300+ Active Filter MCQ - Objective Question Answer for Active Filter Quiz

61. If the gain at center frequency is 10, find the quality factor of the narrow band-pass filter

A. 1
B. 2
C. 3
D. None of the mentioned

Answer: C

The gain of the narrow band-pass filter must satisfy the condition,

A_F= 2 × Q²

When Q=3,

=> 2 × Q² =2 × (3²) =18.

=> 10<18.

Hence the condition is satisfied when Q=3.

62. The advantage of a narrow band-pass filter is

A. f_c can be changed without changing gain
B. f_c can be changed without changing bandwidth
C. f_c can be changed without changing resistors
D. All of the mentioned

Answer: D

The narrow band-pass filter has multiple filters. The center frequency can be changed to a new frequency without changing the gain or bandwidth and is accomplished by changing the resistor to a new value which is given as

R’=R × (f_L/f_c)².

63. How many types of band elimination filters are present?

A. Three
B. Two
C. Four
D. None of the mentioned

Answer: B

Band-reject filters are also called as band elimination filters. They are classified into two types.

i) Wide band-reject filter and
ii) Narrow band-reject filter.

64. A narrow band-reject filter is commonly called as

A. Notch filter
B. Band step filter
C. Delay filter
D. All of the mentioned

Answer: A

A narrow band-reject filter is also called a notch filter because of its higher quality factor, Q (>10).

65. Find the expression for notch-out frequency?

A. f_N = 2πRC
B. f_N = 2π/RC
C. f_N = 1/2π × √(R/C.
D. f_N = 1/2πRC

Answer: D

The notch-out frequency is the frequency at which maximum attenuation occurs: it is given by f_N =1/2πRC.

66. The quality factor of passive twin T-network is increased by using

A. Inverting amplifier
B. Non-inverting amplifier
C. Voltage follower
D. Differential amplifier

Answer: C

The passive twin T-network has a selectively low figure of merit. The Q of the network can be increased significantly if it is used with the voltage follower.

67. Find out the application in which a narrow band-reject filter can be used?

A. Embedded system
B. Biomedical instrument
C. Digital computer
D. None of the mentioned

Answer: B

Notch filters or narrow band-reject filters are used in biomedical instruments for eliminating undesired frequencies.

68. Find the application of the area where all-pass filters are used?

A. Cathode ray oscilloscope
B. Television
C. Telephone wire
D. None of the mentioned

Answer: C

When signals are transmitted in transmission lines like telephone wires, they undergo a phase change, and all-pass filters are used to compensate for these phase changes.

69. Determine the output voltage for all the all-pass filters and express it in complex form?

A. V_O =V_in/ [(1-j2πfRC. /(1+ j2πfRC.].
B. V_O =V_in × [(1+j2πfRC. /(1- j2πfRC.].
C. V_O =V_in × [(1- j2πfRC. /(1+ j2πfRC.].
D. None of the mentioned

Answer: C
The output voltage of the all-pass filter is given as

V_O =V_in × [(1-j2πfRC. /(1+j2πfRC.] .

70. Determine the input frequency for the all-pass filter with a phase angle of 62^o. Consider the value of resistor and capacitor are 3.3kΩ and 4.7µF.

A. Input frequency= -7.65Hz
B. Input frequency= -6.77Hz
C. Input frequency= -3.89Hz
D. Input frequency= -9.65Hz

Answer: D

The phase angle is given as

Φ = -2tan^-1 × (2πfRC.

=> f=-tanΦ/4πRC

=-tan(62^o)/(4π × 3.3kΩ × 4.7µF)

= -1.88/0.1948 =-9.65Hz.

71. Determine the angle for the given circuit diagram, if the frequency of the input signal is 1khz

A. -45^o
B. -180^o
C. -270^o
D. -90^o

Answer: D

Phase angle Φ

=-2tan^-1 × (2πfRC/1)

= -2tan^-1 × (2π × 1kHz × 16kΩ × 0.01µF)

= -2tan^-1 × (1.0048)=-90^o.

72. The voltage gain magnitude of the all-pass filter is

A. Zero
B. One
C. Infinity
D. None of the mentioned

Answer: B

The magnitude of voltage gain of all-pass filter

|V_O /V_in| = √(1+(2π/RC.²) / √(1+(2 π/RC.²) =1.

73. What happens if the position of R and C are interchanged in the below circuit diagram?

A. V_in leads V_O
B. V_in lags V_O
C. V_O leads V_in
D. V_O leads V_in

Answer: C

For the circuit given, the phase angle changes from 0 to 180^o as frequency is varied from 0 to ∞. If the positions of R and C are interchanged, the phase shift and bandwidth input and output become positive. That is the output (V_O) leads to input (V_in).

74. Choose the incorrect statement “In wide band-reject filter”.

A. Low cut-off frequency of low pass filter must be larger than the high cut-off frequency of the high pass filter.

B. Low cut-off frequency of the high pass filter must be equal to the high cut-off frequency of the high pass filter.

C. Low cut-off frequency of high pass filter must be smaller than the high cut-off frequency of the low pass filter.

D. None of the mentioned

Answer: D

In a wide band-reject filter, the low cut-off frequency of high pass filter must be larger than the high cut-off frequency of the low pass filter.

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