Here's why:
* Skin Effect: AC current does tend to concentrate near the surface of a conductor, especially at higher frequencies. This phenomenon is known as the "skin effect." The deeper you go into the conductor, the weaker the current becomes.
* Reason for Skin Effect: The changing magnetic field created by the AC current induces eddy currents within the conductor. These eddy currents oppose the main current flow, effectively pushing it towards the surface. The higher the frequency, the stronger the induced magnetic field and the more pronounced the skin effect.
* Not Just the Surface: While AC current is strongest at the surface, it does still flow throughout the entire conductor, just not with equal intensity.
* DC Current: DC current, on the other hand, flows uniformly throughout the conductor's cross-section. There is no skin effect with DC.
Practical Implications:
* Transmission Lines: In high-voltage AC transmission lines, the skin effect is significant. To minimize losses, conductors are often hollow or made of stranded wires to increase the surface area available for current flow.
* High-Frequency Applications: In circuits operating at very high frequencies (e.g., radio waves), the skin effect is very pronounced. This can affect the performance of antennas and other components.
In conclusion:
The skin effect causes AC current to concentrate near the surface of a conductor, but it does not flow exclusively on the surface. The deeper you go into the conductor, the weaker the current becomes. The extent of the skin effect depends on the frequency of the AC current.
