- Meissner Effect Definition: The Meissner effect is defined as the expulsion of magnetic fields from a superconductor when it is cooled below its critical temperature.
- Discovery and Experiment: German physicists Walther Meissner and Robert Ochsenfeld discovered the Meissner effect in 1933 through experiments with tin and lead samples.
- Meissner State: The Meissner state occurs when a superconductor expels external magnetic fields, creating a state with zero magnetic field inside.
- Critical Magnetic Field: A superconductor returns to its normal state if the magnetic field exceeds the critical magnetic field, which varies with temperature.
- Application of Meissner Effect: The application of the Meissner effect in magnetic levitation is crucial for high-speed bullet trains, allowing them to float above tracks and reduce friction.
When Superconductors are cooled below their critical temperature, they expel magnetic field and prevent them from entering. This phenomenon is called the Meissner effect, discovered by German physicists Walther Meissner and Robert Ochsenfeld in 1933. They observed that cooling tin and lead samples below the critical temperature in an external magnetic field increased the magnetic field outside the samples, showing that the superconductors expelled the internal magnetic field.
Meissner State
This state of the superconductor is called the Meissner state. An example of the Meissner effect is shown in the figure below.
The Meissner state breaks when the magnetic field—either external or produced by the current in the superconductor—exceeds a certain value, causing the superconductor to behave like an ordinary conductor.
This specific magnetic field value, beyond which a superconductor returns to its normal state, is called the Critical Magnetic Field. Its value depends on temperature, increasing as the temperature drops below the critical temperature. The figure below shows how the critical magnetic field varies with temperature.
Application of Meissner Effect
The Meissner effect is used in magnetic levitation, which powers modern high-speed bullet trains. In the superconducting state, the expulsion of the external magnetic field causes the superconducting material to levitate above a magnet or vice-versa. This principle enables bullet trains to float above the tracks, reducing friction and allowing high speeds.
