Final answer:
The Meissner effect exemplifies superconductivity by showing how superconductors expel magnetic fields and can cause magnets to levitate above them. Conductors like Cu, Ag, and Au don't become superconductors due to weak electron-lattice interactions, which prevent Cooper pairs' formation essential for superconductivity.
Step-by-step explanation:
The concept of superconductivity can be illustrated using the Meissner effect, which is a phenomenon where a superconducting material expels all magnetic field from its interior when it is below its critical temperature. In this state, materials exhibit zero electrical resistivity, allowing for current to flow without energy loss. An interesting application of this effect is the ability of a magnet to levitate above a superconductor, demonstrating the expulsion of the magnetic field.
Some materials like copper (Cu), silver (Ag), and gold (Au) do not exhibit superconductivity, likely because in these conductors the electron-lattice interaction is very weak. This weak interaction minimizes resistivity but also means that Cooper pairs, which are crucial for superconductivity according to the BCS theory, cannot form. Therefore, despite being excellent conductors at room temperature, they do not transition to a superconducting state at lower temperatures.