Electronics Engineering Multiple Choice Questions and Answers (MCQs) Part 3:
106. Which of the transistor models is most preferred for the analysis of a transistor circuit both at mid-band and at high frequencies?
(a) h-parameter model.
(b) y-parameter model.
(c) s-parameter model.
(d) hybrid -π model.
Answer : (d) hybrid -π model.
107. The common emitter current gain-bandwidth product of a transistor (fT) is defined as the frequency at which
(a) alpha of the transistor falls by 3 dB.
(b) beta of the transistor falls by 3 dB.
(c) beta of the transistor falls to unity.
(d) power gain of the transistor falls to unity.
Answer : (c) beta of the transistor falls to unity.
108. A cascade amplifier stage is equivalent to
(a) a common emitter stage followed by a common base stage.
(b) a common base stage followed by an emitter follower.
(c) an emitter follower stage followed by a common base stage.
(d) a common base stage followed by a common emitter stage.
Answer : (a) a common emitter stage followed by a common base stage.
109. Consider the following statements in respect of a transistor R-C coupled amplifier:
1. The low frequency response is determined by the transistor junction capacitors.
2. The high frequency response is limited by coupling capacitors.
3. The Miller capacitance reduces the gain at high frequencies.
4. As the gain is increased the bandwidth gets reduced.
Which of these statements are correct?
(a) 1 and 2.
(b) 2 and 3.
(c) 3 and 4.
(d) 1 and 4.
Answer : (c) 3 and 4.
110. Which of the following components control the high frequency response of the R-C coupled amplifier ?
1. Parasitic capacitances of the transistors.
2. Coupling capacitance.
3. Stray capacitances.
4. Wiring capacitance.
Select the correct answer using the code given below :
(a) 1 and 2 only.
(b) 2 and 3 only.
(c) 3 and 4 only.
(d) 1, 3, and 4.
Answer : (d) 1, 3, and 4.
111. A amplifier has two identical cascaded stages. Each stage has bandwidth of 20 kHz. The overall bandwidth shall approximately by equal to
(a) 10 kHz.
(b) 12.9 kHz.
(c) 20 kHz.
(d) 28.3 kHz.
Answer : (b) 12.9 kHz.
112. In a class A amplifier, there will be a worst condition when
(a) signal input is zero.
(b) signal input is maximum.
(c) load resistance is high.
(d) there is a transformer coupling.
Answer : (a) signal input is zero.
113. Consider the following statements:
A class-B amplifier
1. is biased just at cut-off.
2. has a high theoretical efficiency of 78.5% because its quiescent current is low.
3. is biased at the midpoint of load time.
Of these statements
(a) 2 and 3 are correct.
(b) 1 alone is correct.
(c) 2 alone is correct.
(d) 1 and 2 are correct.
Answer : (d) 1 and 2 are correct.
114. Which one of the following statements is correct ?
The efficiency of class B push-pull amplifiers is much higher than that of class-A amplifiers primarily because
(a) the distortion is kept within acceptable limits.
(b) one half of the input signal is amplified using one transistor and the other half is phase inverted and fed to the other transistor.
(c) matched pair transistors are used in the class B push-pull operation.
(d) the quiescent dc current is avoided.
Answer : (d) the quiescent dc current is avoided.
115. A class-B push-pull type amplifier with transformer coupled load uses two transistors rated 10 W each. What is the maximum power output one can obtain at the load from this circuit?
(a) 40 W
(b) 50 W
(c) 60 W
(d) 70 W
Answer : (b) 50 W
116. In a transconductance amplifier, it is desirable to have
(a) a large input resistance and a large output resistance
(b) a large input resistance and a small output resistance
(c) a small input resistance and a large output resistance
(d) a small input resistance and a small output resistance
Answer : (a) a large input resistance and a large output resistance
117. The open-loop voltage gain of an amplifier is 240. The noise level in the output without feedback is 100 mV. If a negative feedback with β = 1/60 is used, the noise level in the output will be
(a) 1.66 mV
(b) 2.4 mV
(c) 4.0 mV
(d) 20 mV
Answer : (d) 20 mV
118. In the shunt series feedback amplifier, the basic amplifier and the feedback network are parallel connected at the input and series connected at the output. The signal sampled and the summing down will be respectively
(a) current and current
(b) current and voltage
(c) voltage and current
(d) voltage and voltage
Answer : (d) voltage and voltage
119. In a shunt-shunt negative feedback amplifier, as compared to the basic amplifier
(a) both, input and output impedances, decrease.
