Halliday, Resnick & Walker — Electromagnetic Waves: Problem 65

65 A plane electromagnetic wave traveling in the positive direction of an x axis in vacuum has components $E_x = E_y = 0$ and $E_z = (4.0\text{ V/m}) \cos[(\pi \times 10^{15}\text{ s}^{-1})(t - x/c)]$. (a) What is the amplitude of the magnetic field component? (b) Parallel to which axis does the magnetic field oscillate? (c) When the electric field component is in the positive direction of the z axis at a certain point P, what is the direction of the magnetic field component there? (d) In what direction is the wave moving?