**Category:** Electromagnetism  
**Subtype:** AC Circuits (Alternating Current Circuits)  
**Problem Description:** This problem involves the phase relationship between voltage and current in a circuit that contains only a capacitor. The task is to determine how the voltage across the capacitor relates to the current flowing through it in terms of phase difference.  

**Key Concepts:**  
- In a purely capacitive AC circuit, the voltage lags behind the current.  
- The phase difference is typically \(\frac{\pi}{2}\) (or 90 degrees), meaning the voltage reaches its maximum value a quarter cycle after the current does.  

**Answer Options:**  
A. Voltage lags by \(\frac{\pi}{4}\)  
B. Voltage lags by \(\frac{\pi}{2}\)  
C. Voltage leads by \(\frac{\pi}{2}\)  
D. Voltage leads by \(\frac{\pi}{4}\)  

**Correct Answer:** B. Voltage lags by \(\frac{\pi}{2}\) compared to the current.