4) An infinite wire carrying a constant current I in the positive z-direction is moving with constant velocity voy rigidly. Calculate the induced electric field E at the instant the wire coincides with the z-axis using the quasi-static approximation (that is assuming that the formula for the vector potential for steady currents work while the wire is moving). Hint: Pretend that the wire is of very large but finite length, so restrict it to -L < z < L, compute the vector potential, evaluate E in the quasi-static approximation and then take the limit as L.