Ohm's Law

Ohm's law states that the current through a conductor between two points is directly proportional to the potential difference across the two points. Introducing the constant of proportionality, the resistance,[1] one arrives at the usual mathematical equation that describes this relationship: I = V/R .
where I is the current through the conductor in units of amperes, V is the potential difference measured across the conductor in units of volts, and Ris the resistance of the conductor in units of ohms. More specifically, Ohm's law states that the R in this relation is constant, independent of the current.
== Tossup Questions ==
# In tokamaks, a phenomenon named for this statement has a lower power density at high temperatures and will thus be used in complement with neutral beam injection and cyclotron resonance to perform heating in ITER. One version of this statement contains a term proportional to the cross product of the current density with the magnetic field. That term is known as the Hall current. Another version of this equation states that the (*) current density is equal to the product of the conductivity and the electric field. Combining this statement with another equation for the power yields Joule's Law. For AC circuits, one quantity in this statement is replaced with the impedance. For 10 points, name this law which states that the voltage is equal to the product of current and resistance.
# It is an example of linear response theory, analogous to Fourier's law of heat transport, and thus there is a Kubo formula relating the proportionality constant in it to a two-point correlation function of electric currents. Diodes are prominent examples of materials that do not satisfy it, because they permit a flow of current in only one direction. This law can be derived from the Lorentz force with the assumption that there is a drag on charge carriers that is proportional to their velocity. Kirchoff formulated a continuum version of it equating current density to electric field times conductivity of a material. Its most familiar form states that the current through a conductor is proportional to the voltage across it and inversely proportional to resistance. For 10 points, name this law that shares its name with the SI unit of electrical impedance.