This quantity’s thermally-activated “creep” is modeled in Anderson–Kim theory. A “pinched” hysteresis loop is a signature of a device whose strength is the derivative of this quantity with respect to charge. The material derivative of this quantity vanishes for infinitely conducting fluids by Alfvén’s theorem. (-5[1])The voltage produced in the AC Josephson effect (10[1])is equal to the frequency times the quantum of this quantity, which equals h over 2e. (10[1]-5[1])The “pinning” of this quantity in superconductors creates a force that allows them to levitate magnets. This quantity can be computed as the double integral of “B dot dA.” (10[1])The EMF induced in a loop is proportional to the time-derivative of this quantity, symbolized phi, by Faraday’s law. For 10 points, name this quantity that measures the density of magnetic field lines passing through a surface. ■END■ (0[2])