Aplane monochromatic radio wave (λ = 0.4 m) travels in vacuum along the positive x-axis, with a time-averaged intensity i = 25 w/m2. suppose at time t = 0, the electric field at the origin is measured to be directed along the positive y-axis with a magnitude equal to its maximum value. what is bz, the magnetic field at the origin, at time t = 2 ns? bz =