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In its superconducting state, what is a material's DC electrical resistance?

Exactly zero, not just very small.

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  1. Very small but measurable
  2. Zero ✔
  3. It becomes an insulator

Why: Some materials lose all resistivity when cooled enough. Mercury does this below about 4.2 kelvin. A current started in a superconducting loop can keep flowing with no battery.

Huh, didn't know that: Most MRI systems use superconducting magnets because they provide strong, stable magnetic fields.

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Why are superconductors so easygoing? They offer no resistance at all.
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References

Answer: Zero. Some materials lose all resistivity when cooled enough. Mercury does this below about 4.2 kelvin. A current started in a superconducting loop can keep flowing with no battery.

  1. OpenStax College Physics 2e, 20.3 Resistance and Resistivity openstax.org/books/college-physics-2e/pages/20-3-resistance-and-resistivity
    Some even become superconductors (zero resistivity) at very low temperatures
    Checked 2026-10-10.
  2. MRI Main Field Magnets (ISMRM 2006 educational), via mri-q.com www.mri-q.com/uploads/3/4/5/7/34572113/main_field_magnets_ismrm2006.pdf
    cylindrical superconducting magnets account for more than 75% of the MRI installed base
    Checked 2026-10-11.

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