Carnot efficiency η = 1 - T₂/T₁, depending solely on absolute temperatures of heat source (T₁) and sink (T₂). It is independent of working substance, engine size, or other details. This universality makes Carnot cycle the theoretical maximum efficiency benchmark. Memory tip: 'Carnot efficiency: only T_hot and T_cold matter; real engines have lower efficiency'. This thermodynamics concept is frequently tested in competitive exams. Always recall that Carnot efficiency is an ideal limit; real engines have additional losses reducing efficiency below this value.
Explanation:
Superconductivity occurs in certain materials below a critical temperature T_c, where electrical resistance drops abruptly to zero, and magnetic fields are expelled (Meissner effect). Option B describes insulators; C and D are unrelated. Memory aid: 'Superconductor: R=0 below T_c; perfect diamagnetism'. This modern physics concept is frequently tested in competitive exams. Always distinguish superconductivity (zero resistance) from perfect conductivity (theoretical limit); real superconductors exhibit Meissner effect, a defining property.
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