AIIMS 2005 Physics Filters MCQ Question

To determine why the correct answer is A) tuned filter, we first need to understand what a tuned filter is and how it operates compared to the other options listed.

1. Explanation of the Correct Answer: Tuned Filter

A tuned filter is designed to select a specific frequency while rejecting others. It is typically constructed using a combination of inductors (L) and capacitors (C) to create a resonant circuit. The resonant frequency $f_0$ of the circuit can be calculated using the formula:

$$f_0 = \frac{1}{2\pi\sqrt{LC}}$$

In a tuned filter circuit, when the input signal frequency matches $f_0$, the circuit exhibits maximum output (resonance), allowing that frequency to pass through while attenuating frequencies that are significantly different from $f_0$. This characteristic is the hallmark of tuned filters, hence the correct answer.

2. Clarification of Incorrect Options

• B) Low Pass Filter: A low pass filter allows signals with a frequency lower than a certain cutoff frequency to pass and attenuates frequencies higher than that cutoff. While it can be realized with an LC circuit, it does not have the selective frequency response that a tuned filter provides.

• C) High Pass Filter: Conversely, a high pass filter allows signals with frequencies higher than a certain cutoff frequency to pass while attenuating lower frequencies. Like the low pass filter, it does not target a specific resonant frequency but instead focuses on the general frequency range above the cutoff.

• D) Rectifier: A rectifier converts alternating current (AC) to direct current (DC). It does not perform frequency selection like a tuned filter. Rectifiers typically use diodes and are not concerned with frequency responses, making this option irrelevant in this context.

Summary of Concepts and Formulas

• Tuned Filter: Selects a specific frequency $f_0$.
• Resonant Frequency Formula:

$$f_0 = \frac{1}{2\pi\sqrt{LC}}$$

• Low Pass Filter: Attenuates frequencies above a certain cutoff.
• High Pass Filter: Attenuates frequencies below a certain cutoff.
• Rectifier: Converts AC to DC, not frequency selective.

Conclusion

Given that the circuit is a tuned filter, it specifically resonates at a certain frequency and allows signals at that frequency to pass while rejecting others. This distinguishes it from low pass, high pass filters, and rectifiers, which have different operational characteristics. Therefore, the correct answer is A) tuned filter.