TYPICAL QUESTIONS &
ANSWERS
PART
- I
OBJECTIVE TYPE QUESTIONS
Each
Question carries 2 marks.
Choose
correct or the best alternative in the following:
Q.1 The breakdown mechanism in a lightly doped p-n junction under reverse biased condition is called
(A) avalanche breakdown.
(B)
zener breakdown.
(C)
breakdown by
tunnelling.
(D) high voltage breakdown.
Ans: A
Q.2 In a CE – connected transistor amplifier with voltage – gain Av, the capacitance Cbc is amplified by a factor
(A)
(B) 
(C)
(D)
Ans: B
Q.3 For a large values of |VDS|, a FET – behaves as
(A)
Voltage controlled resistor.
(B)
Current controlled current source.
(C)
Voltage controlled
current source.
(D)
Current controlled
resistor.
Ans: C
Q.4 Removing bypass capacitor across the emitter-leg resistor in a CE amplifier causes
(A) increase in current gain. (B)
decrease in current gain.
(C) increase in voltage gain. (D)decrease in voltage
gain.
Ans: D
Q.5 For an op-amp having differential gain Av and common-mode gain Ac the CMRR is given by
(A)
(B)
(C) 
(D) 
Ans: B
Q.6 When a step-input is given to an op-amp integrator, the output will be
(A)
a ramp.
(B)
a sinusoidal wave.
(C)
a rectangular wave.
(D)
a triangular wave with dc bias.
Ans: A
Q.7 Hysteresis is desirable in Schmitt-trigger, because
(A)
energy is to be stored/discharged in parasitic capacitances.
(B)
effects of temperature would be compensated.
(C)
devices in the circuit should be allowed time for saturation
and desaturation.
(D)
it would prevent noise from causing false triggering.
Ans: C
Q.8 In a full-wave rectifier without filter, the ripple factor is
(A)
0.482 (B) 1.21
(C) 1.79 (D)
2.05
Ans: A
Q.9 A minterm of the Boolean-function, f(x, y, x) is
(A) 
(B)
(C)
x z (D)
(y +z) x
Ans: B
Q.10 The minimum number of flip-flops required to construct a mod-75 counter is
(A) 5 (B) 6
(C) 7 (D)
8
Ans: C
Q.11 Space charge region around a p-n junction
(A) does
not contain mobile carriers
(B) contains
both free electrons and holes
(C) contains one type of mobile carriers depending on the level
of doping of the p or n regions
(D) contains electrons only as free carriers
Ans: A
Q.12 The important characteristic of emitter-follower is
(A) high input impedance and high output impedance
(B) high input impedance and low output impedance
(C) low input impedance and low output impedance
(D) low input impedance and high output impedance
Ans: B
Q.13 In a JFET, at pinch-off voltage applied on the gate
(A) the drain current becomes almost zero
(B)
the drain current begins to
decrease
(C)
the drain current is almost at saturation value.
(D) the drain-to-source voltage is close to zero
volts.
Ans: C
Q.14 When an amplifier is provided with current series feedback, its
(A) input impedance increases and output impedance decreases
(B) input and output impedances both decrease
(C) input impedance decreases and output
impedance increases
(D) input and output impedances both increase
Ans: D
Q.15 The frequency of oscillation of a tunnel-collector oscillator having
L= 30μH and C = 300pf is nearby
(A) 267 kHz (B)
1677 kHz
(C) 1.68 kHz (D) 2.67
MHz
Ans: B 
Q.16 The open-loop gain of an op-amp available in the market may be around.
