Find the ocean depth at which the electric field amplitude of the radio wave decreases to 1/1000 of its value at the ocean surface as well as the phase velocity, wavelength and index of refraction in the medium at each of the frequency: f_1 = KHz, f_2 = 10 KHz, f_1 = 1 KHz, f_3 = 100 KHz, f_4 = 1 MHz and f_5 = 10MHz, taking epsilon_r = 81 and sigma = 4S/m for sea water.