Glossary
Conductor (in electric field)
A material containing free charges that can move readily, resulting in zero electric field inside the material when in electrostatic equilibrium.
Example:
When a copper wire, a conductor, is placed in an external electric field, charges redistribute on its surface until the internal field is nullified.
Coulomb's Constant
A proportionality constant, denoted by 'k', used in Coulomb's Law and electric field equations, relating the force between charges to their magnitudes and separation.
Example:
When calculating the electric field from a point charge, you'll always use Coulomb's constant, approximately 9 x 10^9 Nm^2/C^2.
Electric Field
A region of space around a charged object where another charged object would experience a force. It mediates the interaction between charges.
Example:
When you rub a balloon on your hair, it gains a charge and creates an electric field around it, which can then attract small pieces of paper.
Electric Field Strength (E = Fe/q and E = kQ/r^2)
A quantitative measure of an electric field at a point, defined as the force per unit positive test charge or derived from a source charge and distance.
Example:
If a 2 C charge experiences a 10 N force in a field, the electric field strength at that point is 5 N/C.
Electrostatic Equilibrium
The state where there is no net motion of charge within a conductor, meaning the electric field inside the conductor is zero and any excess charge resides on its surface.
Example:
A metal sphere that has been charged and then left undisturbed will eventually reach electrostatic equilibrium, with all excess charge distributed evenly on its outer surface.
Electrostatic Force (F = qE)
The force experienced by a charge placed within an electric field, calculated as the product of the charge's magnitude and the electric field strength.
Example:
A proton moving through a uniform electric field will experience a constant electrostatic force, causing it to accelerate.
Faraday Cage
An enclosure made of a conductive material that blocks external static and non-static electric fields, protecting its interior from electromagnetic radiation.
Example:
During a lightning storm, being inside a car acts as a Faraday cage, protecting occupants from the high voltage outside.
Field Lines
Imaginary lines used to visualize an electric field, indicating the direction of the force on a positive test charge and whose density represents the field's strength.
Example:
Drawing field lines around a positive point charge shows them radiating outwards, while around a negative charge, they point inwards.
Insulator (in electric field)
A material in which charges are tightly bound and cannot move freely, allowing an electric field to exist within the material.
Example:
Glass, an insulator, can hold a static charge on its surface because electrons are not free to move and dissipate the charge.
Parallel Plates
Two conductive plates placed parallel to each other, typically carrying opposite charges, which create a uniform electric field between them.
Example:
Capacitors often consist of parallel plates to store electrical energy by creating a consistent electric field.
Point Charges
Idealized charged objects considered to have negligible size, from which electric fields extend radially.
Example:
Calculating the electric field at a specific distance from a single electron often treats the electron as a point charge.
Polarization
The process by which an external electric field causes a slight separation of positive and negative charge within a neutral atom or molecule, creating an induced dipole.
Example:
When a charged comb is brought near small pieces of paper, the paper becomes polarized, leading to an attractive force even though the paper is neutral overall.
Superposition of Electric Fields
The principle stating that the net electric field at any point due to a collection of charges is the vector sum of the electric fields produced by each individual charge.
Example:
To find the total electric field at the center of a square with charges at each corner, you would use the superposition of electric fields by adding the vector contributions from all four charges.
Test Charge
A hypothetical, infinitesimally small positive charge used to determine the direction and magnitude of an electric field at a given point without disturbing the field itself.
Example:
To map the electric field around a charged sphere, one would conceptually place a test charge at various points and observe the force it experiences.