Glossary
Charge Distribution (on conductors)
The way excess charge arranges itself on a conductor; in electrostatic equilibrium, it resides entirely on the outer surface.
Example:
If you place a charge on a hollow metal sphere, the charge distribution will be uniform on its outer surface, with no charge inside.
Charged Objects
Objects that possess a net positive or negative electric charge due to an imbalance of protons and electrons.
Example:
A plastic comb rubbed with wool becomes a charged object and can attract small pieces of paper.
Conductor
A material, typically a metal, in which electric charges (electrons) are free to move easily throughout its volume.
Example:
Copper wire is an excellent conductor because its electrons are not tightly bound to individual atoms and can flow easily.
Direction of Electric Fields
The convention that electric field lines point radially outward from positive charges and radially inward towards negative charges, indicating the direction a positive test charge would accelerate.
Example:
Near a positively charged sphere, the direction of electric fields would be away from the sphere, like spokes on a wheel.
Electric Field Line Diagrams
Visual representations using continuous lines to show the direction of the electric field (tangent to the lines) and its strength (indicated by the density of the lines).
Example:
An electric field line diagram for a parallel plate capacitor would show evenly spaced, parallel lines between the plates, indicating a uniform field.
Electric Field Vector (E)
A vector quantity representing the electric field at a specific point, defined as the electric force experienced by a tiny positive test charge divided by the magnitude of that charge.
Example:
To determine the force on an electron at a specific location, you'd multiply its charge by the electric field vector at that point.
Electric Fields
Invisible force fields surrounding charged objects that exert forces on other charges, representing the 'force per charge' at any point in space.
Example:
When you rub a balloon on your hair, it gains a charge and creates an electric field that can make your hair stand on end.
Electric Force (F)
The fundamental force of attraction or repulsion between any two charged particles or objects.
Example:
The attraction between a positively charged proton and a negatively charged electron is an electric force.
Electrostatic Equilibrium
The state of a conductor where all excess charges are at rest, resulting in a zero electric field everywhere inside the conductor.
Example:
When a metal sphere is charged and then left alone, its charges will redistribute until it reaches electrostatic equilibrium, and the field inside is zero.
Fixed Charges (in insulators)
Electric charges within an insulator that are not free to move and remain localized where they are placed or induced.
Example:
When you rub a balloon, the fixed charges on its surface stay put, allowing it to stick to a wall.
Insulator
A material, such as rubber or glass, in which electric charges are tightly bound to atoms and cannot move freely.
Example:
The plastic casing around an electrical wire acts as an insulator, preventing current from flowing where it shouldn't.
Internal Fields (of conductors and insulators)
The electric field within a material; it is zero inside a conductor in electrostatic equilibrium but can be non-zero inside an insulator.
Example:
If you are inside a Faraday cage, the internal field is zero, protecting you from external electric fields.
Net Electric Field
The total electric field at a given point, determined by the vector sum of all individual electric field vectors produced by multiple charges present.
Example:
If you have two point charges, one positive and one negative, the net electric field at a point between them will be the vector sum of the fields from each charge.
Surface Fields (of conductors)
The electric field existing just outside the surface of a charged conductor, which is always perpendicular to the surface at that point.
Example:
When lightning strikes a car, the surface fields on the car's exterior are perpendicular to the metal, guiding the charge around the occupants.
Test Charge (q)
A hypothetical, infinitesimally small positive charge used conceptually to probe and measure the electric field at a point without significantly altering the field being measured.
Example:
To map the electric field around a charged sphere, physicists imagine placing a tiny test charge at various points and observing the force it experiences.
Vector Field Maps
Diagrams that use arrows of varying lengths and directions at different points in space to visually represent the magnitude and direction of an electric field.
Example:
A vector field map around a dipole would show arrows pointing away from the positive charge and towards the negative charge, with longer arrows closer to the charges.