Superconductivity: The Meissner Effect, Persistent Currents and the Josephson Effects

Several phenomena associated with superconductivity are observed in three experiments carried out in a liquid helium cryostat. The transition to the superconducting state of several bulk samples of Type I and II superconductors is observed in measurements of the exclusion of magnetic field (the Meisner effect) as the temperature is gradually reduced by the flow of cold gas from boiling helium. The persistence of a current induced in a superconducting cylinder of lead is demonstrated by measurements of its magnetic field over a period of a day. The tunneling of Cooper pairs through an insulating junction between two superconductors (the DC Josephson effect) is demonstrated, and the magnitude of the fluxoid is measured by observation of the effect of a magnetic field on the Josephson current.