Key Terms

ampere (amp)

SI unit for current; $1\text{A}=1\text{C/s}$

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

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

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

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

electrical current

rate at which charge flows, $I=\frac{dQ}{dt}$

electrical power

time rate of change of energy in an electric circuit

Josephson junction

junction of two pieces of superconducting material separated by a thin layer of insulating material, which can carry a supercurrent

Meissner effect

phenomenon that occurs in a superconducting material where all magnetic fields are expelled

nonohmic

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

ohm

$(\text{Ω})$ unit of electrical resistance, $1\text{Ω}=1\text{V/A}$

Ohm’s law

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

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

resistance

electric property that impedes current; for ohmic materials, it is the ratio of voltage to current, $R=V\text{/}I$

resistivity

intrinsic property of a material, independent of its shape or size, directly proportional to the resistance, denoted by $\rho$

schematic

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

SQUID

(Superconducting Quantum Interference Device) device that is a very sensitive magnetometer, used to measure extremely subtle magnetic fields

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 $\left(T_C\right)$