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A permanent magnet is weakened by dropping it because the shock

  • A.introduces eddy currents that oppose the magnetisation
  • B.increases the reluctance of its magnetic circuit
  • C.disturbs the domain alignment
  • D.raises its temperature above the Curie point

Answer: C

Mechanical shock supplies energy that lets domains rotate into lower energy orientations, so the net moment falls. Modern rare earth magnets are far less susceptible than the older steel magnets, whose coercivity was low enough for the effect to be a practical nuisance.

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