Question

For high frequency, a capacitor offers (a) More reactance (b) Less reactance (c) Zero reactance (d) Infinite reactance

Short answer

(b) Less reactance

Step-by-step solution

1. Understanding Capacitive Reactance

Capacitive reactance refers to the capacitor's resistance to alternating current (AC) signals. This resistance changes based on the frequency of the input signal. To understand how a capacitor behaves with high-frequency signals, we need to consider the formula for capacitive reactance, which is given by: \(X_C = \frac{1}{2\pi fC}\) Here, \(X_C\) is the capacitive reactance, \(f\) is the frequency of the signal, and \(C\) is the capacitor's capacitance.

2. Analyzing the Capacitive Reactance Formula for High Frequencies

Let's consider the capacitive reactance formula and analyze how \(X_C\) changes based on the frequency \(f\). Since \(X_C\) is inversely proportional to the frequency, we can deduce that as the frequency of the input signal increases, the capacitive reactance decreases, and vice versa. Therefore, for high-frequency signals, a capacitor would offer a lower reactance. Now that we have analyzed the behavior of a capacitor for high-frequency signals, we can choose the correct option from the given alternatives.

3. Final Selection

Based on our analysis, we can select the correct option: (b) Less reactance A capacitor offers less reactance for high-frequency input signals.

Key concepts

High Frequency Behavior in Capacitors

Capacitors are crucial components in electrical circuits and their behavior changes with the frequency of the input signals they encounter. When the frequency of the input signal is high, capacitors act differently compared to when they face low-frequency signals. This change can be understood through the concept of capacitive reactance, which is the effective resistance a capacitor presents to alternating current (AC).

At high frequencies, there is a remarkable reduction in reactance. This is because capacitive reactance, denoted by \(X_C\), is inversely related to the frequency \(f\) of the signal. According to the formula \(X_C = \frac{1}{2\pi fC}\), as the frequency increases, the value of \(X_C\) decreases significantly. This means that the capacitor offers less opposition to AC at high frequencies, allowing the signals to pass through more easily. Understanding this behavior is essential when designing circuits that operate at different frequencies.

Alternating Current (AC)

Alternating current (AC) is an essential element in almost every modern electrical system. Unlike direct current (DC), which flows consistently in one direction, AC current periodically reverses its direction. This dynamic nature of AC is what makes capacitors uniquely reactive depending on the frequency of the AC signal.

The ability of capacitors to store and release energy makes them particularly useful in AC circuits. During each cycle of AC, the capacitor charges and discharges. This process creates a phase difference between voltage and current, with the current leading the voltage. Capacitors serve vital roles in AC circuits by smoothing out fluctuations, filtering signals, and determining the frequency response. It's crucial to understand how capacitors react to AC to effectively utilize them in applications like tuning radios, managing power supply lines, and in audio equipment.

Inversely Proportional Relationship

In physical sciences and engineering, an inversely proportional relationship describes a scenario where an increase in one variable leads to a proportional decrease in another. In capacitive reactance, we observe such a relationship between the reactance \(X_C\) and the frequency \(f\).

Simply put, as the frequency of the input signal increases, the capacitive reactance decreases, which is logically described by the formula \(X_C = \frac{1}{2\pi fC}\). This inverse relation is key to many practical applications. For instance:

• In high-frequency AC systems, capacitors exhibit low reactance, making them ideal for bypassing.
• In tuning circuits, adjusting the frequency can alter reactance, thus changing the circuit's filtering properties.

Grasping this inversely proportional nature helps engineers and technicians design effective electronic circuits where precise control of AC signals is required.