What phenomenon restricts the current-carrying area at the center conductor of a coaxial line?

The skin effect is the phenomenon that restricts the current-carrying area to the outer surface of the conductor in a coaxial line as the frequency of the current increases. In essence, when alternating current (AC) flows through a conductor, it doesn't penetrate uniformly throughout the material but rather travels along the surface, which leads to a decrease in the effective cross-sectional area available for conduction. This effect becomes more pronounced at higher frequencies, causing most of the current to flow near the surface of the conductor and making it seem as though the usable area for carrying current is limited to a "skin" layer.

Understanding the skin effect is essential for designing and analyzing systems that operate at high frequencies, as it significantly impacts resistance, signal loss, and efficiency in coaxial cables and other transmission lines. It is crucial to recognize that this effect is tied to the inherent properties of AC conductivity in conductors, not influenced by concepts such as capacitance, inductive reactance, or any dielectric properties, which focus on different aspects of electrical behavior and signal propagation.