Which of the following properly describes capacitive reactance?

• A. Opposition to direct current
• B. Opposition to alternating current
• C. Flow of direct voltage
• D. Transfer of magnetic flux

Answer: (B)

Capacitive reactance refers specifically to the opposition that capacitors offer to alternating current (AC) in a circuit. It is a measure of how much a capacitor resists the flow of AC, which fluctuates in magnitude and direction. This resistance occurs because capacitors store energy in an electric field and their ability to charge and discharge affects the current flowing through them.

In an AC circuit, the frequency of the supply voltage plays a significant role in determining capacitive reactance. The general formula for capacitive reactance (Xc) is given by Xc = 1/(2πfC), where f is the frequency and C is the capacitance in farads. As the frequency increases, the capacitive reactance decreases, allowing more AC to pass. This relationship is crucial for the operation of AC circuits, particularly in filtering applications and timing circuits.

Understanding capacitive reactance is essential for electrical mechanics because it helps in designing circuits that involve capacitors, ensuring proper functionality and efficiency in AC applications.