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

View Answer

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 = log

_{e}(V

_{1}/V

_{2}).

2. A filter which passes without attenuation all frequencies up to the cut-off frequency f_{c} and attenuates all other frequencies greater than f_{c} is called?

a) high pass filter

b) low pass filter

c) band elimination filter

d) band pass filter

View Answer

Explanation: A filter is called a low pass filter if it passes all frequencies up to the cut-off frequency f

_{c}without attenuation and attenuates all other frequencies greater than f

_{c}. 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 f_{c} and passes all other frequencies greater than f_{c} is called?

a) band elimination filter

b) band pass filter

c) low pass filter

d) high pass filter

View Answer

Explanation: A filter is called high pass filter if attenuates all frequencies below a designated cut-off frequency f

_{c}and passes all other frequencies greater than f

_{c}. Thus the pass band of this filter is the frequency range above f

_{c}and the stop band is the frequency range below f

_{c}.

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

View Answer

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 f

_{2}-f

_{1}; f

_{1}is the lower cut-off frequency, f

_{2}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

View Answer

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.

6. The expression of the characteristic impedance of a symmetrical T-section is?

a) Z_{OT}=√(Z_{1}^{2}/4-Z_{1}Z_{2})

b) Z_{OT}=√(Z_{1}^{2}/4+Z_{1})

c) Z_{OT}=√(Z_{1}^{2}/4+Z_{2})

d) Z_{OT}=√(Z_{1}^{2}/4+Z_{1}Z_{2})

View Answer

Explanation: For a T-section, the value of input impedance when it is terminated in Z

_{o}is

Z

_{in}=(Z

_{1}/2)+(Z

_{2}((Z

_{1}/2)+Z

_{o}))/((Z

_{1}/2)+Z

_{2}+Z

_{o}) and Z

_{in}=Z

_{o}. On solving, the expression of the characteristic impedance of a symmetrical T-section is Z

_{OT}=√(Z

_{1}

^{2}/4+Z

_{1}Z

_{2}).

7. The expression of the open circuit impedance Z_{oc} is?

a) Z_{oc}=Z_{1}/2+Z_{2}

b) Z_{oc}=Z_{2}/2+Z_{2}

c) Z_{oc}=Z_{1}/2+Z_{1}

d) Z_{oc}=Z_{1}/2-Z_{2}

View Answer

Explanation: On open circuiting the port 2 of T-section, we get the expression of the open circuit impedance Z

_{oc}as Z

_{oc}=Z

_{1}/2+Z

_{2}.

8. The expression of short circuit impedance Z_{sc} is?

a) Z_{sc}=(Z_{1}^{2}-4Z_{1}Z_{2})/(2Z_{1}-4Z_{2})

b) Z_{sc}=(Z_{1}^{2}+4Z_{1}Z_{2})/(2Z_{1}+4Z_{2})

c) Z_{sc}=(Z_{1}^{2}-4Z_{1}Z_{2})/(2Z_{1}+4Z_{2})

d) Z_{sc}=(Z_{1}^{2}+4Z_{1}Z_{2})/(2Z_{1}-4Z_{2})

View Answer

Explanation: On short circuiting the port 2 of T-section, we get the expression of short circuit impedance Z

_{sc}as Z

_{sc}=(Z

_{1}/2)+((Z

_{1}/2)xZ

_{2})/((Z

_{1}/2)+Z

_{2}). On solving we get Z

_{sc}=(Z

_{1}

^{2}+4Z

_{1}Z

_{2})/(2Z

_{1}+4Z

_{2}).

9. The relation between Z_{OT}, Z_{oc}, Z_{sc} is?

a) Z_{OT}=√Z_{oc}Z_{sc}

b) Z_{oc}=√(Z_{OT} Z_{sc})

c) Z_{sc}=√(Z_{OT} Z_{oc})

d) Z_{oc}=√(Z_{OT} Z_{oc})

View Answer

Explanation: Z

_{oc}=Z

_{1}/2+Z

_{2}and Z

_{sc}=(Z

_{1}

^{2}+4Z

_{1}Z

_{2})/(2Z

_{1}+4Z

_{2}) => Z

_{oc}xZ

_{sc}=Z

_{1}Z

_{2}+Z

_{1}

^{2}/4 =Z

_{o}

^{2}T. The relation between Z

_{OT}, Z

_{oc}, Z

_{sc}is Z

_{OT}=√Z

_{oc}Z

_{sc}.

10. The value of sinhϒ/2 in terms of Z_{1} and Z_{2} is?

a) sinhϒ/2=√(4Z_{1}/Z_{2})

b) sinhϒ/2=√(Z_{1}/Z_{2})

c) sinhϒ/2=√(Z_{1}/4Z_{2})

d) sinhϒ/2=√(2Z_{1}/Z_{2})

View Answer

Explanation: sinhϒ/2=√((1/2(coshϒ-1)/(1/2(1+Z

_{1}/2Z

_{2}-1))). The value of sinhϒ/2 in terms of Z

_{1}and Z

_{2}is sinhϒ/2=√(Z

_{1}/4Z

_{2}).

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