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MCQs on Analog Electronics

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01․ The feedback factor of a Wien bridge oscillator using Op-Amp is
1/3
1/4
1/2
1

At the resonant frequency, the feedback factor (R2/R1) of a Wien bridge oscillator using Op-Amp, is 1/2. Hence, the amplifier gain must be greater than 2 to maintain sustained oscillations.
02․ For audio frequency applications, the popular oscillator used is
Wien bridge oscillator
Hartley oscillator
Crystal oscillator
Phase shift oscillator

Characteristics like ease of tuning, very low distortion and good frequency stability of Wien bridge oscillator makes it becomes popular for audio frequency applications. Phase shift oscillator and Wien bridge oscillator both can be used as audio frequency range. But Wien bridge oscillator can be used for very wide frequency range.
03․ Colpitts oscillator is also called as
Tank circuit oscillator
LC oscillator
Resonant circuit oscillator
All of the above

Colpitts oscillator is one of the type of LC oscillator which consisting of resonant tank circuit. The tank circuit consists of two series capacitor parallel with a inductor. Therefore, we can call any of the names mentioned above.
04․ A quartz crystal oscillator consists of
only series resonant frequency.
only parallel resonant frequency.
both series and parallel frequencies.
neither series nor parallel frequency.

Crystal Oscillator has two closely spaced resonant frequency. In crystal oscillator, series resonant frequency occurs when reactance of the capacitor is equal to the reactance of the inductor (low impedance). Parallel resonant frequency occurs when reactance of the capacitor C2 is equal to the reactance of RLC1 branch (High impedance).
05․ Which oscillators are easy to fabricate in a monolithic IC?
Crystal oscillator.
Hartley oscillator.
Wien bridge oscillator.
Relaxation oscillator.

Relaxation oscillators do not use inductor and its output depends on nonlinear characteristics of the circuit. Therefore, a relaxation can be easily fabricated in a monolithic IC's.
06․ Which of the following is not a sinusoidal oscillator?
LC oscillator
RC phase shift oscillator
Relaxation oscillator
Crystal oscillator

Relaxation oscillator is basically a non-sinusoidal oscillator which is used to generate square, triangular or pulse waveforms. The rest of the oscillators are sinusoidal oscillators producing sinusoidal output.
07․ Voltage controlled oscillators are used commonly in
Pulse Modulators Frequency Modulators Phase Clocked loops
Frequency Modulators
Phase Clocked loops
All the above

VCOs are commonly used in electronic jamming equipment, function generator, for production of different types of noise, phase locked loop, frequency synthesizers or modulators used in communication circuits etc.
08․ One of the following is the primary function of an oscillator
produces sinusoidal oscillations
generates non sinusoidal waveforms
generates sustained oscillations at a constant amplitude and specific frequency
none of the above

The oscillating nature of a circuit make it as oscillator. But to produce sustained oscillations in a controllable and desired manner and has to satisfy Bark-hausen criterion.
09․ Relaxation Voltage controlled oscillators are used to generate
Sinusoidal wave
Triangular wave
Sawtooth wave
Both B and C

Relaxation VCOs can be employed to generate both triangular and saw-tooth waveforms.
10․ Feedback circuit in an oscillator can be accomplished by
Resistive coupling between input and output
Capacitive coupling between input and output
Inductive coupling between input and output
Any one or combinations of the above methods

For different type of applications, oscillators can be built with different feedback circuit to produce proper phase and amplitude. These types of oscillators include RC and LC oscillators. Colpitts oscillators uses capacitive feedback, Hartley oscillator uses inductive feedback.
11․ The following are the necessary requirements of an oscillator
Amplitude stability
Frequency stability
Power stability
Both A and B

The amplitude and frequency stabilities are the primary requirements for the oscillator which determines the ability to maintain constant amplitude, sustained oscillation and desired frequency of the output waveform.
12․ The Barkhausen criterion for an oscillator
Loop gain should be unity
Loop gain should be less than unity
The phase of a feedback signal with respect to input should be 0° or 360°
Both A and C

Amplitude of oscillations is decided by unity loop gain and frequency of oscillations is controlled by phase angle. To get sustained oscillation both conditions have to be met. .
13․ LC oscillators are used for produce a waveform with frequency ranging from
1MHz to 500 MHz
100 KHz to 500 MHz
1 KHz to 1 MHz
1MHz to 100 GHz

LC oscillators are used to produce the output at frequency ranging from 1 MHz to 500MHz that’s why these are also called as RF (radio frequency) oscillators.
14․ Which of the following oscillators are used for low frequency (LF) applications
LC oscillators
RC oscillators
Both LC and RC Oscillators
None

RC oscillators are used for LF applications because an LC oscillator is difficult to be realized at low frequencies as the size of the inductor required is very large, expensive and bulky.
15․ The expression for frequency of oscillations of a RC phase shift oscillator is
f = 1 / (2π√RC)
f = 1 / (2π√R(C1 + C2))
f = 1 / (2π RC√6)
none of the above

The frequency oscillations of RC phase shift oscillator is as it contains three RC sections.
16․ A diode (P-N junction) has two terminals. The P-terminal is known as
Anode
Cathode
Either anode or cathode
None of these

A diode is a semiconductor device which is formed by combining the P-type material and N-type material to diffuse together. P-type material has holes as majority carriers while N-type material has electrons as majority carriers. So, the P-type side is anode and N-type side is cathode.
17․ A working diode must have
High resistance when forward or reverse biased
Low resistance when forward biased, while high resistance when reverse bias
High resistance when forward biased, while low resistance when reverse bias
Low resistance when forward or reverse biased

A working diode means the diode is biased or connected with the DC source. When a diode is forward biased ( +ve terminal to anode and -ve terminal to cathode ), it provides a low resistance path because it helps the majority carrier to crossover the barrier potential and conduct the flow of current. When a diode is reversed biased ( -ve terminal to anode and +ve terminal to cathode ) it provide a high resistance path because the majority carriers are flows away from the junction and no current conduction takes place.
18․ Electrons in p-type material of a semi-conductor are called as
either minority carriers or majority carriers
minority carriers
majority carriers
valance carriers

Electrons in p-type and n-type material of a semi-conductor are called as minority charge carriers and majority charge carriers respectively. Electrons are less in number in the p-type as compared to the holes present in it. So, it is a minority carriers in p-type material.
19․ Silicon and Germanium are ________ elements.
trivalant
pentavalant
hexavalant
tetravalant

Silicon and Germanium belong to group IVa of the periodic table consisting of four electrons in their valance shell, also called as tetravalant elements. Group IVa elements are Carbon (C) (6) Silicon (Si) (14) (2 8 4) Germanium (Ge) (32) (2 8 18 4) Tin (Sn) (50) Lead (Pb) (82)
20․ A diode (p-n junction) when reverse biased act as
On Switch
Zener diode
Capacitor
Off Switch

A diode when reverse biased (positive terminal of the battery is connected to cathode and negative terminal of the battery is connected to anode) does not conduct any considerable electric current and hence acts as an off switch.
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