# Recent questions and answers in Amplifier

If the feedback factor of an amplifier is 0.1 and its gain without feedback is 40, then its gain with feedback is (a) – 13.3 (b) 200 (c) 8 (d) 10

The unity gain bandwidth of an inverting amplifier is 10 MHz What would be the bandwidth if the gain is increased to 10 V/V? A) 100 MHz B) 1 MHz C) 10 MHz D) 1 kHz

When the initial slope of input sine wave is greater than the slew rate of an OPAMP, the output: (1) Has no offset (2) Approaches to triangular waveshape (3) Is pure sinusoidal (4) Is square wave

The ideal operational amplifier does not have: (1) Infinite input resistance (2) Infinite output resistance (3) Infinite voltage gain (4) Infinite bandwidth

An amplifier without feedback has a voltage gain of 50, input resistance 1kΩ and output resistance of 2.5kΩ. The input resistance of the current-shunt negative feedback amplifier using the above amplifier with a feedback factor of 0.2 would be: (1) 1/11 kΩ (2) 1/5 kΩ (3) 5 kΩ (4) 11 kΩ

The gain of an FET amplifier can be changed by changing: (1) rm (2) gm (3) Rd (4) None of these

The amplifier having the highest amount of distortion is (a) Class A (b) Class B (c) Class C (d) Class AB

If the emitter resistance ‘Re ’ in a transistor amplifier is removed, then (a) base to emitter junction will be less forward biased. (b) gain of amplifier decreases. (c) Q-point becomes unstable. (d) All of these

A high-Q tuned circuit in an amplifier permits to have high (a) selectivity (b) fidelity (c) sensitivity (d) frequency ranges

Push-pull amplifier circuit is used as (a) RF amplifier (b) audio amplifier (c) power amplifier (d) current amplifier

A low noise amplifier has an effective noise temperature of 50 k. The absolute noise figure is

An amplifier operating over the frequency range from 18 to 20 MHz has 10 kilo ohm input resistor. What is the r.m.s. noise voltage at the input to this amplifier if the ambient temperature is 27o C

For a feedback amplifier, if the loop gain is much greater than unity, the closed loop gain will be equal to

For Cascode amplifier the output impedance becomes

Negative feed back:

An amplifier without feedback has a gain of 1000. The gain with a negative feedback of 0.009 is  A) 10 B) 100 C) 125 D) 900

An operational amplifier has an open loop gain of 200,000. Its output exhibits saturation at 10V. The threshold differential voltage of the amplifier is  A) 25 micro-volt B) 50 micro-volt C) 5 Volts D) 10 volts

The amplifiers following the modulated stage in a low level modulation AM system be  (A) linear amplifier (B) harmonic generators (C) class C power amplifiers (D) class untuned amplifiers

In a radio receiver the IF amplifier  (A) is tuned above the stations incoming frequency (B) amplifies the output of local oscillator (C) is fixed tuned to one particular frequency (D) can be tuned to various isolate frequencies

Class A amplifier is used when  (A) No phase inversion is required (B) Highest voltage gain is required (C) dc voltages are to be amplified (D) Minimum distortion is desired.

Negative feedback amplifier has a signal corrupted by noise as its input. The amplifier will   (A) Amplify the noise as much as the signal (B) Reduce the noise (C) Increase the noise (D) Not effect the noise

In an IF amplifier, the IF transformer is provided with tapping to  (a) increase the voltage gain (b) increase the bandwidth of the resonance circuit (c) increase the impedance offered by the resonance circuit to the following cascaded amplifier (d) increase the quality factor of the resonance circuit

In a Klystron amplifier, the RF voltage produces  (a) amplitude modulation (b) frequency modulation (c) phase modulation (d) velocity modulation

In class - A power amplifier, the collector dissipation is maximum when  (a) no signal is present  (b) signal swing is maximum  (c) signal swing is (1/1.414) of its maximum  (d) none of the above

In Class ‘B’ amplifier, the output current flows for

An Op-amp as a voltage follower has a voltage gain of

The efficiency of a class B push-pull amplifier is

The transistor configuration to connect 4 W speaker with 600 W output impedance audio amplifier is • Common Emitter • Common Base • Common Collector • None of the above.

Which of the following amplifier has the least distortion. • Class E • Class D • Class C • Class A

The battery operated pre-amplifier with a consumption of 10 Watts can work on battery of 12 volt, 100 AH having efficiency of 50% for • 120 hrs. • 60 hrs. • 100 hrs. • 10 hrs.

The input impedance of an op-amp is • High • Low • Medium • None of the above

An OP-AMP can be classified as  1.Linear amplifier 2.Low - Rin amplifier 3.Positive - feedback amplifier 4.RC - coupled amplifier

In class-A amplifier conduction extends over 360° because the operating point.  1. Located near saturation point 2. Located at or near cut-off point 3. Located on load line 4. Located in the centre of load line

The voltage gain of a common base amplifier depends on  1. Load resistor RL 2. input resistance of transistor 3. Ac alpha 4. All the above

Cross over distortion in class - B push-p amplifiers:  1. Is due to transistor operating near saturation region  2. Can be eliminated by operating them in class operation  3. Occurs because two power transistors do not exactly matching parameters  4. Always occurs in low signal area

Just as a voltage amplifier signal voltage a power amplifier.  1.amplifier power  2.amplifier signal  3.converts the signal ac power into DC power  4.converts a dc power into useful AC power

Harmonic distortion of the signal is produced in an RC coupled transistor amplifier. The probable component responsible for this distortion is  (A) The transistor itself  (B) the power supply Vcc  (C) the coupling capacitor Cc  (D) the biasing resistors

The main component responsible for the fall of gain of an RC coupled amplifier in low frequency range is  (A) The active device itself (tube, or transistor)  (B) stray shunt capacitance Cs  (C) the grid leak resistance Rg  (D) coupling capacitor Cc

The main function of the transformer used in the output of a power amplifier is  (A) To step up the voltage  (B) to increase the voltage gain  (C) to safeguard the transistor against overheating  (D) to match the load impedance with dynamic output resistance of the transistor

Negative feedback in an amplifier is accompanied by (A) Gain less sensitive to component variations (B) Increase in gain (C) Decrease in bandwidth (D) None of the above