Short notes
Objective questions (Answers are given below)
- The decibel is a measure of
(a) power (b) voltage
(c) current (d) power level - When the output voltage level of a filter
decreases by – 3 dB, its absolute value
changes by a factor of
(a) 2 (b) 1/ 2
(c) 2 (d) 1/2 - The frequency corresponding to half-power
point on the response curve of a filter is
known as —
(a) cutoff (b) upper
(c) lower (d) roll-off - In a low-pass filter, the cutoff frequency is
represented by the point where the output
voltage is reduced to — per cent of the input
voltage.
(a) 50 (b) 70.7
(c) 63.2 (d) 33.3 - In an RL low-pass filter, an attenuation of
– 12 dB/octave corresponds to ……….. dB/
decade.
(a) – 6 (b) – 12
(c) – 20 (d) – 40 - A network which attenuate a single band of
frequencies and allows those on either side
to pass through is called …….. filter.
(a) low-pass (b) high-pass
(c) bandstop (d) bandpass - In a simple high-pass RC filter, if the value of
capacitance is doubled, the cutoff frequency is
(a) doubled (b) halved
(c) tripled (d) quadrupled - In a simple high-pass RL filter circuit, the
phase difference between the output and
input voltages at the cutoff frequency is ….
degrees.
(a) – 90 (b) 45
(c) – 45 (d) 90
- In a simple low-pass RC filter, attenuation is
– 3 dB at fc. At 2 fc, attenuation is – 6 dB. At
10 fc, the attenuation would be …. dB.
(a) – 30 (b) – 20
(c) – 18 (d) – 12 - An a.c. signal of constant voltage 10 V and
variable frequency is applied to a simple
high-pass RC filter. The output voltage at ten
times the cutoff frequency would be
…………… volt.
(a) 1 (b) 5
(c) 10 / 2 (d) 10 2 - When two simple low-pass filters having
same values of R and C are cascaded, the
combined filter will have a roll-off of ……
dB/decade.
(a) – 20 (b) – 12
(c) – 40 (d) – 36 - An a.c. signal of constant voltage but with
frequency varying from dc to 25 kHz is
applied to a high-pass filter. Which of the
following frequency will develop the greatest
voltage at the output load resistance?
(a) d. (b) 15 kHz
(c) 10 kHz (d) 25 kHz - A voltage signal source of constant amplitude
with frequency varying from dc to 25 kHz is
applied to a low-pass filter. Which frequency
will develop greatest voltage across the
output load resistance?
(a) d.c. (b) 10 kHz
(c) 15 kl (d) 25 kHz - The output of a filter drops from 10 to 5 V
as the frequency is increased from 1 to 2
kHz. The dB change in the output voltage is
(a) – 3 dB/decade
(b) – 6 dB/octave
(c) 6 dB/octave
(d) – 3 dB/octave
1.d 2. b 3. a 4. b 5. d 6. c 7. b 8. b 9. b 10. a 11. c 12. d 13. a 14. b