Which one of the following statements concerning superconductors is false? A constant current can be maintained in a superconduc
ting ring for several years without an emf. Superconductors are perfect conductors. Critical temperatures for some superconductors exceed 100 K. All materials are superconducting at temperatures near absolute zero kelvin. Below its critical temperature, the resistivity of a superconductor is zero Ω-m
