### Key Terms

- ampere (amp)
- SI unit for current; $1\phantom{\rule{0.2em}{0ex}}\text{A}=1\phantom{\rule{0.2em}{0ex}}\text{C/s}$

- 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
- $(\phantom{\rule{0.2em}{0ex}}\text{\Omega}\phantom{\rule{0.2em}{0ex}})$ unit of electrical resistance, $1\phantom{\rule{0.2em}{0ex}}\text{\Omega}\phantom{\rule{0.2em}{0ex}}=1\phantom{\rule{0.2em}{0ex}}\text{V/A}$

- 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 $\left({T}_{C}\right)$