Meissner Effect Quiz

Meissner Effect

• The Meissner effect is the expulsion of magnetic fields from a superconductor during its transition to a superconducting state.
• The Meissner effect was discovered by Walther Meissner and Robert Ochsenfeld in 1933.

Effects on Magnetic Fields

• When the Meissner effect occurs, a nearby magnet will be repelled.
• The interior magnetic fields of superconducting tin and lead samples are expelled during the Meissner effect.

Equilibrium and Expulsion

• The equilibrium state that determines the ability for the expulsion effect in a superconductor is thermodynamic equilibrium.
• The Meissner state breaks down when the strength of the applied field rises above a critical value.

Type-I and Type-II Superconductors

• In type-I superconductors, when the strength of the applied field rises above a critical value, the Meissner state breaks down.
• In type-II superconductors, when the applied field rises above a second critical field strength Hc2, the Meissner state breaks down.
• The motion of flux vortices induced by the Lorentz forces from the current in some type-II superconductors is called flux flow.

London Equation

• The London equation predicts that the magnetic field in a superconductor will decay exponentially with distance from the surface.
• In a weak applied field, a superconductor expels nearly all magnetic flux.
• The manifestation of the phase transition from conductor to superconductor is the exclusion of magnetic fields.

Intermediate State

• Type-I superconductors exhibit an intermediate state consisting of a baroque pattern of regions of normal material mixed with regions of superconducting material.

Magnetic Flux Expulsion

• A weak applied field induces perfect diamagnetism near the surface of a superconductor, expelling magnetic flux.
• According to the London equation, the magnetic field energy is minimized in a superconductor.