistance, and the resistance on the circuit is proportional to the current or electricity moving via the resistance. V=IR is the deemed formula used for Ohm’s law

Establishing the constant of proportionality, namely the resistance, one enters the general mathematical equation that illustrates this association:

I= V/R

Over here, I denote the current throughout the conductor. Its units are in terms of amperes.

V denotes the voltage computed across the conductor measured in units of volts, and R denotes the resistance of the conductor measured in units of ohms. 

More particularly, Ohm’s law determines that the R in this connection is constant, self-sufficient of the current. If there is no constant resistance, the preceding equation will not be called Ohm’s law; however, it could still be employed as an explanation of static/DC resistance. Ohm’s law is an experiential association that precisely explains the conductivity of the huge bulk of electrically conductive substances over numerous orders of the degree of current. Though a few materials do not comply with Ohm’s law, these are known as non-ohmic.

The law was given the name by the German physicist Georg Ohm, who, in a thesis circulated in 1827, explained the dimensions of applied voltage and current via simple electrical circuits comprising different lengths of wire. Ohm clarified his experimental outcomes by a faintly more intricate equation compared to the contemporary form above.

When talked about in physics, the word Ohm’s law is as well utilized to designate numerous simplifications of the law; for instance, the vector form of the law employed in material science and electromagnetics:

J = σE 

Over here, J denotes the current density on a particular position in a resistive material, E denotes the electric field on that position, and σ (sigma) denotes a material-dependent factor known as the conductivity. Such reformulation of Ohm’s law is because of Gustav Kirchhoff.

Ohm’s law limitations

• The law of Ohm is not applicable to unilateral networks. The current could move in one course in unilateral networks. Transistors, Diodes, and extra electronic components are employed in these kinds of networks.
• Non-linear components are moreover off the hook from Ohm’s law. They contain a current which is not proportional to the functional voltage, which connotes that the resistance rate of those components alters relying on the voltage and current. The thyristor is an illustration of this non-linear element.
• Ohm’s law is scrutinized on a broad array of length scales. In the initial 20th century, it was considered that Ohm’s law would not succeed at the atomic range; however, experiments have not abided out this anticipation. Since 2012, researchers have shown that Ohm’s law operates for silicon wires equal to the size of four atoms wide and one atom high.
• Ohm’s law is just pertinent in the case of metallic conductors. Consequently, it won’t operate in the context of non-metallic conductors.

Ohm’s law is not applicable in the following cases

Case-1

The diode is considered to be a non-ohmic power apparatus. This designates that the current moves by the diode do not boost the linear proportion of the augmented voltage. The voltage throughout the exhaustion layer gets constant on raising the applied voltage. Consequently, no additional boost of the voltage through the PN joint is feasible. Nevertheless, the current throughout the diode boosts with a rise in voltage.

Therefore, it is understandable that the diode current does not augment linearly on a rise of applied voltage. Consequently, in this case, Ohm’s law is not valid.

Case-2

When we talk about a luminous lamp, the current throughout the lamp does not augment with a rise in voltage. Why does this occur? The filament resistance augments with the augment in temperature, and therefore the filament lamp contains non-linear traits. In this, Ohm’s law is not appropriate.

Conclusion

Ohm’s Law is one of the elementary and significant laws administering electrical and electronic circuits. It associates current, resistance, and voltage for a linear gadget in a way that if two are recognized, the third can be estimated.

With current, resistance, and voltage acting as three of the main circuit quantities, this implies that Ohm’s Law is, in addition, hugely significant. However, there are a few limitations and drawbacks of Ohm’s law that cannot be ignored.