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Electric current is the rate of flow of electric charge through a conductor or circuit.

It tells us how much charge passes a given point per unit time.

It is denoted by the symbol I and measured in amperes (A).

Mathematically, it is defined as:

I = Q/t

where:

I= current (in amperes, A)

Q= charge (in coulombs, C)

t = time (in seconds, s)

In simple terms:
Electric current is the movement of electrons through a wire or any conductive material.
A higher current means more electrons are flowing per second.

Example:
If 2 coulombs of charge pass through a wire in 1 second, the current is:

I = 2/1= 2 amperes

Voltage is the electric potential difference between two points in a circuit.

It represents the amount of energy per unit charge needed to move an electric charge from one point to another.

It is denoted by the symbol V and measured in volts (V).

Mathematically, voltage is defined as:

V = W/Q

where:

V= voltage (in volts, V)

W = work done or energy (in joules, J)

Q = electric charge (in coulombs, C)

In simple terms:
Voltage is like the “pressure” that pushes electric charges through a conductor.
A higher voltage means more energy is available to move charges through a circuit.

Example:
A 9-volt battery provides enough electric potential to push current through a small electronic device such as a radio or a remote control.

Resistance is a measure of how much a material or component opposes the flow of electric current through it.

It is denoted by the symbol R and measured in ohms (Ω).

Mathematically, resistance is defined using Ohm’s Law as:

R = v/I

where:

R= resistance (in ohms, Ω)

V = voltage across the material (in volts, V)

I = current through the material (in amperes, A)

In simple terms:
Resistance determines how easily current can pass through a conductor — a higher resistance means less current flows for a given voltage.

Example:

A metal wire has low resistance (current flows easily).

A rubber band has high resistance (current hardly flows).

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

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