(A)
10–1 (B)
10
(C) 105 (D)
102
Ans: C
Q.17 The control terminal (pin5) of 555 timer IC is normally connected to ground through a capacitor (~ 0.01μF). This is to
(A) protect the IC from inadvertent
application of high voltage
(B) prevent false
triggering by noise coupled onto the pin
(C) convert the trigger
input to sharp pulse by differentiation
(D) suppress any negative
triggering pulse
Ans: B
Q.18 The value of ripple factor of a half-wave rectifier without filter is approximately
(A) 1.2 (B)
0.2
(C) 2.2 (D)
2.0
Ans: A
Q.19 The three variable Boolean expression xy + xyz + 
y + x
z
(A) 
(B) 
(C) 
(D)
Ans: C
Q.20 The fan-out of a MOS-logic gate is higher than that of TTL gates because of its
(A)
low input impedance (B)
high output impedance
(C) low output impedance (D) high input impedance
Ans: D
Q.21 In an intrinsic semiconductor, the Fermi-level is
(A) closer to the valence
band
(B) midway between conduction and valence band
(C) closer to the
conduction band
(D) within the valence band
Ans: C
Q.22 The reverse – saturation current of a silicon diode
(A) doubles for every 10°C
increase in temperature
(B) does not change with temperature
(C) halves for every 1°C
decrease in temperature
(D) increases by 1.5 times for every 2°C increment in temperature
Ans: A
Q.23 The common collector amplifier is also known as
(A) collector follower (B) Base follower
(C) Emitter follower (D) Source follower
Ans: C
Q.24 In class–A amplifier, the output current flows for
(A) a part of the cycle
or the input signal.
(B) the full cycle of the input signal.
(C) half the cycle of the input signal.
(D) 3/4th of the cycle of the input
signal.
Ans: B
Q.25 In an amplifier with negative feedback
(A) only the gain of the amplifier is affected
(B) only the gain and
bandwidth of the amplifier are affected
(C) only the input and
output impedances are affected
(D) All of the four
parameters mentioned above would be affected
Ans: D
Q.26 Wien bridge oscillator can typically generate frequencies in the range of
(A) 1KHz – 1MHz
(B) 1 MHz – 10MHz
(C) 10MHz – 100MHz
(D) 100MHz – 150MHz
Ans: A
Q.27 A differential amplifier, amplifies
(A) and mathematically
differentiates the average of the voltages on the two input lines
(B)
and differentiates the input waveform on one line when the
other line is grounded
(C)
the difference of voltages between the two input lines
(D)
and differentiates the sum of the two input waveforms
Ans: C
Q.28 The transformer utilization factor of a half-wave rectifier is approximately
(A) 0.6 (B)
0.3
(C) 0.9 (D)
1.1
Ans: B
0.286 
0.3
Q.29 The dual of the Boolean expression: x + y + z is
(A) 
(B) 
(C) 
(D)
Ans: C
Q.30 It is required to construct a counter to count upto 100(decimal). The minimum number of flip-flops required to construct the counter is
(A) 8 (B) 7
(C) 6 (D) 5
Ans: A
Q.31 The power conversion efficiency of an output
stage is defined as_______.
(A) (Load power + supply power) /
supply power
(B) (Load power + supply power) / (load
power-supply power)
(C) Load power / supply power
(D) Supply power / load power
Ans. (C)
Power
gain is defined as the ratio of output signal power to that of input signal
power.
Q.32 A highly stable
resonance characteristic is the property of a ____ oscillator.
(A) Hartley (B) Colpitts
(C) Crystal (D) Weinbridge
Ans. (C)
Q.33 The gate that assumes the 1 state, if and
only if the input does not take a 1
state is called________.
(A) AND gate (B) NOT gate
(C)
NOR gate (D) Both (B) & (C)
Ans. (D)
Y=
therefore output is high only when the values
of both A and B are 0.
Q.34 The width of depleted region of
a PN junction is of the order of a few tenths of a ___________.
(A) millimeter (B) micrometer
(C)
meter (D) nanometer
Ans. (B)
Q.35 For
NOR circuit SR flip flop the not allowed condition is ________.
(A) S=0, R=0. (B) S=0, R=1.
(C)
S=1, R=1. (D) S=1, R=0.
Ans. (C)
When
S=R=1 the output is subject to unpredictable behaviour when S and R return to 0 simultaneously.
Q.36 In negative feedback the return ratio is
__________.
(A) 0 (B) 1
(C)
greater than 0 (D) greater than 1
Ans. (C)
In
a negative feed back circuit, always the return ratio will be in the range of 0
to 1.
