We observed that whenever the frequency of an AC circuit was increased, the voltage across an RC component changed shape. Specifically, 1) the trace lost its exponential growth and decay and instead had linear growth and decay, and 2) the voltage amplitude was much smaller. My guess as to the reason this occurs is because an increase in the frequency means that the voltage, and therefore current, in the circuit changes directions more rapidly. Therefore, the current does not travel long enough in a certain direction to allow the capacitor to build up charge. This would explain the smaller amplitude part. I'm also guessing this is the reason it appears linear. Since it is not given enough time to build, you are only seeing the very beginning segment of an exponential growth and decay trace, which appears linear when this time interval is small enough. That is, even a sine wave would look linear if you took a small enough segment. I don't have the background to answer this question with concrete math formulas (well, I might, but I can't recall them), so I hope this more verbose answer still works. Thanks.