How does resistance differ?

Normal conductor falls gradually and keeps residual R; superconductor drops suddenly to exactly zero at Tc

Both fall suddenly to zero at the same temperature

Normal conductor reaches zero at 0 K, superconductor stays constant

Superconductor has finite resistance, normal conductor zero

How does a superconductor respond to a magnetic field?

It expels the field: B = 0 and susceptibility = -1

The field passes through, B = mu0 H

What happens to current in a closed superconducting loop?

It decays quickly through I^2R loss

It is blocked by the Meissner effect

2078 Kartik · 4 marks

Normal conductor versus superconductor

Short answer

A normal conductor has finite resistance that decreases gradually and allows magnetic field penetration. A superconductor has exactly zero resistance below T_c and expels magnetic flux (Meissner effect, χ=−1). Current carriers are single electrons vs Cooper pairs. Superconductors have critical limits T_c, H_c, J_c; normal conductors do not.

Differentiate between a normal conductor and a superconductor.

A normal conductor (e.g. copper) always has some resistance that falls gradually with cooling, while a superconductor loses all resistance abruptly below its critical temperature $T_c$ and also expels magnetic flux.

Point	Normal conductor	Superconductor
Resistance	Finite; residual resistance remains even near 0 K	Exactly zero below $T_c$
R vs T	Falls gradually	Drops suddenly at $T_c$
Magnetic behaviour	Field passes through ( $B \approx \mu_0 H$ )	Field expelled, $B = 0$ , $\chi_m = -1$
Power loss ( $I^2R$ )	Present	Zero for DC
Current carriers	Single free electrons	Cooper pairs
Limits	No critical field or current	Limited by $T_c$ , $H_c$ , $J_c$
Current in a closed loop	Decays	Persists indefinitely
Examples	Cu, Al at room temperature	Hg (4.2 K), Nb $_3$ Sn, YBCO (92 K)

  R |        /  normal
    |      /
    |    /
    |  _/  residual R
    |  |
    |  |  superconductor
    |__|________ T
       Tc

✓ Answer checked by Claude Opus 5.5 (high effort)

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