The GATE Grind

GATE 2018 EC – Question 43

Electromagnetics · Plane Waves and Properties · 2 marks · Multiple choice

The distance (in meters) a wave has to propagate in a medium having a skin depth of 0.1 m so that the amplitude of the wave attenuates by 20 dB, is

  1. 0.12
  2. 0.23
  3. 0.46
  4. 2.3

Practise this question in The GATE Grind →

Show answer and explanation

Correct answer: (B) 0.23

Explanation

The amplitude falls as $e^{-x/\delta}$. A 20 dB attenuation is a factor of 10, so $e^{-x/\delta}=0.1$ and $x=\delta\ln10=0.1\times2.303=0.23$ m.