**Understanding the Relationship between Current and Voltage in an AC Circuit**

In an AC circuit, the current through a capacitor leads the voltage across it. This fundamental concept is crucial in understanding the behavior of capacitors in alternating current circuits.

**What is an AC Circuit?**

An AC circuit is a type of electrical circuit that uses alternating current, which periodically reverses direction. AC circuits are commonly used in power distribution systems, electronic devices, and many other applications.

**Capacitor in an AC Circuit**

A capacitor is a passive component that stores energy in the form of an electric field. In an AC circuit, the capacitor is connected in series with a resistive load, such as a light bulb or a resistor.

**Leading Current**

When an AC voltage is applied across a capacitor, the current through the capacitor leads the voltage across it. This means that the current waveform reaches its maximum value before the voltage waveform reaches its maximum value.

**Why does the current lead the voltage?**

The reason for this lead is due to the nature of capacitance. Capacitance is the ability of a component to store electric charge. When a capacitor is connected to an AC source, the voltage across it changes sinusoidally. As the voltage increases, the capacitor stores energy in its electric field. As the voltage decreases, the capacitor releases energy back into the circuit.

Since the capacitor is storing energy, it takes time for the electric field to build up or collapse. This introduces a phase shift between the voltage and current waveforms, causing the current to lead the voltage.

**Phase Shift**

The phase shift between the voltage and current waveforms is 90 degrees (π/2 radians) for a pure capacitance. This means that the current waveform is shifted by 90 degrees ahead of the voltage waveform.

**Analyzing the Waveforms**

Let's analyze the waveforms of the voltage and current across a capacitor in an AC circuit:

**Voltage Waveform**
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**Current Waveform**
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As shown above, the current waveform leads the voltage waveform by 90 degrees.

**Conclusion**

In conclusion, the current through a capacitor in an AC circuit leads the voltage across it due to the nature of capacitance and the phase shift between the voltage and current waveforms. This fundamental concept is essential in understanding the behavior of capacitors in AC circuits and is widely used in many applications, including filter circuits, resonance circuits, and power systems.