(b) input impedance decreases but output impedance increases.
(c) input impedance increases but output impedance decreases.
(d) both input and output impedances increase.
Answer : (a) both, input and output impedances, decrease.
120. In a negative feedback amplifier, when is the input impedance increased?
(a) If the signal sampled is a voltage.
(b) If the signal sampled is a current.
(c) If the feedback signal is a voltage.
(d) If the feedback signal is a current.
Answer : (c) If the feedback signal is a voltage.
121. Which one of the following type of negative feedback increases the input resistance and decreases the output resistance of amplifier?
(a) Current series feedback.
(b) Voltage series feedback.
(c) Current shunt feedback.
(d) Voltage shunt feedback.
Answer : (b) Voltage series feedback.
122. In a common emitter amplifier, the unbypassed emitter resistance provides
(a) voltage shunt feedback.
(b) current series feedback.
(c) negative voltage feedback.
(d) positive current feedback.
Answer : (b) current series feedback.
123. A Darlington amplifier has a
(a) large current gain and high input resistance.
(b) large voltage gain and low output resistance.
(c) small voltage gain and low input resistance.
(d) small current gain and high output resistance.
Answer : (a) large current gain and high input resistance.
124. For tuned radio-frequency we use
(a) class A amplifier.
(b) class B amplifier.
(c) class AB amplifier.
(d) class C amplifier.
Answer : (d) class C amplifier.
125. If the Q of a single-stage single-tuned amplifier is doubled, then its bandwidth will
(a) remain same.
(b) become half.
(c) become double.
(d) become four times.
Answer : (b) become half.
126. In a cascaded differential amplifier
(a) R-C coupling is used.
(b) direct coupling is used.
(c) ac coupling is used.
(d) ac or dc coupling may be used.
Answer : (b) direct coupling is used.
127. A change in the value of the emitter resistance Re in a differential amplifier
(a) affects the difference mode gain, Ad.
(b) affects the common mode gain, Ac.
(c) affects both Ad and Ac.
(d) does not affect either Ad or Ac.
Answer : (b) affects the common mode gain, Ac.
128. A differential amplifier is invariably used in the input stage of all op-amps. This is done basically to provide the op-amps with a very high
(a) CMRR.
(b) bandwidth.
(c) slew rate.
(d) open-loop gain.
Answer : (a) CMRR.
129. The Barkhausen criterion for sustained oscillations is given by
(a) Aβ = 1
(b) |Aβ| ≥ 1
(c) |Aβ| < 1
(d) ∠Aβ = 180°
Answer : (b) |Aβ| ≥ 1
130. Consider the following statements :
1. A Hartley oscillator circuit uses a tapped inductor for inductive feedback.
2. Oscillator circuit can be operated in class A condition for better waveshape.
3. Frequency stabilization is obtained by the use of automatic biasing.
Which of the statements given above are correct ?
(a) 1, 2 and 3.
(b) 1 and 2.
(c) 2 and 3.
(d) 1 and 4.
Answer : (b) 1 and 2.
131. The highest frequency stability is achieved by using an oscillator of the type:
(a) Colpitts.
(b) Crystal controlled.
(c) Hartley.
(d) RC oscillator.
Answer : (b) Crystal controlled.
132. Which one of the following statements is correct of phase-shift type and Wein bridge type R-C oscillators ?
(a) Both use positive feedback.
(b) The former uses positive feedback while the latter uses both positive and negative feedback.
(c) The former uses both positive and negative feedback while the latter uses positive feedback only.
(d) Both use negative feedback.
Answer : (b) The former uses positive feedback while the latter uses both positive and negative feedback.
133. Which one of the following oscillators is well suited for the generation of wide range audio-frequency sine waves?
(a) RC phase-shift oscillator.
(b) Wien-bridge oscillator.
(c) Colpitts oscillator.
(d) Hartley oscillator.
Answer : (b) Wien-bridge oscillator.
134. Modulation is primarily accomplished to
(a) produce sidebands.
(b) mix two waves of different frequencies.