Q.37 A
phase shift oscillator uses __________________.
(A) LC tuning (B) Piezoelectric crystal
(C)
Balanced bridge (D) Variable frequency operation
Ans. (C)
Q.38 The voltage gain of basic CMOS is
approximately _________.
(A) (gmro)/2 (B) 2gmro
(C)
1 / (2gmro) (D) 2ro / gm
Ans. (A)
Q.39 Transistor is a
(A) Current controlled current device.
(B) Current controlled voltage device.
(C)
Voltage controlled current device.
(D)
Voltage controlled voltage device.
Ans. (A)
The output current depends on the input
current.
Q.40 A bistable multivibrator is a
(A)
Free running oscillator. (B) Triggered oscillator.
(C)
Saw tooth wave generator. (D) Crystal oscillator.
Ans. (B)
The
transistors would change their state of operation from ON to OFF and vice versa
depending on the external trigger provided.
Q.41 If the output voltage of a bridge rectifier
is 100V, the PIV of diode will be
(A)
100√2V (B) 200/π V
(C)
100πV (D) 100π/2 V
Ans. (D)
Peak
inverse voltage = max secondary voltage
Vdc=2Vm/ π =100
Vm=100 π /2
Q.42 In
the voltage regulator shown below, if the current through the load decreases,
(A)
The current through R1 will increase.
(B)
The current through R1 will decrease.
(C)
zener diode current will increase.
(D)
zener diode current will decrease.
Ans. (C)
Q.43 In Boolean algebra A + AB
(A)
A + B
(B) A + B
(C) A + B
(D) A +B
Ans. (A)
A.1+A
B= A (1+B) +A B = A + AB +A B = A+B (A +A) = A+B
Q.44 For a JFET, when VDS is increased
beyond the pinch off voltage, the drain current
(A) Increases
(B) decreases
(C) remains constant.
(D) First decreases and then increases.
Ans. (C)
At
pinch off voltage drain current reaches its maximum off. Now if we further increase VDS above Vp the
depletion layer expands at the top of the channel. The channel acts as a
current limiter & holds drain current constant
Q.45 The type of power amplifier which
exhibits crossover distortion in its output is
(A)
Class A (B) Class B
(C) Class AB (D) Class C
Ans. (B)
The
transistors do not conduct until the input signal is more than cut-in voltage
of the B-A junction. In class B, the devices being biased at cut-off, one
device stops conducting before the other device starts conducting leaving to Cross-over
distortion.
Q.46 The main advantage of a crystal
oscillator is that its output is
(A) 50Hz to 60Hz (B)
variable frequency
(C)
a constant frequency. (D) d.c
Ans. (C)
The
quality factor (Q) of a crystal as a resonating element is very high, of the order of thousands. Hence frequency of a
crystal oscillator is highly stable.
Q.47 The lowest output impedance is obtained in
case of BJT amplifiers for
(A) CB
configuration.
(B) CE configuration.
(C)
CC configuration.
(D) CE with RE
configuration.
Ans. (C)
The
output impedance in case of CC configuration is on the order of a few ohms.
(In
case of CB ≈ 450kΩ and in case of CE ≈ 45kΩ)
Q.48 N-channel FETs are superior to P-channel
FETs, because
(A) They have higher input impedance
(B) They have high switching time
(C) They consume less power
(D) Mobility of electrons is greater
than that of holes
Ans. (D)
Q.49 The upper cutoff frequency of an RC coupled
amplifier mainly depends upon
(A) Coupling capacitor
(B)
Emitter bypass capacitor
(C)
Output capacitance of signal source
(D)
Inter-electrode capacitance and stray shunt capacitance
Ans. (D)
Q.50 Just as a voltage amplifier amplifies
signal-voltage, a power amplifier
(A) Amplifies power
(B) Amplifies signal current
(C) Merely converts the signal ac power
into the dc power
(D) Merely converts the dc power into useful
ac power
Ans. (D)
Q.51 A radio frequency signal contains three
frequency components, 870 KHz, 875 KHz and 880 KHz. The signal needs to be
amplified. The amplifier used should be
(A) audio frequency amplifier (B) wide band amplifier
(C)
tuned voltage amplifier (D) push-pull amplifier
Ans. (C)
We
need to amplify 3 signal frequencies i.e., 870 kHz, 875 kHz and 880 kHz.
