The waveform of AC voltage across a diode shows a forward-biased condition with minimal voltage drop (ideally 0V, realistically around 0.7V) and a reverse-biased condition reflecting the full AC voltage. When a resistor is connected in series with the diode, the voltage across the resistor will vary depending on the diode's state. In forward bias, the resistor will drop voltage proportional to the current flowing through it. The overall circuit consists of an AC generator, a resistor, and a forward-biased diode in series. Understanding these waveforms is crucial for analyzing diode behavior in AC circuits.