### 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 f

_{c}. At 2 f_{c}, attenuation is – 6 dB. At
10 f

_{c}, 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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