Coulomb (C)
The coulomb (symbol: C) is the SI unit of electric charge, named after the French physicist Charles-Augustin de Coulomb. It quantifies the amount of electric charge and is fundamental in describing current flow and electrostatic interactions in electrical and electronic systems.
Elementary Charge and SI Definition
The coulomb is defined based on the elementary charge (e) of electrons:
1 coulomb = 6.242 × 10¹⁸ elementary charges
The elementary charge e ≈ 1.602 × 10⁻¹⁹ C
This quantification allows precise modeling of electrical behavior at both macroscopic and subatomic levels.
Coulomb’s Law
Coulomb’s Law describes the electrostatic force (F) between two point charges:
F = k × (Q₁ × Q₂) / r²
Where:
F = Electrostatic force (N)
k = Coulomb’s constant ≈ 8.99 × 10⁹ N·m²/C²
Q₁, Q₂ = Electric charges (C)
r = Distance between charges (m)
This law underpins the analysis of capacitors, electric fields, and charged particle interactions.
Relation to Electric Current
Charge and current are directly related by the equation:
I = Q / t
Where:
I = Electric current (A)
Q = Electric charge (C)
t = Time (s)
This formula helps calculate how much charge flows through a conductor over time.
Example: Charge Calculation
If a current of 2 amperes flows for 10 seconds, the transferred charge is:
Q = I × t = 2 A × 10 s = 20 C
Such calculations are used in circuit design, energy storage systems, and battery monitoring.
Applications Across Disciplines
The coulomb is applied in various scientific and engineering domains:
Electrical Engineering: Circuit design, charge storage, and insulation
Electronics: Semiconductor behavior and signal integrity
Electrochemistry: Battery reactions, electroplating, and Faraday’s laws
Particle Physics: Measuring subatomic particle charge
Medical Technology: ECG/EEG diagnostics and bioelectric signal monitoring
Telecommunications: Signal transmission and line charging effects
Materials Science: Electrostatic discharge (ESD) protection and material properties