4. (20 pts) A uniform plane wave is traveling in seawater. Assume that the x - y plane resides

just below the sea surface and the wave travels in the +z-direction into the water. The

constitutive parameters of seawater are € = 80 and o=4 S/m. If the magnetic field at z = 0

is

H(0, t) = 90.1 cos(2π x 10³t+15)

a) Obtain expressions for Ē(z, t) and H(z, t).

b) Determine the depth at which the magnitude of E is 1% of its value at z = 0.