Skin effect

Question

Skin effect

Examoogle · Accepted Answer

Option C: Increases effective resistance but reduces internal reactance

Explanation & Concepts:
Skin effect is the tendency of alternating current (AC) to concentrate near the surface of a conductor rather than being distributed uniformly throughout its cross-section. This reduced effective cross-sectional area leads to an increase in AC resistance, while the reduced internal flux linkage inside the conductor results in a decrease in internal reactance.

Working Principle: The phenomenon occurs due to eddy currents induced by the internal magnetic field of the conductor. As AC frequency increases, these eddy currents oppose the current flow at the center of the wire, forcing the majority of the current to flow through a thinner outer 'skin' layer. Since effective cross-sectional area $A_{eff}

Key Formulas: $R_{AC} = R_{DC} \cdot k$; $X_{int} = \frac{\omega \mu_0}{8\pi}$

Key Points: Skin effect is dependent on frequency, conductor diameter, and permeability.; It is negligible at DC (f = 0).; Stranded conductors are often used to mitigate this effect.; The depth of penetration is denoted by the skin depth δ, where $\delta = \sqrt{\frac{2\rho}{\omega\mu}}$.

Advantages: Used in surface hardening of metals (induction heating).; Protects internal components from external electromagnetic interference.

Disadvantages: Increased power losses in power transmission lines.; Reduction in the current-carrying capacity of large conductors.

Applications: Power system transmission lines.; High-frequency communication cables.; Induction heating systems.

Additional Info: Skin effect increases with higher frequencies, making it critical in RF and high-voltage transmission lines.. Option A is incorrect as internal reactance decreases, not increases.. Option D is incorrect as it reverses the physical behavior of both resistance and reactance.

Answer: C is correct — Skin effect forces the current towards the surface, increasing the effective resistance due to reduced cross-sectional area while decreasing internal reactance due to diminished flux linkage in the conductor's core.

Exam Tip: Remember that Skin Effect is proportional to the square root of frequency; therefore, it is far more significant in 50Hz/60Hz power lines compared to DC, and significantly worse at radio frequencies (MHz/GHz).

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Option A: Increases the effective resistance and internal reactance

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Option B: Reduces effective resistance and internal reactance

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Option D: Reduces effective resistance but increases internal reactance

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