Glossary
Charge Density
A measure of how much electric charge is distributed per unit length, area, or volume within a material.
Example:
A uniformly charged insulating sphere has a constant volume charge density, meaning charge is spread evenly throughout its volume.
Electric Flux
A measure of how much of an electric field passes through a given area, representing the number of electric field lines piercing a surface.
Example:
When a uniform electric field passes perpendicularly through a flat screen, the electric flux is simply the product of the field strength and the screen's area.
Enclosed Charge (Qenc)
The total electric charge contained within a chosen closed Gaussian surface.
Example:
If a spherical Gaussian surface encloses a point charge of +5 nC, then the enclosed charge is +5 nC, regardless of any charges outside the sphere.
Gauss's Law
A fundamental law in electromagnetism that relates the total electric flux through any closed surface to the net electric charge enclosed within that surface.
Example:
Using Gauss's Law, one can easily determine the electric field produced by a uniformly charged sphere without complex integration.
Gaussian Surface
An imaginary closed surface chosen strategically to simplify the calculation of electric flux and apply Gauss's Law.
Example:
To find the electric field of an infinitely long charged wire, a cylindrical Gaussian surface is the ideal choice due to its symmetry.
Net Flux
The total electric flux through a closed surface, calculated as the sum of all flux entering and exiting the surface.
Example:
For a closed box with no charge inside, the total number of field lines entering equals the number exiting, resulting in a net flux of zero.
Permittivity of Free Space (ε₀)
A fundamental physical constant representing the ability of a vacuum to permit electric field lines, appearing in Coulomb's Law and Gauss's Law.
Example:
The value of permittivity of free space is crucial when calculating the electric field strength in a vacuum using Gauss's Law.
Sign Convention (for flux)
A rule stating that electric field lines entering a closed surface contribute negative flux, while lines exiting contribute positive flux.
Example:
If an electric field points inward towards a spherical surface, the flux through that surface will be negative according to the sign convention.