---
title: "Normal conductor versus superconductor"
subject: "Electrical Engineering Material"
chapter: 5
key: "semester_3/electrical_engineering_material:normal-vs-superconductor"
source: https://www.bctengineer.com/q/semester_3/electrical_engineering_material/normal-vs-superconductor
site: BCT Engineering
---

# Normal conductor versus superconductor

Electrical Engineering Material · Chapter 5: Superconductivity

- Asked in: 2078 Kartik, 4 marks
- Video: [What is a Superconductor? | How it's different from a regular conductor? |Superconductivity](https://www.youtube.com/watch?v=__WQeHrEz28) — NO MORE ratta maar
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_3/electrical_engineering_material/normal-vs-superconductor
- Whole chapter: https://www.bctengineer.com/md/semester_3/electrical_engineering_material/chapter-5

## Question

Differentiate between a normal conductor and a 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.

## Answer

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) |

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

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. How does resistance differ?
   A. Normal conductor falls gradually and keeps residual R; superconductor drops suddenly to exactly zero at Tc
   B. Both fall suddenly to zero at the same temperature
   C. Normal conductor reaches zero at 0 K, superconductor stays constant
   D. Superconductor has finite resistance, normal conductor zero
   Answer: A. A superconductor has a sharp transition at Tc to R = 0. (Key point: Resistance behaviour)

2. How does a superconductor respond to a magnetic field?
   A. The field passes through, B = mu0 H
   B. It expels the field: B = 0 and susceptibility = -1
   C. It amplifies the field
   D. It becomes paramagnetic
   Answer: B. A normal conductor lets the field through; a superconductor is a perfect diamagnet. (Key point: Magnetic behaviour)

3. What carries current in a superconductor?
   A. Single free electrons
   B. Holes only
   C. Cooper pairs
   D. Ions
   Answer: C. Normal conductors use single free electrons; superconductors use Cooper pairs. (Key point: Carriers)

4. What happens to current in a closed superconducting loop?
   A. It decays quickly through I^2R loss
   B. It doubles each cycle
   C. It is blocked by the Meissner effect
   D. It persists indefinitely
   Answer: D. Zero resistance means no decay of the current. (Key point: Current in a loop)

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- [Direct versus indirect band gap semiconductors](https://www.bctengineer.com/question.md?key=semester_3%2Felectrical_engineering_material%3Adirect-indirect-bandgap) — Electrical Engineering Material, chapter 6

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