These
frequencies lie in a bandwidth of 10 kHz and we should use only tuned voltage
amplifiers to amplify them.
Q.52 An oscillator of the LC type that has a
split capacitor in the circuit is
(A) Hartley oscillator
(B) Colpitts oscillator
(C) Weinbridge oscillator
(D) R-C phase shift oscillator
Ans. (B)
We
have two capacitors in the tank circuit, which serve as a simple ac voltage
divider.
Q.53 The function of a bleeder
resistor in a power supply is
(A) the same as that of load resistor
(B) to ensure a minimum current drain
in the circuit
(C) to increase the output dc voltage
(D) to increase the output current
Ans. (B)
Q.54 In a bistable multivibrator circuit,
commutating capacitor is used
(A) to increase the base storage charge
(B) to provide ac coupling
(C) to increase the speed of response
(D) to provide the speed of
oscillations
Ans. (C)
The
commutating capacitor is used for the speedy transition of the state of the
bistable.
Q.55 n-type
silicon is obtained by
(A)
Doping with tetravalent element
(B) Doping with pentavalent element
(C) Doping with trivalent element
(D) Doping with a mixture of trivalent
and tetravalent element
Ans: (B)
The
pentavalent atom provides an excess electron while the other four form the covalent bond with the neighbouring
atoms. This excess free electron provides the n type conductivity.
Q.56 The forward characteristic of a diode has a
slope of approximately 50mA/V at a
desired
point. The approximate
incremental resistance of the diode is
(A) 50Ω (B) 35Ω
(C)
20Ω (D) 10Ω
Ans: (C)
Resistance
at any point in the forward characteristics is given by R= ΔV/ ΔI
= 1/50mA = 20Ω
Q.57 Two stages of BJT amplifiers are cascaded by
RC coupling. The voltage gain of the
first
stage is 10 and that of the
second stage is 20. The overall gain of
the coupled amplifier is
(A) 10x20
(B) 10+20
(C)
(10+20)2
(D) (10x20)/2
Ans: (A)
The voltage gain of a multistage
amplifier is equal to the product of the gains of the individual stages.
Q.58 In the voltage range, Vp < VDS
< BVDSS of an ideal JFET or MOSFET
(A)
The drain current varies linearly with VDS.
(B) The drain current is constant.
(C) The drain current varies
nonlinearly with VDS.
(D) The drain current is cut off.
Ans: (B)
It is the saturation region or
pinch off region, and drain current remains almost constant at its maximum value, provided VGS
is kept constant.
Q.59 In a voltage shunt negative feedback
amplifier system, the input resistance Ri and the output
resistance Ro of the basic
amplifier are modified as follows:
(A)
Ri is decreased and Ro increased.
(B) Both Ri and Ro are decreased.
(C) Both Ri and Ro are increased
(D) Ri is increased and Ro is
decreased.
Ans: (B)
Here,
a fraction of output voltage obtained by parallel sampling is applied in
parallel with the input voltage through feedback and both input and output
resistance decrease by a factor equal to (1+ βAv).
Q.60 The
use of crystal in a tunable oscillator
(A) Improves frequency stability.
(B) Increases the gain of the
oscillator.
(C) Helps to obtain optimum output
impedance.
(D) Facilitates generation of wide
range of frequencies.
Ans:
(A)
Piezoelectric
crystal is used as a resonant tank circuit. The crystal is made of quartz
material and provides a high degree of frequency stability.
