Ohm’s Law in Detail

Ohm’s Law establishes the relationship between the current (I) and the voltage (V) existing between two points of a conductor. German physicist Georg Ohm presented this law to the world. He was the person to quantify the voltage and current by conducting experiments with circuits having different lengths of wires. Ohm derived a complex form of the equation through which he gave an explanation of the results of his experiments. There are several other forms of Ohm’s Law. Electromagnetics, material sciences, etc. are some branches of modern physics where we use Ohm’s Law but in different forms.

Statement of Ohm’s Law

Ohm’s Law depicts that when the current flows through a conductor between its two ends, it is directly proportional to the voltage that we apply between the two points. 

Here, we use a constant ‘R’ to remove the sign of proportionality. This constant is known as ‘resistance’. The mathematical equation is given below:

I=V/R

where I = Current through the conductor (Ampere)

V = Voltage measured (Volts)

R = resistance of the conductor (Ohm). resistance ‘R’ doesn’t depend on the current.

Applicability of Ohm’s Law

It is applicable only in the case of conductors. Ohm’s Law is not applicable to insulators. The materials that obey Ohm’s law are called ‘ohmic’, and those that don’t obey this law are called ‘non-ohmic’ materials.

Effect of Temperature

Ohm’s Law states the straightly proportional relationship of voltage to the current flowing through the conducting material. We use a constant to remove the sign of proportionality, in the equation. From Ohm’s Law, we come to know that this constant is the ‘resistance’ of the conductor. Many types of research have shown that the resistance is directly proportional to the length of the conducting material. It has also been shown that the resistance is inversely proportional to the area of the cross-section of the conducting material. In this case, also, we need a constant in the equation to remove the sign of proportionality. The constant we need here is known as the ‘Resistivity’ of the material. 

The resistivity relies on the kind of material taken in use. It is expected to give a constant value. The resistivity of certain materials may vary with the change in their temperature. In the case of conductors, resistivity increases when we increase the temperature. But in the case of semiconductors, it decreases when we increase the temperature. In this way, resistivity plays the role of a variable that further makes the resistance also a variable and in this way certifies Ohm’s Law as wrong. The only criterion that turned the resistivity into a variable was the temperature. That is why the temperature is taken as constant in this case. The factor that makes the resistivity constant is the constant temperature. It also makes the resistance constant. This constant resistance is needed to make Ohm’s Law applicable. This is the reason why Ohm’s Law is applicable only at a constant temperature.

Scope of Ohm’s Law

Ohm’s Law is not universal. It has many limitations. Scientists have observed  Ohm’s law on a broad spectrum. Through many successful experiments at the atomic level, it has been proven that this law works at the atomic level too.

Usage in Circuit Analysis

We can use different forms of the same equation of Ohm’s Law in circuit analysis. The forms are given below-

I=V/R or V=IR or R=V/I

• In resistive circuits – Ohm’s Law applies to resistive circuits. This law applies to all (DC, AC) current forms. These are the cases where Ohm’s Law is valid.

• In reactive circuits – As Ohm’s Law has only resistance (R), it is not directly applicable here in the complex form of the equation of reactive circuits.

• In linear approximations – Ohm’s Law is also used in the various methods of linear approximations.

Conclusion

Through the above discussion, we can answer all fundamental questions about our topic like ‘State Ohm’s Law’ or ‘Where can we apply Ohm’s Law?’ or ‘Which scenarios is Ohm’s Law not applicable to?’ etc. This law is one of the most fundamental laws governing electrical and electronic circuits. It is used within all branches of electrical and electronic science. It calculates the value of resistors required in circuits and determines the current flowing in a circuit where the voltage can be measured easily across a known resistor. Moreover, Ohm’s Law is used in many calculations in all forms of electrical and electronic circuits, almost anywhere that current flows.