Electric Forces and Fields: Coulomb's Law, Electric Field, and Capacitors

Key vocabulary terms and definitions from the lecture notes on Coulomb's Law, electric fields, and parallel-plate capacitors.

Coulomb's Law

The electric force between two point charges is proportional to the product of the charges and inversely proportional to the square of the distance between them; magnitude F = k|q1 q2|/r^2; direction along the line joining the charges; like charges repel, opposite charges attract.

Electric charge

A property of matter that gives rise to electrical forces; charges exist as positive or negative and are measured in coulombs.

Net force (Fnet)

The resultant force on a charge due to multiple other charges; obtained by vector summing the individual forces (superposition).

Vector sum

The addition of vectors to combine magnitudes and directions; used to compute net force or net electric field.

Electric field

The region around a charge where a test charge experiences a force; defined as E = F/q; for multiple charges, the net field is the vector sum of the fields from each charge.

Uniform electric field

An electric field with the same magnitude and direction at every point between the plates of a parallel-plate capacitor.

Parallel-plate capacitor

A device with two large, flat plates carrying opposite charges; the field between plates is approximately uniform; characterized by area A, separation d, and charge Q on the plates.

Charge density (σ)

Charge per unit area on a surface, σ = Q/A; used to describe the distribution on plates of a capacitor.

Field lines

Imaginary lines that illustrate the direction of the electric field; originate on positive charges and terminate on negative charges; lines crowd where the field is strong.

Coulomb constant (k)

k ≈ 8.99×10^9 N·m^2/C^2; k = 1/(4π ε0); used in Coulomb's Law.

Like charges vs opposite charges

Like charges repel each other; opposite charges attract each other.

Electric field due to a point charge

Magnitude E = k|q|/r^2; direction is away from a positive charge and toward a negative charge.