Charge and Current Practice Flashcards

Flashcards covering the fundamentals of electric charge, current, Kirchhoff's laws, and the properties of materials as conductors or insulators based on their number density and mean drift velocity.

Electric Current ($I$)

The rate of flow of charge, defined by the equation $I = \frac{\Delta Q}{\Delta t}$ where current is measured in amperes ($A$).

Coulomb ($C$)

The SI derived unit of electric charge, equivalent to one ampere-second ($1\,A\,s$). It is the charge flowing past a point in one second when the current is one ampere.

Elementary Charge ($e$)

The charge on a single proton, equal to $1.60 \times 10^{-19}\,C$. The charge on an electron is $-1.60 \times 10^{-19}\,C$.

Quantisation of Charge

The principle that the net charge on a particle or object can only take values that are integer multiples of the elementary charge ($e$).

Charge Carrier

Any particle that has an electric charge, such as protons, electrons, or ions, whose movement constitutes an electric current.

Net Charge ($Q$)

The total charge on an object, resulting from a gain or loss of electrons, calculated by the equation $Q = \pm ne$ where $n$ is an integer.

Conduction Electrons

Free electrons in a metal that are not fixed to specific atoms and are free to move through the crystal lattice, also known as delocalised electrons.

Conventional Current

A model of current direction treated as flowing from the positive terminal to the negative terminal.

Electron Flow

The actual movement of electrons in a metal wire, which travel from the negative terminal towards the positive terminal, opposite to conventional current.

Electrolytes

Liquids that can carry an electric current as a flow of ions; these are typically molten ionic compounds or ionic solutions like salt dissolved in water.

Anions and Cations

In an electrolyte, anions are negatively charged ions stimulated toward the positive anode, while cations are positively charged ions stimulated toward the negative cathode.

Ammeter

An instrument used to measure electric current, placed in series in a circuit; an ideal ammeter has zero resistance.

Kirchhoff's First Law

A law based on the conservation of charge stating that for any point in a circuit, the sum of currents entering that point equals the sum of currents leaving ($\Sigma I_{in} = \Sigma I_{out}$).

Conservation of Charge

A fundamental physical law stating that electric charge can neither be created nor destroyed; the total amount of charge in the universe is constant.

Number Density ($n$)

The number of free charge carriers per cubic metre of a material ($m^{-3}$), used to determine how well a material conducts electricity.

Conductor

A material with a very high number density of free electrons, typically on the order of $10^{28}\,m^{-3}$.

Semiconductor

A material with a number density between that of conductors and insulators, approximately $10^{17}\,m^{-3}$, where electrons must move faster to carry the same current as a metal.

Insulator

A material with a very low number density of free charge carriers, making it a poor conductor of electricity.

Mean Drift Velocity ($v$)

The average velocity of charge carriers as they travel through a conductor, taking into account random collisions with fixed positive ions.

Drift Velocity Equation ($I = Anev$)

The equation relating current ($I$) to cross-sectional area ($A$), number density ($n$), elementary charge ($e$), and mean drift velocity ($v$).

Millikan's Oil-Drop Experiment

A 1909 experiment that determined the charge on oil droplets was quantised and allowed the calculation of the elementary charge ($e$) as $-1.59 \times 10^{-19}\,C$.