Glossary
Coulomb (C)
The SI unit of electric charge, representing the amount of charge transferred by a constant current of one ampere in one second.
Example:
A typical lightning bolt can transfer several coulombs of charge between the cloud and the ground.
Coulomb's Constant (k)
A proportionality constant in Coulomb's Law, representing the strength of the electrostatic force in a vacuum.
Example:
The value of Coulomb's constant is approximately 8.99 × 10^9 N·m²/C², indicating the immense strength of electrostatic interactions.
Coulomb's Law
A fundamental law describing the electrostatic force between two point charges, stating that the force is directly proportional to the product of the charges and inversely proportional to the square of the distance between them.
Example:
Coulomb's Law explains why two positively charged protons in an atomic nucleus strongly repel each other.
Electric Charge
A fundamental property of matter that causes it to experience a force when placed in an electromagnetic field. It exists in two types: positive and negative.
Example:
When you rub a balloon on your hair, you transfer electric charge, causing the balloon to stick to a wall due to electrostatic attraction.
Electric Field
A vector field that surrounds an electric charge and exerts a force on other charges within its region; its direction is defined by the force on a positive test charge.
Example:
The electric field around a charged Van de Graaff generator causes nearby hair strands to stand on end.
Electric Flux
A measure of the electric field passing through a given surface, calculated as the product of the electric field component perpendicular to the surface and the surface area.
Example:
The electric flux through a closed surface enclosing a charge is constant, regardless of the surface's shape, as described by Gauss' Law.
Electric Potential
The electric potential energy per unit charge at a specific point in an electric field, representing the potential for work to be done on a charge at that location.
Example:
Points closer to a positive charge have a higher electric potential, similar to how objects at a higher elevation have greater gravitational potential.
Electric Potential Difference (Voltage)
The work done per unit charge to move a test charge between two points in an electric field; it is a scalar quantity.
Example:
A car battery provides an electric potential difference of 12 volts, pushing charge through the car's electrical system.
Electrostatics
The branch of physics that studies electric charges at rest and the forces, fields, and potentials associated with them.
Example:
Understanding electrostatics is crucial for designing devices like photocopiers, which rely on stationary charges to attract toner particles to paper.
Gauss' 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:
Gauss' Law can be used to easily calculate the electric field produced by highly symmetric charge distributions, such as a uniformly charged sphere.
Gaussian Surface
An imaginary closed surface chosen to simplify the calculation of electric fields using Gauss' Law, typically selected to exploit the symmetry of the charge distribution.
Example:
To find the electric field of an infinitely long charged wire, one would choose a cylindrical Gaussian surface coaxial with the wire.
Permittivity of Free Space (ε₀)
A fundamental physical constant representing the ability of a vacuum to permit electric field lines, used in Coulomb's Law and Gauss' Law.
Example:
The permittivity of free space is a crucial constant that determines the strength of electric interactions in a vacuum.
Principle of Superposition
States that the net electric field or potential at a point due to a collection of charges is the vector sum (for fields) or algebraic sum (for potentials) of the fields or potentials due to individual charges.
Example:
To find the total electric field at a point near multiple point charges, you apply the principle of superposition by adding the individual electric field vectors from each charge.
Relationship between Electric Field and Electric Potential
The electric field is the negative gradient of the electric potential, meaning it points in the direction of the steepest decrease in potential.
Example:
If you map out the relationship between electric field and electric potential, you'll find that electric field lines always point 'downhill' from high potential to low potential.
Symmetry (in electrostatics)
The property of a charge distribution that allows for simplification of electric field and potential calculations, often by choosing an appropriate Gaussian surface.
Example:
Exploiting the spherical symmetry of a charged sphere allows for a straightforward application of Gauss' Law to find its electric field.
Volt (V)
The SI unit of electric potential difference, defined as one joule of work per coulomb of charge.
Example:
A standard household outlet typically provides 120 volts of electric potential difference.