How do superconductors differ from normal conductors in terms of resistance?

Superconductors differ from normal conductors as they have zero electrical resistance when cooled below a certain temperature.

Superconductors are materials that can conduct electricity without any resistance. This is in stark contrast to normal conductors, such as copper or silver, which always have some level of resistance, no matter how low the temperature. The phenomenon of superconductivity was first discovered in 1911 by Heike Kamerlingh Onnes, who found that mercury, when cooled to very low temperatures, could conduct electricity without resistance.

The key difference between superconductors and normal conductors lies in their behaviour at low temperatures. Normal conductors, as they cool down, will show a decrease in electrical resistance. However, this resistance never reaches zero. On the other hand, superconductors exhibit a sudden transition to zero resistance when they are cooled below a certain critical temperature. This critical temperature varies for different materials.

The reason for this zero resistance in superconductors is due to the formation of Cooper pairs. In a normal conductor, individual electrons move through the lattice structure of the material, often colliding with atoms and other electrons, which creates resistance. However, in a superconductor below its critical temperature, electrons pair up to form Cooper pairs. These pairs move through the lattice without any collisions, resulting in zero resistance.

This property of superconductors makes them extremely useful for a variety of applications. For instance, they are used in MRI machines, particle accelerators, and power lines, where the absence of electrical resistance allows for more efficient transmission of electricity. However, the need to cool superconductors to very low temperatures currently limits their practical use.

In summary, while normal conductors always exhibit some level of resistance, superconductors can achieve zero electrical resistance when cooled below a certain temperature, making them unique in the world of physics.