Physics 2015 JAMB Past Questions - Question 10: In an a.c. circuit that contains only a capacitor, the voltage lags behind the current by

Correct Answer

A

Explanation

In an AC circuit that contains only a capacitor, the voltage lags behind the current by a phase angle of 90 degrees. This means that the voltage waveform reaches its maximum (or minimum) 1/4 cycle, or a quarter of a period, after the current waveform reaches its maximum (or minimum).

The reason for this lag in voltage behind the current in a capacitive circuit is due to the behavior of the capacitor. A capacitor stores electrical energy in an electric field, and when the voltage across the capacitor changes, it takes some time for the capacitor to charge or discharge, which results in this phase shift.

Mathematically, you can represent the relationship between voltage (V) and current (I) in a purely capacitive circuit as:

V = I * Xc

Where:
- V is the voltage across the capacitor.
- I is the current through the capacitor.
- Xc is the capacitive reactance, which is given by Xc = 1 / (2πfC), where f is the frequency of the AC source, and C is the capacitance of the capacitor.

The phase angle between voltage and current in this relationship is 90 degrees, indicating the lag of voltage behind the current.