Electric Charges and Fields - Vocabulary Flashcards

Vocabulary terms and definitions covering fundamental concepts, formulas, and definitions from Chapter 1: Electric Charges and Fields.

Electrostatics

The branch of physics dealing with the study of forces, fields, and potentials arising from static (non-moving) electric charges.

Polarity of charge

The fundamental property that differentiates the two distinct kinds of electric charges (positive and negative).

Gold-leaf electroscope

A simple apparatus used to detect electric charge on a body, consisting of a vertical metal rod housed in a box with two thin gold leaves attached to its bottom end that diverge when charged.

Conductors

Substances (such as metals, human and animal bodies, and earth) that readily allow the passage of electricity through them because they contain electric charges (electrons) free to move.

Insulators

Substances (such as glass, porcelain, plastic, nylon, and wood) that offer high resistance to the passage of electricity through them and do not allow charges to move freely.

Additivity of charges

The property stating that the total charge of a system containing point charges $q_1, q_2, q_3, \text{\textellipsis}, q_n$ is obtained by adding them algebraically like real numbers ($q_{\text{total}} = q_1 + q_2 + q_3 + \text{\textellipsis} + q_n$).

Quantisation of charge

The fact that all free electric charges are integral multiples of a basic unit of charge $e$, expressed as $q = n e$ where $n$ is any positive or negative integer.

Basic unit of charge ($e$)

The magnitude of electric charge carried by an electron or a proton, equal to $e = 1.602192 \times 10^{-19}\text{ C}$.

Coulomb's Law

A quantitative law stating that the electrostatic force between two point charges is directly proportional to the product of their magnitudes, inversely proportional to the square of the distance between them, and acts along the line joining them.

Permittivity of free space ($\text{ extvarepsilon}_0$)

A constant of proportionality in Coulomb's law for vacuum, having the SI value \text{\textvarepsilon}_0 = 8.854 \times 10^{-12}\text{ C}^2\text{ N}^{-1}\text{m}^{-2}.

Principle of superposition

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

Electric field

A vector quantity defined at each point in space representing the electrostatic force experienced by a unit positive test charge placed at that point, given by $\text{\textbf{E}}(\text{\textbf{r}}) = \frac{\text{\textbf{F}}(\text{\textbf{r}})}{q}$.

Source charge

The electric charge or collection of charges that produces an electric field in the surrounding space.

Test charge

A small, ideal charge brought into an electric field to detect or measure its force without disturbing the original charge configuration of the source charge.

Electric field line

A space curve drawn such that the tangent to it at each point gives the direction of the net electric field at that point, with line density indicating field strength.

Electric flux

A scalar quantity proportional to the number of electric field lines passing through a surface element \text{\textbf{\text{\textDelta}S}}, defined as \text{\textDelta}\text{\textphi} = \text{\textbf{E}} \text{\textperiodcentered} \text{\textbf{\text{\textDelta}S}} = E \text{\textDelta}S \text{cos}(\text{\texttheta}).

Electric dipole

A system consisting of a pair of equal and opposite point charges $q$ and $-q$ separated by a fixed distance $2a$.

Electric dipole moment ($\text{ extbf{p}}$)

A vector quantity defined for an electric dipole as $\text{\textbf{p}} = q \times 2a \text{\textbf{\text{p\textasciicircum}}}$, directed from the negative charge $-q$ to the positive charge $q$.

Polar molecules

Molecules (such as $\text{H}_2\text{O}$) in which the centres of positive and negative charges do not coincide, giving them a permanent electric dipole moment even in the absence of an external electric field.

Surface charge density ($\text{ extsigma}$)

The macroscopic ratio of charge \text{\textDelta}Q to area \text{\textDelta}S on a surface element, defined as \text{\textsigma} = \frac{\text{\textDelta}Q}{\text{\textDelta}S} with SI units $\text{C}\text{ m}^{-2}$.

Linear charge density ($\text{ extlambda}$)

The macroscopic ratio of charge \text{\textDelta}Q to length \text{\textDelta}l on a line element, defined as \text{\textlambda} = \frac{\text{\textDelta}Q}{\text{\textDelta}l} with SI units $\text{C}\text{ m}^{-1}$.

Volume charge density ($\text{ extrho}$)

The macroscopic ratio of charge \text{\textDelta}Q to volume \text{\textDelta}V in a volume element, defined as \text{\textrho} = \frac{\text{\textDelta}Q}{\text{\textDelta}V} with SI units $\text{C}\text{ m}^{-3}$.

Gauss's Law

A law stating that the total electric flux through any closed surface $S$ is equal to \frac{1}{\text{\textvarepsilon}_0} times the net electric charge $q$ enclosed by $S$ (\text{\textphi} = \frac{q}{\text{\textvarepsilon}_0}).

Gaussian surface

An imaginary closed surface chosen around a charge distribution to conveniently apply Gauss's law for calculating the electric field.