The substance which possesses zero resistance at \(0 \mathrm{~K}\) is called: (a) Super conductor (b) Insulator (c) Conductor (d) Semiconductor

Electrical resistance is a fundamental concept in the study of electricity. It is the measure of the opposition that a material presents to the flow of electric current. Think of it like a pipe with water running through it - the resistance would be any obstacle within the pipe that slows down the water flow. Similarly, electrons moving through a conductor face resistance due to collisions with the atomic structure of the material.

Resistance is usually measured in ohms (). It's determined by the material's characteristics and can be calculated using Ohm's Law, which states that the current through a conductor between two points is directly proportional to the voltage across the two points, and inversely proportional to the resistance between them. Superconductors are exceptional as they can conduct electricity without any resistance, meaning an electric current could flow indefinitely without losing energy.

Absolute zero represents the lower limit of the thermodynamic temperature scale, which is zero on the Kelvin scale, or ). At this temperature, molecules and atoms are at their lowest energy state, theoretically ceasing all motion. Although absolute zero is not achievable in practice, close approximations have been achieved in the lab, revealing extraordinary behavior of materials.

Understanding absolute zero is vital when discussing superconductivity since this phenomenon is typically observed as materials approach extremely low temperatures. The concept of absolute zero also helps us comprehend the limitations of classical thermodynamics and drives us towards quantum theory for better explanations of the behaviors at such extremes.

Critical temperature is a term used in the realm of superconductivity. It refers to the temperature below which a material becomes superconductive, displaying zero electrical resistance. Each superconductor has its own specific critical temperature, and it's only when cooled below this temperature that the superconducting properties emerge.

For instance, the critical temperature of mercury is about ), which means it begins to superconduct at that temperature when it suddenly loses all electrical resistance. Understanding this threshold is essential for the practical use of superconductors, whether it's in MRI machines, maglev trains, or quantum computers. An impressive feature of some high-temperature superconductors is their relatively high critical temperatures, requiring less extreme cooling methods, which could lead to more widespread application of superconductive technologies.