When a conductor carries more current on the surface as compared to core, it is due to

Question

Examoogle · Accepted Answer

Skin Effect

Explanation: Skin effect is the tendency of an alternating electric current (AC) to distribute itself within a conductor such that the current density is highest near the surface and decreases exponentially towards the core. This phenomenon occurs due to the opposing eddy currents induced by the changing magnetic field within the conductor.

Working Principle: When AC flows through a conductor, the internal magnetic flux linkages are greater at the center of the conductor than at the surface. This higher internal inductance at the center creates a higher reactance ($X_L = 2\pi f L$), causing the current to seek the path of least impedance, which is the surface layer. As frequency or conductor size increases, this impedance difference becomes more pronounced, forcing more current to the surface skin.

Key Formulas: $\delta = \frac{1}{\sqrt{\pi f \mu \sigma}}$ — Formula for skin depth (the distance from the surface where current density falls to $1/e$ or ~37% of its surface value).; $R_{AC} > R_{DC}$ — Relationship showing that effective resistance increases due to skin effect.

Key Points: Skin effect is negligible for DC (frequency = 0).; It increases with higher frequency ($f$), higher permeability ($\mu$), and higher conductivity ($\sigma$).; It leads to an increase in the effective resistance of the conductor.; Stranded conductors are used in transmission lines to reduce the impact of skin effect compared to solid conductors.

Advantages: In certain RF applications, it is used to save material by using hollow conductors.

Disadvantages: Increased effective resistance causes higher $I^2R$ power losses.; Reduced current-carrying capacity for a given conductor cross-section.

Applications: Power transmission lines; High-frequency radio and microwave components

Additional Info: Skin depth decreases as frequency increases; hence, copper plating is often used for high-frequency applications.. Option B (Skin Depth) is a parameter representing the phenomenon, not the phenomenon itself. Option A (Corona) refers to the electrical discharge caused by air ionization.

Answer: C is correct — The concentration of current near the surface of a conductor due to AC frequency is known as the skin effect.

Exam Tip: Remember that skin effect increases with frequency, which is why DC transmission (where $f=0$) is preferred for long-distance lines to avoid skin effect losses.

Related Questions

Discussion (0)