SELF-TEST
Consider a series RLC resonant circuit.
™ If the supply frequency changes, the resistance of the circuit
a) Remains constant
b) Increases with increase in frequency
c) Decreases with increase in frequency
Ans: (a)
™ If the supply frequency changes, the inductive reactance (XL)
a) Remains constant
b) Increases with increase in frequency
c) Decreases with increase in frequency
Ans: (b)
™ The total impedance of a circuit at resonance is
a) 0
b) Infinity
c) Maximum possible value
d) Minimum possible value
Ans: (d)
™ The power factor of a circuit at resonance is
a) 0
b) 0.5 lagging
c) 1
d) 0.5 leading
Ans: (c)
™ The selectivity of a resonant circuit is high when
a) The quality factor (Qs) is low
b) Qs is zero
c) Qs is high
Ans: (c)
™ At band frequency the power absorbed by the circuit is
a) Maximum
b) ¾ of maximum value
c) ½ of maximum value
d) ¼ of maximum value
e) 0
Ans: (c)
SELF-TEST
Consider an RLC series resonant circuit.
™ The frequency response characteristics can be considered symmetrical around the
resonant frequency when the quality factor (Qs) is:
a) Between 0 and 1
b) Between 1 and 10
c) Between 10 and infinity
Ans: (c)
™ For a circuit with a large value of Qs, the voltage across the resistor (VR) is:
a) Less than capacitor voltage(VC)
b) Equal to VC
c) Higher than VC
Ans: (c)
™ The peak of the inductor voltage (VL) occurs at a frequency
a) Smaller than the when VR peaks
b) Same as when VR peaks
c) Larger than when VR peaks
Ans: (c)
™ The peak of the capacitor voltage (VC) occurs at a frequency
a) Smaller than the when VR peaks
b) Same as when VR peaks
c) Larger than when VR peaks
Ans: (a)
™ The bandwidth of the circuit is large when the quality factor (Qs) is:
a) Large
b) Small
c) Negative
Ans: (b)
SELF-TEST
Consider the parallel RLC resonant circuit with “ideal” elements given below.
I
IR
IL
2KO
1mH
IC
+
10nF
_
™ 1) The total impedance seen by the source at resonance is
(a) 0
(b) 2KΩ
(c) 2MΩ
(d) infinity
Ans: (b)
™ The resonant frequency approximately is
(a) 10 Hz
(b) 100 KHz
(c) 160 KHz
(d) 500 KHz
Ans: (c)
™ The current through the resistance (IR) at resonance is
(a) 0
(b) 1 mA
(c) 2 mA
(d) 10 mA
Ans: (c)
™ The inductor current IL at resonance is
a) Equal to IR
b) Equal to IC
c) Equal and opposite to IC
d) Equal to I
Ans: (c)
SELF-TEST
1. A practical parallel “tank circuit” is equivalent to idea RLC parallel circuit if the
resistance of the coil is negligible:
(a) Yes
(b) No
Ans: (a)
2. A series circuit consisting of RS and XS can be converted to a resistance RP in parallel with
XP, where
R S2 + XS2
RP =
XS
(a) Yes
R S2 + XS2
XP =
RS
(b) No
Ans: (b)
3. The exact condition for resonance of a practical tank circuit when
a)ωp =
1
LC
b)ωp =
1 R S2
−
LC L2
c)ωp =
1 RS
−
LC L
Ans: (b)
4. A resonant condition in a series-parallel circuit arises when:
a) The frequency is maximum
b) The frequency is minimum
c) The impedance is totally resistive
d) The impedance is totally reactive
SELF-TEST
The expression for a damped sinusoid voltage in time domain is
v(t)= 240 e-10t cos (20t + 600) volts
™ The phasor voltage is
a)
b)
c)
d)
240∠o V
240∠60 V
240∠20 V
240∠ − 10 V
Ans: (b)
™ The neper frequency (σ) is
a) 20
b) 60
c) 240
d) 10
Ans: (d)
™ The angular frequency (ω) is
a) 240
b) 10
c) 20
d) 60
Ans: (c)
™ If this voltage is applied to a resistor R=2 Ω, the phasor current is
a)240∠00 A
b)120∠00 A
c)120∠600 A
d)240∠900 A
Ans: (c)
™ If this viltage is applied to an inductance of 2H, the phasor current is
a)120∠600 A
b)120∠ − 300 A
c)60∠ − 300 A
d)60∠600 A
Ans: (c)
SELF-TEST
Consider the series parallel circuit given in the following circuit. The expression for the
source voltage in time domain is
v(t)= 4 e-t cos (2t -900) volts
L=2H
V g (t )
R= 4Ω
+_
C =1F
4
™ The complex frequency (s) in this problem is
a) 1+j2
b) -1-j2
c) -1+j2
d) 4-j1
Ans: (c)
™ The complex impedance offered by the impedance is
a) s/2
b) 2/s
c) 2s
d) 4 +2s
Ans: (c)
™ The complex frequency offered by the capacitance is
a)1/(4s)
b) 4/s
c) s/4
d) 4s
Ans: (b)
™ The total impedance seen by the source is
4s
s+2
2
b)
s+2
s+4
c)
s+2
2s
d)
s+4
a)
Ans: (a)
SELF-TEST (21)
1. Consider the following RC circuit.
The transfer function
Vo (s)
is
Vi (s)
K
s+a
Ks
b)
s+a
K
c) 2
s + as + b
Ks
d) 2
s + as + b
a)
Here, K, a, b depend on R and C.
Ans: (a)
2. For a transfer function
H(s) =
4(s + 2)
s + 2s + 5
2
™ The poles are at
(a) − 1 ± j3
(b) − 1 ± j2
(c)1 ± j2 (d)1 ± j3
Ans: (b)
™ The zeroes are at
(a) 0,2
(b) 0, -2
(c) -2
(d) 0
Ans: (c)
SELF-TEST (21)
1. The possible pole-zero locations for the transfer function
H(s) =
15s 2 + 45s
s 2 + 6s + 8
are given in the following 3 diagrams. State the correct answer.
a)
b)
c)
Ans: (a)
2. The transfer function for a circuit is
H(s) =
3s(s + 3)
(s + 1)(s + 2)
The natural response is (A and B are constants)
a) A e-2t + B e-3t
b) A e-2t + B e-t
c) A e2t + B e3t
d) A e2t + B et
Ans: (b)