Electric Charges and Fields

Flashcards covering key vocabulary and concepts from the chapter on Electric Charges and Fields.

Electrostatics

Deals with the study of forces, fields, and potentials arising from static charges.

Electric Charge Discovery Credit

Given to Thales of Miletus, Greece, around 600 BC for discovering that amber rubbed with wool or silk attracts light objects.

Electrified

Bodies like glass or plastic rods, silk, fur, and pith balls said to acquire an electric charge on rubbing.

Polarity of Charge

The property that differentiates the two kinds of charges, determining whether they attract or repel.

Electrically Neutral

Said of an object when it has no electric charge.

Gold-Leaf Electroscope

A simple apparatus to detect charge on a body. Charge flows onto the leaves and they diverge, indicating the amount of charge.

Conductors

Substances that readily allow the passage of electricity through them; examples include metals, human and animal bodies, and earth.

Insulators

Substances that offer high resistance to the passage of electricity; examples include glass, porcelain, plastic, nylon, and wood.

Point Charges

Charged bodies that are very small compared to the distances between them, with all charge content assumed to be concentrated at one point in space.

Additivity of Charges

The total charge of a system is obtained simply by adding algebraically the individual charges, considering their signs.

Conservation of Charge

In an isolated system, the total charge remains constant; charges may be redistributed, but no new charges are created or destroyed.

Quantisation of Charge

All free charges are integral multiples of a basic unit of charge denoted by e; q = ne, where n is any integer.

Coulomb (C)

The SI unit of electric charge, defined in terms of electric current; one coulomb is the charge flowing through a wire in 1 second if the current is 1 ampere.

Coulomb's Law

The magnitude of the force (F) between two point charges q1, q2 separated by a distance r in a vacuum is given by F = k (q1q2)/r^2.

Permittivity of Free Space

Denoted as ε0, it appears in Coulomb’s law when written as F = 1/(4πε0) * (q1q2)/r^2; its value is approximately 8.854 × 10–12 C2 N–1m–2.

Principle of Superposition

The force on any charge due to a number of other charges is the vector sum of all the forces on that charge due to the other charges, taken one at a time.

Electric Field

The electric field produced by a charge Q at a point r is given as E(r) = (Q/4πε0) (rˆ/r^2) and specifies its value for each value of the position vector r.

Source Charge

The charge Q, which is producing the electric field.

Test Charge

The charge q, which tests the effect of a source charge.

Linear Charge Density

λ = ΔQ/Δl, where ΔQ is the charge on a small line element Δl of a wire.

Surface Charge Density

σ = ΔQ/ΔS, where ΔQ is the charge on a small area element ΔS on the surface of a conductor.

Volume Charge Density

ρ = ΔQ/ΔV, where ΔQ is the charge included in the macroscopically small volume element ΔV.

Gauss's Law

Electric flux through a closed surface S = q/ε0, where q is the total charge enclosed by S.

Gaussian Surface

Is the surface that we choose for the application of Gauss’s law.

Electric Dipole

A pair of equal and opposite point charges q and –q, separated by a distance 2a.

Dipole Moment

The dipole moment vector p of an electric dipole is defined by p = q × 2a pˆ, where pˆ is the unit vector along the dipole axis (from –q to q).

Polar Molecules

Molecules in which the centers of negative charges and of positive charges do not coincide, therefore they have a permanent electric dipole moment, even in the absence of an electric field.

Electric Flux

Electric flux through an area element S is defined by = E.S = E S cos.