Question

The phenomenon where a superconductor expels an external magnetic field is known as:

• A. BCS effect
• B. Meissner effect
• C. Josephson effect
• D. Hall effect

Hint:

Superconductors don’t let magnetic fields in — they push them out! That’s the Meissner effect, a signature of true superconductivity.

Answer 1

The Correct Option is B

Superconductors are special materials that exhibit zero electrical resistance below a certain critical temperature. One of the key defining phenomena of superconductivity is the Meissner effect.
What is the Meissner Effect?

• When a material transitions into the superconducting state, it not only loses all electrical resistance but also actively expels magnetic fields from its interior.
• This means the magnetic field lines are pushed out, making the magnetic flux inside the superconductor exactly zero — a property that distinguishes superconductors from perfect conductors.
• This effect leads to magnetic levitation and is used in applications like maglev trains.

Why the Other Options Are Incorrect:

• (A) BCS Effect: Refers to Bardeen-Cooper-Schrieffer theory, which explains the microscopic mechanism of superconductivity, not magnetic field expulsion.
• (C) Josephson Effect: Describes tunneling of superconducting electron pairs through an insulating barrier — not related to magnetic field behavior.
• (D) Hall Effect: Occurs in semiconductors and conductors where a magnetic field causes charge carriers to deflect — unrelated to superconductivity.

Thus, the correct answer is the Meissner effect, which defines the unique magnetic behavior of superconductors.