(c) transmit audio-frequency signals over long distances.
(d) improve transmission efficiency.
Answer : (c) transmit audio-frequency signals over long distances.
135. Amplitude modulation is used for broadcasting because
(a) it is more noise immune than other modulation systems.
(b) it consumes less transmitting power.
(c) its use avoids receiver complexity.
(d) no other modulation system can provide the necessary bandwidth for high fidelity.
Answer : (c) its use avoids receiver complexity.
136. On modulating a carrier of frequency fc by an audio signal fs the following components have resulted:
fc, fc + fs and fc – fs
What is this type of modulation likely to be?
(a) Amplitude modulation DSB.
(b) Single sideband modulation.
(c) Frequency modulation only.
(d) Amplitude modulation or frequency modulation.
Answer : (d) Amplitude modulation or frequency modulation.
137. A balanced modulator is used in the generation of which of the following?
(a) DSB-SC signal.
(b) FM signal.
(c) PM signal.
(d) PAM signal.
Answer : (a) DSB-SC signal.
138. One of the advantage of base modulation over collector modulation of a transistor Class C amplifier is
(a) the lower modulating power required.
(b) higher power output per transistors.
(c) better efficiency.
(d) better linearity.
Answer : (a) the lower modulating power required.
139. In an AM system, for satisfactory operation, carrier frequency must be n times the bandwidth of message signal. What is the value of n?
(a) > 2
(b) > 5
(c) > 10
(d) > 50
Answer : (d) > 50
140. In AM, the modulation index lies between
(a) -1 and 1
(b) 0 and 1
(c) 1 and ∞
(d) -∞ and ∞
Answer : (b) 0 and 1
141. One of the advantages of base modulation over collector modulation of a transistor class C amplifier is
(a) lower modulating power required.
(b) higher power output per transistor.
(c) better efficiency.
(d) better transmission.
Answer : (a) lower modulating power required.
142. Consider the following types of modulation:
1. Amplitude modulation.
2. Frequency modulation.
3. Pulse modulation.
4. Phase modulation.
Which of the above modulations are used for telecasting TV programmes?
(a) 3 and 4.
(b) 2 and 3.
(c) 1 and 2.
(d) 1 and 4.
Answer : (c) 1 and 2.
143. What is the assigned bandwidth of each of the channels in the AM broadcast band?
(a) 5 kHz
(b) 10 kHz
(c) 15 kHz
(d) 200 kHz
Answer : (b) 10 kHz
144. Consider the following:
1. Filter system.
2. Phase-shift method.
3. Third method.
4. Balanced modulator.
Which of these can be used to remove unwanted sidebands in SSB?
(a) 1, 2 and 4.
(b) 1, 2 and 3.
(c) 2,3 and 4.
(d) 1, 3 and 4.
Answer : (b) 1, 2 and 3.
145. The ring modulator is generally used for
(a) generating SSB/SC signal.
(b) generating ISI signal.
(c) generating wideband signal.
(d) generating DSB/SC signal.
Answer : (d) generating DSB/SC signal.
146. In frequency modulation
(a) the frequency of the carrier remains constant.
(b) the amplitude of carrier remains constant.
(c) the amplitude of the carrier wave is varied.
(d) the frequency of the signal is made equal to the carrier frequency.
Answer : (b) the amplitude of carrier remains constant.
147. Why does an FM radio station perform better than an AM station radiating the same total power ?
(a) FM is immune to noise.
(b) AM has only two sidebands while FM has more.
(c) FM uses larger bandwidth for large modulation depth.
(d) Capture effect appears in FM.
Answer : (a) FM is immune to noise.
148. Major advantage of Armstrong modulator is that
(a) it is capable of producing WBFM signals.
(b) the centre frequency (carrier frequency when unmodulated) is extremely stable.
(c) a large depth of modulation can be achieved.
(d) None of these.
Answer : (a) it is capable of producing WBFM signals.
149. Which one of the following statements is correct ?
One hundred percent modulation of the carrier for the broadcast FM radio band is achieved when
(a) carrier frequency changes by ±100%.
(b) carrier envelope changes by ±100%.
(c) carrier frequency changes by ±75%.
(d) carrier frequency changes by ±15 kHz.
Answer : (a) carrier frequency changes by ±100%.