B before after ConcepTest #81 A large magnetic field points up, as shown. Initially, a proton has the z- component of its spin magnetic moment pointing up. It undergoes a spin-flip transition so that the z-component of its spin magnetic moment points down. Which of the following statements is correct? 1.A photon is absorbed during this transition. 2.A photon is emitted during this transition. 3.There is not enough information to determine if a photon is absorbed or emitted during this transition. 4.There are never any photons involved in this transition.

ConcepTest #82 Due to variations in the local environment, the protons in a certain sample experience an inhomogeneous magnetic field, as shown. At what location(s) x will the protons absorb the highest frequency electromagnetic radiation? Hold up as many cards as necessary. x B total

ConcepTest #83 A special ceramic disk is cooled below its critical temperature and becomes superconducting. A magnet is held above the superconductor, S pole down as shown below. Which of the following is correct about any currents in the superconductor? 1.As viewed from above, the currents in the superconductor are clockwise. 2.As viewed from above, the currents in the superconductor are counter- clockwise. 3.There are no currents in the superconductor.

ConcepTest #84 Which of the following changes in the quantities listed below will result in “quenching” a superconductor? a) Temperature b) Current c) External Magnetic Field