Basic Electrical Science (A.C. Filter Networks)

1. The decibel is a measure of
(a) power
(b) voltage
(c) current
(d) power level

2. When the output voltage level of a filter decreases by – 3 dB, its absolute value changes by a factor of
(a) Ö2
(b) 1/ Ö2
(c) 2
(d) 1/2

3. 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

4. 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

5. In an RL low-pass filter, an attenuation of – 12 dB/octave corresponds to ........... dB/decade.
(a) – 6
(b) – 12
(c) – 20
(d) – 40

6. 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

7. In a simple high-pass RC filter, if the value of capacitance is doubled, the cut-off frequency is
(a) doubled
(b) halved
(c) tripled
(d) quadrupled

8. 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

9. 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

10. 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 cut off frequency would be ............... volt.
(a) 1
(b) 5
(c) 10 /Ö2
(d) 10Ö2

11. 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

12. 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

13. 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

14. 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

Answers

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

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