Electric Field Strength (E)
Electric Field Strength (E) is a vector quantity that describes the force per unit charge experienced by a positive test charge at a specific point in space. It defines the intensity and direction of an electric field and is measured in volts per meter (V/m) in the SI system.
Electric Field Strength vs. Electric Potential
Electric field and electric potential are closely related but describe different physical concepts. The relationship is defined by:
E = –∇V
Where:
∇V is the spatial gradient of the electric potential
The negative sign indicates that the electric field points from higher to lower potential
This means the electric field describes how rapidly the potential changes in space.
Formulas for Electric Field Strength
Point Charge:
For a point charge Q in free space:
E = k × Q / r²
Where:
k = 8.99 × 10⁹ N·m²/C² (Coulomb's constant)
Q = Electric charge (C)
r = Distance from the charge (m)
Uniform Field (parallel plates):
In a homogeneous field between two charged plates:
E = V / d
Where:
V = Potential difference (V)
d = Distance between the plates (m)
These expressions apply in theoretical and practical electrical setups such as capacitors and electrostatic systems.
Example Calculation
Given a point charge of 1 μC (1 × 10⁻⁶ C) at 1 m distance in vacuum:
E = (8.99 × 10⁹) × (1 × 10⁻⁶) / (1)² = 8,990 V/m
This illustrates the inverse-square nature of electric field strength from point sources.
Applications of Electric Field Strength
Electric field strength is fundamental to numerous domains:
Electrical Engineering: High-voltage systems, insulation design, power distribution
Electronics: Design and simulation of semiconductors and ICs
Medical Technology: Techniques like electrophoresis and electron microscopy
Materials Science: Analysis of dielectric materials and polarization behavior
Telecommunications: Field distribution near antennas and RF propagation modeling
Particle Physics: Field control in accelerators and charged-particle experiments