Electric Charges and Fields - VOCABULARY Flashcards

A set of vocabulary-style flashcards covering key terms and definitions from the Electric Charges and Fields lecture notes.

Charge Quantization

Charge comes in discrete units; the smallest unit is the electron charge e, with Q = n e (n is an integer).

Elementary Charge (Electron Charge)

The magnitude of the charge of an electron, e = 1.6 × 10^-19 C.

Coulomb's Law

The electrostatic force between two point charges is proportional to the product of the charges and inversely proportional to the square of the separation: F = k q1 q2 / r^2 (k = 1/(4π ε0) ≈ 9×10^9 N m^2/C^2).

Electric Field

The region around a charge where a test charge experiences force; E = F/q0; SI unit N/C; direction is the force on a positive test charge.

Test Charge

A small charge used to probe the electric field; the force on it is F = q0 E.

Electric Field Lines

Imaginary lines showing field direction; originate on positive charges and end on negative charges; do not intersect; density relates to charge magnitude.

Superposition Principle (Electrostatics)

The net force on a charge due to multiple charges is the vector sum of the individual forces.

Electric Dipole

A pair of equal and opposite charges separated by a small distance.

Dipole Moment

p = q d; a vector from the negative to the positive charge; magnitude equals the charge times separation distance.

Electric Field on Dipole Axis (Axial)

On the axis of the dipole, E_axial ≈ (1/4πε0) (2p) / r^3; direction along the axis.

Electric Field on Dipole Equator (Equatorial Position)

On the perpendicular bisector, E_eq ≈ (1/4πε0) (p) / r^3; direction opposite to the dipole moment.

Electric Flux

The measure of the net electric field lines crossing a surface: Φ_E = ∮ E · dA; units: Weber (Wb).

Gauss's Law

The net electric flux through a closed surface equals the enclosed charge divided by ε0: ∮ E · dA = Q_enclosed / ε0.

Permittivity and Relative Permittivity

ε0 is vacuum permittivity (~8.85×10^-12 F/m); in a medium ε = ε0 εr, where εr is the relative permittivity (dielectric constant).

Electric Field due to Infinite Line of Charge

E = λ / (2π ε0 r); field strength decreases with distance from the line.

Electric Field due to Large Thin Sheet

For an infinite sheet with surface charge density σ, E = σ / (2ε0) on each side.

Electric Field due to Shell (Conducting Sphere)

Outside the shell: E = (1/4πε0) Q / r^2; Inside the shell: E = 0.

Uniform Electric Field

A field with constant magnitude and direction throughout the region; field lines are straight, parallel, and evenly spaced.

Flux through a Cube Face (Central Charge)

If a charge q is at the center of a cube, the flux through any one face is q/(6ε0).

Electric Field due to a Point Charge

E at distance r from a point charge q is E = k q / r^2; directed radially away from a positive charge.

Coulomb's Constant (k)

k = 1/(4π ε0) ≈ 9×10^9 N m^2/C^2.

Vacuum Permittivity (ε0)

Permittivity of free space, ε0 ≈ 8.85×10^-12 F/m; appears in Coulomb's and Gauss's laws.

Charge Density ( Linear, Surface, Volume )

Linear density λ = Q/L; surface density σ = Q/A; volume density ρ = Q/V.

Flux Through Uniform Field at an Angle

Φ_E = E A cos θ; for a plane area A at angle θ to the field.