P. Classes

Ohm’s Law is one of the most fundamental principles in electrical and electronic engineering. It defines the relationship between voltage (V), current (I), and resistance (R) in an electrical circuit

⚡ Statement of Ohm’s Law

Ohm’s Law states that:

> “The current flowing through a conductor between two points is directly proportional to the potential difference (voltage) across the two points, provided the temperature and other physical conditions remain constant.”

To remove the proportionality, we introduce a constant of proportionality R (resistance):

V = IR

Where:

V = Voltage across the conductor (volts, V)

I = Current through the conductor (amperes, A)

R = Resistance of the conductor (ohms, Ω)

⚙️ Derivation of Ohm’s Law (Conceptual)

Ohm’s Law can be understood or derived from the microscopic behavior of electric charges in a conductor.

Thus,

V = I R

⚡ Graphical Representation

If you plot V (voltage) on the Y-axis and I (current) on the X-axis:

For an ohmic conductor, the graph is a straight line passing through the origin (slope = R).

For non-ohmic materials (like diodes, transistors, etc.), the graph is non-linear.

🧩 Limitations of Ohm’s Law

Ohm’s Law does not hold true when:

Temperature is not constant.

The material is non-ohmic (e.g., semiconductors, vacuum tubes).

The conductor changes its properties with voltage or current (e.g., filament lamps).

✅ Summary

Quantity Symbol Unit Relationship

Voltage V Volt (V)
Current I Ampere (A)
Resistance R Ohm