AP Physics C: Electricity & Magnetism - Summer Flashcards

Vocabulary flashcards covering electric charge, materials, charging methods, current, current density, resistance, resistivity, Ohm's Law, and EMF based on AP Physics C lecture notes.

Coulomb’s Law of Electrostatic Force

Particles with the same sign of electrical charge repel each other, and particles with opposite signs attract.

Conductors

Materials through which charge moves freely, such as metals, the human body, and tap water.

Insulators (Nonconductors)

Materials through which charge cannot move freely, such as rubber, plastic, glass, and pure water.

Semiconductor

Materials with electrical properties somewhere between conductors and insulators, such as silicon and germanium.

Superconductor

A perfect conductor through which charge moves without any hindrance at all.

Grounding

The removal of excess charge on an object (discharging) by transferring charge ($e^-$) into a much bigger object.

Ground

The bigger object involved in grounding that receives or provides electrons to discharge an object.

Induced charge

Positive and negative charges in a solid state within a single object that separate due to a nearby charge.

Elementary charge ($e$)

The magnitude of charge of a proton and electron, equal to $1.602 \times 10^{-19}\,C$.

Annihilation processes

Processes in which an electron and its antiparticle (positron) transform into gamma rays ($e^- + e^+ \rightarrow \gamma + \gamma$).

Pair Production

The converse of annihilation in which a gamma ray transforms into an electron and a positron ($\gamma \rightarrow e^- + e^+$).

Triboelectric Charging (friction)

Charging resulting from rubbing objects together, moving electrons to the object with more electron affinity and causing attraction due to opposite charges.

Induction Charging (no contact)

Charging where electrons move between conductors due to a nearby charged object without direct contact.

Conduction Charging (contact)

Charging occurring through direct contact, where conductors that are connected spread charge out to eliminate excess charge.

Electric current ($i$)

A stream of moving charges existing only if there is a net flow of charges through a surface, defined as $i = \frac{dq}{dt}$.

Charge carrier

A particle free to move around that carries an electric charge, such as an electron ($e^-$).

Conventional current

Current defined as flowing from positive ($+$) to negative ($-$), drawn in the direction a positive charge carrier would flow.

Current density ($J$)

The magnitude of current per unit area of a cross-section element, given by $i = \int J\,dA$.

Drift speed ($v_d$)

The speed at which electrons drift through a conductor carrying a current, defined by $v_d = \frac{i}{nAe} = \frac{J}{ne}$.

Resistance ($R$)

The ratio of potential difference $V$ across a conductor to the current $i$ through it ($R = \frac{V}{i}$), measured in Ohms ($\Omega$).

Resistivity ($\rho$)

A material property related to electric field and current density by $\rho = \frac{1}{\sigma} = \frac{E}{J}$, measured in Ohm-meters ($\Omega\,m$).

Conductivity ($\sigma$)

The reciprocal of resistivity ($\sigma = \frac{1}{\rho}$), measured in reciprocal ohm-meters ($(\Omega\,m)^{-1}$).

Resistor

A conductor whose specific function is to provide a specific resistance in a circuit.

Ohm’s Law

The principle stating that the current through a device is directly proportional to the potential difference applied to it, provided resistance $R = \frac{V}{i}$ is independent of $V$.

Charge pump (emf device)

A device such as a battery, generator, solar cell, or fuel cell that creates and maintains a potential difference.

Electromotive force ($\varepsilon$)

The work-supplying property created by a charge pump (emf device) that maintains potential difference and drives charge flow.

Basic formula for charge

q = ne

Formula to relate current to charge

i=\frac{dq}{\differentialD t}

Formula to relate charge to current

$$q=\int_0^{t}\!i\,dt$$

Formula relating current to current density

$$i=\int JdA$$

Formula relating charge to wire properties

$$q=\left(nAL\right)e$$

Basic formula for drift speed

$$v_{d}=\frac{L}{t}$$

Formula relating current density to drift speed

$$J=\left(ne\right)v_{d}$$

Basic formula for resistance of an object

$$R=\frac{V}{i}$$

Formula relating resistance of an object to resistivity of a material

$$R=\rho\frac{L}{A}$$

Formula for magnitude of electric field

$$E=\rho J$$

Formula for resistivity based on temperature

$$\rho-\rho_0=\rho_0\alpha\left(T-T_0\right)$$

Formula for conductivity of a material

$$\sigma=\frac{1}{\rho}$$

Formula for resistivity of metals

$$\rho=\frac{m}{e^2n\tau}$$