Q.61 The large signal bandwidth of an opamp is
limited by its
(A)
(C) output impedance (D) input frequency
Ans: (B)
Q.62 Rectification efficiency of a full wave
rectifier without filter is nearly equal to
(A) 51% (B) 61%
(C)
71% (D) 81%
Ans: (D)
Efficiency
of a full wave rectifier is given by
[(2Im
/ π) 2 x RL] / [(Im
/ √2) 2 x (Rf + RL)] = 81%, when Rg is zero.
Q.63 When the temperature of a doped semiconductor is increased, its conductivity
(A) decreases.
(B) increases.
(C) does not change.
(D) increases or decreases depending on whether it is p- or n-type.
Ans:
B
Q.64 The main characteristics of a Darlington Amplifier are
(A) High input impedance, high output impedance and high current gain.
(B) Low input impedance, low output impedance and low voltage gain.
(C) High input impedance, low output impedance and high current gain.
(D) Low input impedance, low output impedance and high current gain.
Ans: C
Q.65 The transconductance, gm, of a JFET is computed at constant VDS, by the following:
(A) 
(B) 
(C) 
(D) 
Ans: A
Q.66 The feedback factor β at the frequency of oscillation of a Wien bridge oscillator is
(A) 3 (B) 
(C) 
(D) 
Ans: B
Q.67 In an amplifier with negative feedback, the bandwidth is
(A)
increased by a factor of β
(B) decreased by a factor of β
(C) increased by a factor of (1+Aβ)
(D) not affected at all by the feedback
where A = gain of the
basic amplifier and β = feedback factor
Ans:
C
Q.68 The ‘slew rate’ of an
operational amplifier indicates
(A)
how fast its output current can change
(B) how fast its output impedance can change
(C) how fast its output power can change
(D) how fast its output voltage can change
when a step input
signal is given.
Ans:
D
Q.69 In a clamping
circuit, the peak-to peak voltage of the waveform being clamped is
(A)
affected by the clamping
(B)
not affected by the clamping
(C)
determined by the clamping
voltage value
(D) determined by the ratio of rms voltage of the waveform and the clamping voltage
Ans: B
Q.70 Regulation of a.d.c. power supply is given by
(A) product of no-load output voltage and full-load current
(B) ratio of full-load output voltage and full-load current
(C) change in output voltage from no-load to full-load
(D) change in output impedance from no-load to full-load
Ans: D
Q.71 A ‘literal’ in Boolean Algebra means
(A) a variable inn its uncomplemented form only
(B) a variable ORed with its complement
(C) a variable in its complemented form only
(D) a variable in its complemented or uncomplemented form
Ans: D
Q.72 In an unclocked R-S flip-flop made of NOR gates, the forbidden input condition is
(A) R = 0, S = 0 (B) R = 1, S = 0
(C) R = 0, S = 1 (D) R = 1, S = 1
Ans: D
Q.73 The current amplification factor in CE configuration is
(A) α (B) β + 1
(C) 
(D) β
Ans: D
Q.74 A zener diode
(A) Has a high forward voltage rating.
(B) Has a sharp breakdown at low reverse voltage.
(C) Is useful as an amplifier.
(D) Has a negative resistance.
Ans: B
Q.75 N-channel FETs are superior to P-channel FETs, because
(A) They have a higher input impedance.
(B) They have high switching time.
(C) They consume less power.
(D) Mobility of electrons is greater than that of holes.
Ans:
Q.76 The maximum possible collector circuit efficiency of an ideal class A power amplifier is
(A) 15% (B) 25%
(C) 50% (D) 75%
Ans: C
Q.77 Negative feedback in an amplifier
(A) Reduces the voltage gain.
(B) Increases the voltage gain.
(C) Does not affect the voltage gain.
(D) Converts the amplifier into an oscillator.
Ans: A
Q.78 For generating 1 kHz signal, the most suitable circuit is
(A) Colpitts oscillator. (B) Hartley oscillator.
(C) Tuned collector oscillator. (D) Wien bridge oscillator.
Ans: D
Q.79 Phe output stage of an op-amp is usually a
(A)
(A) Complementary emitter follower.
(B)
(B) Transformer coupled class B amplifier.
