# Network Theory Questions and Answers – Filter Networks

This set of Network Theory Multiple Choice Questions & Answers (MCQs) focuses on “Filter Networks”.

1. The value of one decibel is equal to?
a) 0.115 N
b) 0.125 N
c) 0.135 N
d) 0.145 N

Explanation: The value of one decibel is equal to 0.115 N. One decibel = 0.115 N where N is the number of nepers and N = loge(V1/V2).

2. A filter which passes without attenuation all frequencies up to the cut-off frequency fc and attenuates all other frequencies greater than fc is called?
a) high pass filter
b) low pass filter
c) band elimination filter
d) band pass filter

Explanation: A filter is called a low pass filter if it passes all frequencies up to the cut-off frequency fc without attenuation and attenuates all other frequencies greater than fc. This transmits currents of all frequencies from zero up to the cut-off frequency.

3. A filter which attenuates all frequencies below a designated cut-off frequency fc and passes all other frequencies greater than fc is called?
a) band elimination filter
b) band pass filter
c) low pass filter
d) high pass filter

Explanation: A filter is called high pass filter if attenuates all frequencies below a designated cut-off frequency fc and passes all other frequencies greater than fc. Thus the pass band of this filter is the frequency range above fc and the stop band is the frequency range below fc.

4. A filter that passes frequencies between two designated cut-off frequencies and attenuates all other frequencies is called?
a) high pass filter
b) band elimination filter
c) band pass filter
d) low pass filter

Explanation: A band pass filter passes frequencies between two designated cut-off frequencies and attenuates all other frequencies. A band pass filter has two cut-off frequencies and will have the pass band f2-f1; f1 is the lower cut-off frequency, f2 is the upper cut-off frequency.

5. A filter that passes all frequencies lying outside a certain range, while it attenuates all frequencies between the two designated frequencies is called?
a) low pass filter
b) high pass filter
c) band elimination filter
d) band pass filter

Explanation: A band elimination filter passes all frequencies lying outside a certain range, while it attenuates all frequencies between the two designated frequencies. It is also referred to as band stop filter.
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6. The expression of the characteristic impedance of a symmetrical T-section is?
a) ZOT=√(Z12/4-Z1Z2)
b) ZOT=√(Z12/4+Z1)
c) ZOT=√(Z12/4+Z2)
d) ZOT=√(Z12/4+Z1Z2)

Explanation: For a T-section, the value of input impedance when it is terminated in Zo is
Zin=(Z1/2)+(Z2((Z1/2)+Zo))/((Z1/2)+Z2+Zo) and Zin=Zo. On solving, the expression of the characteristic impedance of a symmetrical T-section is ZOT=√(Z12/4+Z1Z2).

7. The expression of the open circuit impedance Zoc is?
a) Zoc=Z1/2+Z2
b) Zoc=Z2/2+Z2
c) Zoc=Z1/2+Z1
d) Zoc=Z1/2-Z2

Explanation: On open circuiting the port 2 of T-section, we get the expression of the open circuit impedance Zoc as Zoc=Z1/2+Z2.

8. The expression of short circuit impedance Zsc is?
a) Zsc=(Z12-4Z1Z2)/(2Z1-4Z2)
b) Zsc=(Z12+4Z1Z2)/(2Z1+4Z2)
c) Zsc=(Z12-4Z1Z2)/(2Z1+4Z2)
d) Zsc=(Z12+4Z1Z2)/(2Z1-4Z2)

Explanation: On short circuiting the port 2 of T-section, we get the expression of short circuit impedance Zsc as Zsc=(Z1/2)+((Z1/2)xZ2)/((Z1/2)+Z2). On solving we get Zsc=(Z12+4Z1Z2)/(2Z1+4Z2).

9. The relation between ZOT, Zoc, Zsc is?
a) ZOT=√ZocZsc
b) Zoc=√(ZOT Zsc)
c) Zsc=√(ZOT Zoc)
d) Zoc=√(ZOT Zoc)

Explanation: Zoc=Z1/2+Z2 and Zsc=(Z12+4Z1Z2)/(2Z1+4Z2) => ZocxZsc=Z1Z2+Z12/4 =Zo2T. The relation between ZOT, Zoc, Zsc is ZOT=√ZocZsc.

10. The value of sinh⁡ϒ/2 in terms of Z1 and Z2 is?
a) sinh⁡ϒ/2=√(4Z1/Z2)
b) sinh⁡ϒ/2=√(Z1/Z2)
c) sinh⁡ϒ/2=√(Z1/4Z2)
d) sinh⁡ϒ/2=√(2Z1/Z2)

Explanation: sinhϒ/2=√((1/2(coshϒ-1)/(1/2(1+Z1/2Z2-1))). The value of sinh⁡ϒ/2 in terms of Z1 and Z2 is sinh⁡ϒ/2=√(Z1/4Z2).

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