AP Physics C E&M: Current and Resistance

ampere, A

SI unit for current; 1 A = 1 C/s

circuit

complete path that an electrical current travels along

conventional current

current that flows through a circuit from the positive terminal of a battery through the circuit to the negative terminal of the battery

critical temperature

temperature at which a material reaches superconductivity

current density, J

flow of charge through a cross-sectional area divided by the area

diode

nonohmic circuit device that allows current flow in only one direction

drift velocity, v

velocity of a charge as it moves nearly randomly through a conductor, experiencing multiple collisions, averaged over a length of a conductor, whose magnitude is the length of conductor traveled divided by the time it takes for the charges to travel the length

electrical conductivity, σ

measure of a material's ability to conduct or transmit electricity

electrical current, I

rate at which charge flows

electrical power, P

time rate of change of energy in an electric circuit

nonohmic

type of a material for which Ohm's law is not valid

ohm, Ω

unit of electrical resistance, 1 Ω = 1 V/A

ohmic

type of a material for which Ohm's law is valid, that is, the voltage drop across the device is equal to the current times the resistance

Ohm's law

empirical relation stating that the current I is proportional to the potential difference ΔV; it is often written as ΔV = IR , where R is the resistance

resistance, R

electric property that impedes current; for ohmic materials, it is the ratio of voltage to current, R = ΔV/I

resistivity, ρ

intrinsic property of a material, independent of its shape or size, directly proportional to the resistance

schematic

graphical representation of a circuit using standardized symbols for components and solid lines for the wire connecting the components

superconductivity

phenomenon that occurs in some materials where the resistance goes to exactly zero and all magnetic fields are expelled, which occurs dramatically at some low critical temperature

drift velocity

In a wire, charges lose kinetic energy to the material, reaching a constant velocity known as "___________."

positive, negative

In a schematic, the longer line represents the ___________ terminal of a battery, and the shorter line represents the ___________ terminal.

positive, electrons

Even though conventional current points in the direction ___________ charges would flow, the actual current is ___________ flowing in the opposite direction.

potential difference

Unlike conductors in electrostatic equiibrium, charges in a circuit are prevented from ever reaching equilibrium due to an external source of ___________.

electric field

An ___________ is present in a conductor when there is a current flowing within.

kinetic

Work done on charges by electric field does not increase ___________ energy; the work only maintains their "drift velocity." Free-electron collisions transfer energy to atoms of the conductor.

free electrons

Electrons far enough away from nuclei to not experience much attraction. They are part of the "sea of electrons" that flow in a current.

vector

Current density is a ___________ quantity. It points in the direction of net flow of positive charges through an area.

density

Current ___________ is used to show relationship between current and potential difference.

temperature coefficient, α

How much a material's resistivity varies with temperature.

shape, properties, temperature

Resistance of an object is determined by the ___________ of the object, the ___________ of the object's material, and its ___________.