What does it indicate when voltage and current reach their maximum value at 90 or 270 degrees?

When voltage and current reach their maximum value at 90 or 270 degrees, it indicates that they are out of phase with each other. In a purely resistive circuit, voltage and current are in phase, meaning their peaks occur at the same time, which corresponds to 0 or 180 degrees. However, when the phase difference is 90 degrees, it means that the current reaches its maximum a quarter of a cycle after the voltage does, or vice versa.

In terms of sinusoidal waveforms, a phase shift of 90 degrees means that when one waveform is at its maximum, the other is at zero, showing they are not synchronously reaching their maximum values. The phase angles given (90 degrees for lead and 270 degrees for lag) point to a scenario where the two quantities are oscillating but not reaching their peaks simultaneously. Hence, saying they are "in phase" would not apply in this context; rather, it illustrates a clear phase difference between voltage and current.