(C) (C ) Class A power amplifier.
(D) (D) Class B amplifier.
Ans:
A
Q.80 When a sinusoidal voltage wave is fed to a Schmitt trigger, the output will be
(A) triangular wave. (B) asymmetric square wave.
(C) rectangular wave. (D) trapezoidal wave.
Ans:
B
Q.81 If the peak value of the input voltage to a half wave rectifier is 28.28 volts and no filter is use, the maximum dc voltage across the load will be
(A) 
. (B) 15 V.
(C) 9 V. (D) 14.14 V.
Ans:
C
Q.82 The logic gate which detects equality of two bits is
(A) EX-OR (B) EX-NOR
(C) NOR (D) NAND
Ans:
B
Q.83 The electron relaxation time of metal A is 
s, that of B is 
s. The ratio of resistivity of B to resistivity of A will be
(A) 4. (B) 2.0.
(C) 0.5. (D) 0.25.
Ans:
B
Q.84 The overall bandwidth of two identical voltage amplifiers connected in cascade will
(A) Remain the same as that of a single stage.
(B) Be worse than that of a single stage.
(C) Be better than that of a single stage.
(D) Be better if stage gain is low and worse if stage gain is high.
Ans: B
Q.85 Field effect transistor has
(A) large input impedance. (B) large output impedance.
(C) large power gain. (D) large votage gain.
Ans: A
Q.86 Which of the following parameters is used for distinguishing between a small signal and a large-signal amplifier?
(A) Voltage gain (B) Frequency response
(C) Harmonic Distortion (D) Input/output impedances
Ans:
D
Q.87 Which of the following parameters is used for distinguishing between a small signal and a large-signal amplifier?
(A) Instability (B) Bandwidth
(C) Overall gain (D) Distortion
Ans:
B
Q.88 If the feedback signal is returned to the input in series with the applied voltage, the input impedance ______.
(A) decreases (B) increases
(C) does not change (D) becomes infinity
Ans:
B
Q.89 Most of linear ICs are based on the two transistor differential amplifier because of its
(A) input voltage dependent linear transfer characteristic.
(B) High voltage gain.
(C) High input resistance.
(D) High CMRR
Ans: D
Q.90 The waveform of the output voltage for the circuit shown in Fig.1 (RC >> 1) is a
(A) sinusoidal wave (B) square wave
(C) series of spikes (D) triangular wave.
Ans: D
Q.91 A single phase diode bridge rectifier supplies a highly inductive load. The load current can be assumed to be ripple free. The ac supply side current waveform will be
(A) sinusoidal (B) constant dc.
(C) square (D) triangular
Ans:
C
Q.92 Which of the following Boolean rules is correct?
(A) A + 0 = 0 (B) A + 1 = 1
(C)
(D) 
Ans:
B
Q.93 A single phase diode bridge rectifier supplies a highly inductive load. The load current can be assumed to be ripple free. The ac supply side current waveform will be
(A) sinusoidal (B) constant dc.
(C) square (D) triangular
Ans:
C
Q.94 Which of the following Boolean rules is correct?
(A) A + 0 = 0 (B) A + 1 = 1
(C)
(D)
Ans:
B
; 
; i.e. 
.
= average current.
.
.
.
. Determine values of R1 and R2 to
obtain quiescent current ICQ = 100mA. If the collector current swing
, find the peak values of load current and load voltage.
Transformer turns ratio is primary 1:6 secondary.
is acceptable. Hence, choosing a reasonable value of 2.2K for
RB,
.
.
; given: Vmax = 50volts; RL =
400Ω, RF = 30 Ω
, 
, 
. Determine output voltage when 
.
. The minimum voltage reached by the collector due to signal
swing is 
. The dissipation in both the transistors totals 30 W. What
is the conversion efficiency of the amplifier?
and C =
, determine the output voltage.
, 
, B
, 
,
, 
, the transistor 
, 
=1.2 K
=10V and 
. Calculate (i) output voltage (ii) load current (iii) the
base current in the transistor (iv) zener current.
= 
