For high frequency, capacitor offers

A. High reactance

B. Low reactance

C. Cannot be predicted

D. Infinite reactance

When considering how capacitors behave at high frequencies, it's essential to understand the concept of reactance. Reactance is the opposition that a capacitor (or inductor) presents to alternating current (AC) due to its capacitance (or inductance). For capacitors, the reactance decreases as the frequency increases. Therefore, the correct answer to your question is B. Low reactance.

Understanding Capacitor Reactance

Capacitive reactance (Xc) can be calculated using the formula:

• Xc = 1 / (2πfC)

Where:

• Xc = capacitive reactance (in ohms)
• f = frequency (in hertz)
• C = capacitance (in farads)

How Frequency Affects Reactance

From the formula, you can see that as the frequency (f) increases, the value of Xc decreases. This means that at high frequencies, the capacitor allows more current to pass through, effectively offering low reactance. To illustrate this, think of a capacitor as a water reservoir:

• At low frequencies, the capacitor is like a large dam holding back water, creating high resistance to flow.
• At high frequencies, the dam opens up, allowing water to flow freely, which represents low resistance.

Practical Implications

In practical applications, this behavior is crucial. For instance, in audio circuits, capacitors are used to filter out unwanted high-frequency noise while allowing desired signals to pass through. Similarly, in power supply circuits, capacitors help smooth out voltage fluctuations, especially at higher frequencies.

Why Other Options Are Incorrect

Let’s briefly discuss why the other options do not apply:

• A. High reactance: This is incorrect because, as established, capacitors exhibit lower reactance at higher frequencies.
• C. Cannot be predicted: This is misleading; the behavior of capacitors at different frequencies can be accurately predicted using the reactance formula.
• D. Infinite reactance: This is not possible in practical scenarios. Infinite reactance would imply that no current could flow, which is not the case at high frequencies.

In summary, capacitors provide low reactance at high frequencies, allowing them to effectively pass AC signals while blocking DC. This property is fundamental in various electronic applications, making capacitors invaluable components in circuit design.