Magnetic Field that Destroys Superconductivity: Critical Field

The correct answer to the question is option 'D', the critical field. Let's explore in detail why the critical field is the magnetic field that destroys superconductivity.

What is Superconductivity?
Superconductivity is a phenomenon where certain materials exhibit zero electrical resistance when cooled below a critical temperature. In superconducting materials, the electric current can flow indefinitely without any energy loss. This property is highly desirable for various applications, such as power transmission, magnetic levitation, and high-speed electronics.

The Meissner Effect
One of the unique characteristics of superconductors is the expulsion of magnetic fields from their interior. When a superconductor is subjected to an external magnetic field, it generates an opposing magnetic field within itself, resulting in the expulsion of the applied magnetic field. This phenomenon is known as the Meissner effect.

The Critical Field
The critical field is the maximum magnetic field strength that a superconductor can withstand before it loses its superconducting properties. It represents the threshold beyond which the Meissner effect fails to expel the magnetic field, and the superconductor transitions into a normal conducting state with non-zero resistance.

Types of Magnetic Fields
Let's briefly discuss the different types of magnetic fields mentioned in the options:

1. Diamagnetic Field: A diamagnetic material generates an induced magnetic field in the opposite direction to an applied magnetic field. However, diamagnetic materials do not destroy superconductivity. In fact, superconductors exhibit strong diamagnetic properties.

2. Ferromagnetic Field: Ferromagnetic materials exhibit spontaneous magnetization, but they do not destroy superconductivity. Superconductors can coexist with ferromagnetic materials in certain cases, leading to interesting phenomena like the proximity effect.

3. Ferrimagnetic Field: Ferrimagnetic materials have a complex magnetic structure with both ferromagnetic and antiferromagnetic properties. However, they are not directly related to the destruction of superconductivity.

The Critical Field and Superconductivity
The critical field depends on various factors, including the type of superconductor, temperature, and material properties. It represents the limit beyond which the superconductor can no longer maintain the Meissner effect, and the magnetic field begins to penetrate the material. This penetration leads to the creation of magnetic vortices and the subsequent increase in resistance, resulting in the loss of superconductivity.

In summary, the magnetic field that destroys superconductivity is known as the critical field. It represents the maximum magnetic field strength that a superconductor can withstand before transitioning into a normal conducting state. The critical field is influenced by various factors and represents the threshold beyond which the Meissner effect fails to expel the magnetic field.