Electric Charges, Forces, and Fields

Vocabulary flashcards covering electric charges, forces, Coulomb's Law, conductors, insulators, polarization, electric fields, and dipole configurations from Physics lecture notes.

Neutrally Charged Object

An object that contains an equal number of positive ($+$) and negative ($-$) charges, resulting in zero net charge.

Rubber Charge Behavior

The property of rubber to acquire a negative electric charge when rubbed against materials like hair or felt.

Glass Charge Behavior

The property of glass to acquire a positive electric charge when rubbed.

Neutral Lithium Atom (Li)

An atom composed of $3$ protons ($3+$), $4$ neutrons, and $3$ electrons ($3-$), where equal numbers of electrons and protons produce zero net charge.

Polarization

The process where electrons in each molecule of a neutral insulator shift away from a charged object (such as a negatively charged comb), bringing positive charges closer and generating a net attractive force.

Electrical Conductor

A material inside which it is easy for electric charges to move freely.

Electrical Insulator

A material inside which electric charges do not move much and are treated as fixed.

Semiconductor

A material that behaves like an electrical insulator until sufficient energy is supplied to cross its energy gap, enabling charges to move.

Coulomb's Law

The law stating that the magnitude of the electric force between two point charges is directly proportional to the product of their charges and inversely proportional to the square of the distance between them: $F = \frac{k q_1 q_2}{r^2} = \frac{q_1 q_2}{4\pi\varepsilon_0 r^2}$.

Electrostatic Constant ($k$)

The constant in Coulomb's Law, equal to $k = 8.99 \times 10^9\,N\,m^2/C^2$, or $k = \frac{1}{4\pi\varepsilon_0}$.

Permittivity of Free Space ($\varepsilon_0$)

A constant defined as $\varepsilon_0 = 8.85 \times 10^{-12}\,C^2/N\,m^2$, related to the electrostatic constant by $k = \frac{1}{4\pi\varepsilon_0}$.

Electric Field ($\mathbf{E}$)

A field created by electric charge that exerts a force per unit charge on a test charge $q_0$, defined as $\mathbf{E} = \frac{\mathbf{F}}{q_0}$.

Electric Field of a Point Charge

The field generated by a point charge $q$ at distance $r$, given by $\mathbf{E} = \frac{k q}{r^2} \hat{r} = \frac{1}{4\pi\varepsilon_0} \frac{q}{r^2} \hat{r}$, pointing away from positive charges and toward negative charges.

Superposition of Electric Fields

The principle stating that the total electric field at a point is the vector sum of the electric fields produced by each charge present: $\mathbf{E}_{tot} = \sum \frac{k q_i}{r_i^2} \hat{r}_i$.

Electric Dipole

A system formed by two equal and opposite charges ($+q$ and $-q$) separated by a distance (such as $2a$).

Surface Charge Density ($\sigma$)

The measure of electric charge per unit area, expressed as $\sigma = \frac{Q}{A}$ with SI units of $\text{C/m}^2$.

Charge Behavior on Conductors

Principles stating that all excess charges move to the outer surface of a conductor spaced uniformly, the electric field inside a conductor is zero, and the electric field just outside is perpendicular to the surface with magnitude $E = \frac{\sigma}{\varepsilon_0}$.