Which one of the following can wave propagate in a conducting medium before its amplitude becomes insignificant?

Question

Question

This question was previously asked in

UPSC ESE (Prelims) Electronics and Telecommunication Engineering 19 Feb 2023 Official Paper

Answer 1

Concept:

Skin depth is the distance over which an electromagnetic wave's amplitude decreases by a factor of 1/e (approximately 37%) as it propagates through a conductor. In other words, it is the depth at which the wave becomes "insignificant" in amplitude compared to its initial value when it first encountered the conductor.
The concept of skin depth arises due to the skin effect, which is the tendency of an alternating electric current (AC) to distribute itself within a conductor so the current density is largest near the surface of the conductor, and decreases exponentially with greater depths in the conductor. The current density is approximately zero at a depth equal to the skin depth.
As such, the skin depth is inversely proportional to the square root of the frequency of the wave: the higher the frequency, the smaller the skin depth, which means the wave becomes insignificant after propagating a shorter distance into the conductor.
The other terms listed - characteristic impedance, skip distance, and line of sight - are related to different aspects of wave propagation and do not describe the distance a wave can propagate in a conducting medium before its amplitude becomes insignificant.