GATE
2018
76)
A plane electromagnetic (EM) wave traveling vertically downwards
with a frequency of 1000Hz in a homogeneous medium has a skin depth
of 100m. The ratio of the amplitude of the EM wave at a depth of 75m
with respect to the amplitude at the Earth’s surface is
______________
(Thanks to Neeraja, AU)
(Thanks to Neeraja, AU)
Solution:
A(Z) = A_o e^{-\beta Z} -----(1)
A(Z) = A_o e^{-\beta Z} -----(1)
A(Z)
– amplitude of EM at a depth Z
A_o – amplitude of EM wave at Earth’s surface(Z=0)
A_o – amplitude of EM wave at Earth’s surface(Z=0)
\beta – decay constant
Z
– depth
The
relation between the skin depth(\delta) and decay constant (\beta) is
\delta = \frac{1}{\beta}-----(2)
Skin depth, \delta = 503.8\sqrt{\frac{\rho}{f}}-----(3)
Skin depth, \delta = 503.8\sqrt{\frac{\rho}{f}}-----(3)
\beta = \frac{1}{\delta}=\frac{1}{100}=0.01
Z=75m
Substitute
in eq(1)
\frac{A_{(75)}}{A_o}= e^{-\beta Z}= e^{-0.01 \times 75} = e^{-0.75}
\frac{A_{(75)}}{A_o}= e^{-\beta Z}= e^{-0.01 \times 75} = e^{-0.75}
\frac{A_{(75)}}{A_o}=0.472
\therefore the ratio of the amplitudes= 0.472
How could you find the skin depth without knowing resistivity value
ReplyDeleteHi srinu, in the above solution skin depth is given directly, just for idea I placed the formula. Here I'm not using frequency and resistivity to calculate the skin depth.
DeletePlease read question once again, and hopefully you will understand.
thank u sir,i got it
DeleteMfoegaeQgran_po_Omaha Kimberly Turner click
ReplyDeleteclick here
link
link
adgravconse