Typical data for dry soil are given below for different frequencies. By calculating

values for the penetration depth, obtain a first$-$order answer to each of the following

questions:

$($a$)$ Can a $30-$KHz antenna radiate effectively into air if it is buried $5$ m deep in the

ground? $($

$2\mathrm{.}8,4$x$10$ mho $/$ m$,$

r $1$

$4$

r

$===$

$$

$$

$)$

$($b$)$ Can a $10-$GHz ground penetrating radar be used to look for metal ores at a depth

of $20$ m$?($

$2\mathrm{.}5,8$x$10$ mho $/$ m$,$

r $1$

$3$

r

$===$

$$

$$

$)$

$($c$)$ Is an earthworm much safer from exposure to electromagnetic radiation if it

detours a few meters underground when passing a $60-$Hz power line?

$($

$2\mathrm{.}9,6$ x$10$ mho $/$ m$,$

r $1$

$5$

r

$===$

$$

$$

$)$