Filters (3.16) Learning Objectives Quiz

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Questions and Answers

What is the purpose of the low-pass filter described in the text?

To amplify high-frequency signals.

To pass all frequencies equally.

To block all frequencies equally.

To attenuate high-frequency signals. (correct)

What is the relationship between the input and output signal amplitudes when the applied signal frequency is much higher than the cut-off frequency?

The output amplitude is equal to the input amplitude.

The output amplitude is zero.

The output amplitude is significantly reduced compared to the input amplitude. (correct)

The output amplitude is half the input amplitude.

Which region of the ideal low-pass filter frequency response curve represents the frequencies that are passed by the filter?

The region below the cut-off frequency.

The region above the cut-off frequency.

The shaded area. (correct)

The unshaded area.

Which filter type allows only a specific range of frequencies to pass through while blocking frequencies outside that range?

Band pass filter Signup and view all the answers

What is the primary purpose of a tuned LCR circuit?

To oscillate at a specific frequency Signup and view all the answers

Which filter characteristic is primarily affected by the values of the inductor (L) and capacitor (C) in a filter circuit?

Resonant frequency Signup and view all the answers

In a high pass filter, which range of frequencies is allowed to pass through?

Only high frequencies Signup and view all the answers

Which filter type is commonly used to prevent spurious oscillations in electronic equipment?

Band stop filter Signup and view all the answers

What is one of the primary applications of low pass filters in communications systems?

Reducing interference from high frequencies Signup and view all the answers

At resonance, what type of impedance is observed in a series resonant circuit?

Resistive and low Signup and view all the answers

In a parallel resonant circuit at resonance, what type of impedance is observed?

Resistive and high Signup and view all the answers

What role do series LC circuits (resonant) play in terms of current flow?

Maximum opposition at resonant frequency Signup and view all the answers

What is the function of parallel LC circuits (resonant) in terms of current flow?

Maximum opposition at resonant frequency Signup and view all the answers

How do tuned circuits function as filters?

By rejecting all frequencies except the resonant frequency Signup and view all the answers

When selecting a specific radio station using an LC tuner, why does the tuner need to change the frequency?

To reject other stations' signals Signup and view all the answers

In an RC high-pass filter, what happens to the capacitive reactance (XC) as the frequency increases above the cut-off frequency?

XC decreases, allowing more voltage to appear across the resistor Signup and view all the answers

In an RL high-pass filter, what is the behavior of the inductive reactance (XL) at frequencies below the cut-off frequency?

XL is very low, causing most of the voltage to appear across the resistor Signup and view all the answers

What is the output voltage of an RC high-pass filter at the cut-off frequency (fCO) relative to the maximum applied voltage?

70.7% or 3 dB down from the maximum applied voltage Signup and view all the answers

How does the performance of RC and RL high-pass filters compare?

Performance of RC and RL high-pass filters is typically identical Signup and view all the answers

In an RC high-pass filter, what happens to the voltage across the capacitor at frequencies below the cut-off frequency?

Most of the voltage is dropped across the capacitor Signup and view all the answers

In an RL high-pass filter, what happens to the inductive reactance (XL) as the frequency increases above the cut-off frequency?

XL increases, causing more voltage to be dropped across the inductor Signup and view all the answers

What is the primary purpose of a band-pass filter?

To pass a narrow range of frequencies Signup and view all the answers

Which of the following is a basic configuration for a band-pass filter?

A series LC network Signup and view all the answers

What is the relationship between a band-pass filter and a resonant circuit?

Resonant circuits are used in both band-pass and band-stop filters Signup and view all the answers

What is the main difference between a band-pass filter and a band-stop filter?

Band-pass filters pass a narrow range of frequencies while band-stop filters pass a wide range of frequencies Signup and view all the answers

How does a series LC circuit act as a band-pass filter?

It passes currents with frequencies at or near its resonant frequency and opposes the passage of all currents with frequencies outside this band Signup and view all the answers

What is the primary application of band-pass and band-stop filters?

They are used in both communication and navigation equipment Signup and view all the answers

Study Notes

Filter Fundamentals

A low-pass filter's primary purpose is to allow low-frequency signals to pass through while attenuating high-frequency signals.
When the applied signal frequency is much higher than the cut-off frequency, the output signal amplitude is significantly lower than the input signal amplitude.

Ideal Low-Pass Filter

The region of the ideal low-pass filter frequency response curve that represents the frequencies that are passed by the filter is the passband.

Filter Types

A band-pass filter allows only a specific range of frequencies to pass through while blocking frequencies outside that range.
A tuned LCR circuit's primary purpose is to allow a specific range of frequencies to pass through while blocking frequencies outside that range.

Filter Characteristics

The values of the inductor (L) and capacitor (C) in a filter circuit primarily affect the filter's frequency response.

High Pass Filter

In a high-pass filter, high-frequency signals are allowed to pass through while low-frequency signals are attenuated.

Filter Applications

Band-pass filters are commonly used to prevent spurious oscillations in electronic equipment.
One of the primary applications of low-pass filters in communications systems is to remove high-frequency noise.

Resonance

At resonance, a series resonant circuit observes minimum impedance.
In a parallel resonant circuit at resonance, maximum impedance is observed.

Series and Parallel LC Circuits

Series LC circuits (resonant) play a role in blocking current flow at resonance.
Parallel LC circuits (resonant) play a role in allowing current flow at resonance.

Tuned Circuits as Filters

Tuned circuits function as filters by allowing only a specific range of frequencies to pass through while blocking frequencies outside that range.

Radio Tuning

When selecting a specific radio station using an LC tuner, the tuner needs to change the frequency to match the resonant frequency of the station.

High-Pass Filter Characteristics

In an RC high-pass filter, the capacitive reactance (XC) decreases as the frequency increases above the cut-off frequency.
In an RL high-pass filter, the inductive reactance (XL) increases at frequencies below the cut-off frequency.
The output voltage of an RC high-pass filter at the cut-off frequency (fCO) is 0.707 times the maximum applied voltage.
RC and RL high-pass filters have similar performance characteristics.
In an RC high-pass filter, the voltage across the capacitor decreases at frequencies below the cut-off frequency.
In an RL high-pass filter, the inductive reactance (XL) decreases as the frequency increases above the cut-off frequency.

Band-Pass Filters

The primary purpose of a band-pass filter is to allow a specific range of frequencies to pass through while blocking frequencies outside that range.
A basic configuration for a band-pass filter is a series LC circuit in series with a load resistor.
A band-pass filter is essentially a resonant circuit that allows a specific range of frequencies to pass through.
The main difference between a band-pass filter and a band-stop filter is that a band-pass filter allows a specific range of frequencies to pass through, whereas a band-stop filter blocks a specific range of frequencies.
A series LC circuit acts as a band-pass filter by allowing only a specific range of frequencies to pass through while blocking frequencies outside that range.
The primary application of band-pass and band-stop filters is in communication systems to filter out unwanted frequencies.

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Description

Test your knowledge on the operation and uses of low pass, high pass, band pass, and band stop filters. Questions cover defining their operations, identifying characteristics, and understanding the properties that affect resonant frequencies.