In a typical oscillator circuit, the current is 90deg out of phase with the applied voltage. Since the magnetic field is proportional to current, it too would be 90deg out of phase with the applied voltage. Reducing the oscillator to molecular size, you would have electrons going in and out of a tiny antenna. The potential of the antenna would be max or min when the current is zero. So my intuition tells me the textbook is correct.
I think it was Plank who said, in so many words, that a photon is either a wave or a particle, depending on which you are looking for. Look for a wave and you'll find a wave; look for a particle and you'll find a particle. The two-slit experiment works for waves or particles. For particles, it is a probability distribution; for waves it is an interference pattern.
The laser clock is ideal for understanding how time is relative to velocity. The light reflects back and forth between the ends of the laser, emitting one pulse of light each time it arrives at a particular end (not at both ends). To a first observer, moving with the clock, it takes the same amount of time for light to go from end to end in either direction. To a second observer, watching the clock pass at high speed, the light takes longer to go from back to front than from front to back. The total distance traveled by the light during one clock pulse is twice the length of the laser plus the distance it travelled during one pulse. Therefore, the clock runs slower in the second observer's reference frame.
Of course, actually seeing the clock pulses is another matter; you have to add the time it takes for light to travel from the clock to the observer, which brings in the doppler shift. So the second observer will see the clock running faster as it approaches and slower as it goes away; but correcting for the doppler shift will reveal that the clock is running at the same slow rate the whole time.
