plane wave

Ei $=$y$100$ cos $($t $$ x $1\mathrm{.}73$z$)(2)$

is incident in air upon a plane soil surface at z $=0.$ The soil medium

may be assumed to be lossless dielectric with a relative permittivity

of $4.$

$($a$)$ Determine the incident angle,

$($b$)$ Obtain expressions for the total electric fields in air and in the

soil medium,