Facts About Superconductors – Select the Correct Set Consider the statements about superconductors: B = 0 inside (perfect diamagnetic expulsion – Meissner effect). μr is high. Diamagnetism is very high (perfect). Transition temperature varies with isotopic mass (isotope effect). Which combination of statements is correct?

Introduction / Context:
Superconductivity is defined by zero DC resistance and perfect diamagnetism (Meissner effect). Several concise statements are given; the task is to identify which are accurate and consistent with superconducting physics near and below the critical temperature.

Given Data / Assumptions:

• Type I/II superconductors in the Meissner state (below Hc or Hc1).
• Static or low-frequency fields (no flux penetration in the Meissner state).
• Conventional superconductors showing the isotope effect.

Concept / Approach:

(1) True: The Meissner effect expels magnetic flux so B ≈ 0 in the bulk (away from a thin penetration depth). (2) False: Superconductors exhibit μr ≈ 0 (effective relative permeability near zero due to perfect diamagnetism), not “high”. (3) True: “Very high diamagnetism” is another way of stating the Meissner effect. (4) True: The transition temperature Tc shows an isotope effect in conventional superconductors, supporting phonon-mediated pairing (BCS theory), i.e., Tc ∝ M^−α for some α around 0.5 in simple cases.

Step-by-Step Solution:

Verification / Alternative check:

Measurements show magnetic susceptibility χ ≈ −1, corresponding to μr ≈ 0; isotope effect historically observed in Hg and others confirms statement 4.

Why Other Options Are Wrong:

• Any option including statement 2 is incorrect because μr is not high in superconductors.
• Options omitting either 1 or 3 miss the Meissner effect.

Common Pitfalls:

Confusing high permeability (ferromagnets) with perfect diamagnetism (superconductors); forgetting the nuance of penetration depth and mixed state in type II above Hc1.

Final Answer:

1, 3, and 4 are correct