Ohm's Law: Definition, Formula, Limitations and Applications

What Is Ohm’s Law? 

Ohm’s law is one of the basic fundamental laws in electrical engineering. Ohm’s law defines the relationship between electric current, voltage or potential difference and resistance.

Statement: Ohm’s law states that the voltage or potential difference across the conductor is directly proportional to the electric current flowing through it, provided at a constant temperature or the physical property remains the same.

In other words, the current flows through the conductor between two ends/points is directly proportional to the voltage or potential difference across the two ends/points.

Ohm’s Law Formula

Mathematically, ohm’s law can be expressed as

                                           V α I

       or

                               I α V 

Introducing the constant of proportionality, the resistance in the above equation, we get

                                          V = IR

Where, V = Voltage across the conductor, V

 I = current flowing through the conductors, A

R = Resistance offered by the conductor to flow of current, Ω

This relationship was derived by German physicist George Simon Ohm in January 1781. That’s why it is known as Ohm’s law.

George Simon Ohm

When a voltage or potential difference across the conductor is known with known resistance then the current the conductor is given by,

                                                                    I =  V/R

When a current through the conductor is known with known resistance then the voltage across the conductor is given by,

                                                                    V = IR

Similarly, when a current through the conductor and voltage across the conductor is known then the unknown resistance can be found by,

                                                                     R =  V/I

Ohm's Law Triangle

Ohm’s Law is Not Applicable To or Limitations of Ohm’s Law

Some of the limitations of ohm’s law are given below:

• Ohm's Law is not applicable to the following non-linear elements. 

1. Resistance 2. Capacitance 3. Semiconductors 4. Vacuum Tubes 5. Electrolytes 6. Carbon Resistors 7. Arc Lamps

Note that Non-Linear elements are those in which the relation between the current and the voltage is non-linear i.e., the current is not exactly proportional to the applied voltage. 

• Ohm's law is also not applicable to the unilateral networks.

Note that a unilateral network contains unilateral elements such as transistors, diode, etc. A unilateral elements are those that allow the flow of current only in one direction. Hence ohm's law is not applicable to unilateral networks. 

Applications of Ohm’s Law

Some of the applications of ohm’s law are given below:

• To calculate the unknown potential difference or voltage, resistance, and flow of the current of an electric circuit.  
• Ohm’s law is used in an electronic circuit to determine the internal voltage drop across the electronic components. 
• Ohm’s law is used in DC measuring circuits particularly in DC ammeter in which a low resistance shunt is used to divert the current.