Superconductivity
A phenomenon in which certain materials at temperatures below their critical temperature show exactly zero electrical resistance. Superconductors expel magnetic fields (Meissner effect) and carry persistent currents indefinitely without energy loss.
Real World
MRI scanners in NHS hospitals use superconducting magnets cooled to near absolute zero with liquid helium, generating powerful magnetic fields with zero energy loss — making the machines practical to run continuously.
Exam Focus
State both conditions for superconductivity: temperature below critical value AND zero resistance; missing either loses marks.
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