Electronics

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1)   The use of crystal in a tunable oscillator

  • [A] Helps to obtain optimum output impedance
  • [B] Facilitates generation of wide range of frequencies
  • [C] Increases the gain of the oscillator
  • [D] Improves frequency stability

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Improves frequency stability
Piezoelectric crystal is used as a resonant tank circuit. The crystal is made of quartz material and provides a high degree of frequency stability

2)   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 increased and Ro is decreased
  • [B] Both Ri and Ro are increased
  • [C] Both Ri and Ro are decreased.
  • [D] Ri is decreased and Ro increased

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Both Ri and Ro are decreased.

3)   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] 20
  • [B] 30
  • [C] 10
  • [D] 15

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20

Resistance at any point in the forward characteristics is given by R= V/ I = 1/50mA = 20

4)   n-type silicon is obtained by

  • [A] Doping with tetravalent element
  • [B] Doping with a mixture of trivalent and tetravalent element
  • [C] Doping with pentavalent element
  • [D] Doping with trivalent element

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Doping with pentavalent element
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.

5)   In a bistable multivibrator circuit, commutating capacitor is used

  • [A] to increase the base storage charge
  • [B] to provide the speed of oscillations
  • [C] to provide ac coupling
  • [D] to increase the speed of response

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to increase the speed of response

The commutating capacitor is used for the speedy transition of the state of the bistable.

6)   The function of a bleeder resistor in a power supply is

  • [A] to increase the output current
  • [B] to ensure a minimum current drain in the circuit
  • [C] to increase the output dc voltage
  • [D] the same as that of load resistor

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to ensure a minimum current drain in the circuit

7)   An oscillator of the LC type that has a split capacitor in the circuit is

  • [A] Colpitts oscillator
  • [B] Hartley oscillator
  • [C] R-C phase shift oscillator
  • [D] Weinbridge oscillator

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Colpitts oscillator

 We have two capacitors in the tank circuit, which serve as a simple ac voltage divider.

8)   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] wide band amplifier
  • [B] push-pull amplifier
  • [C] audio frequency amplifier
  • [D] tuned voltage amplifier

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tuned voltage amplifier
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.

9)   Just as a voltage amplifier amplifies signal-voltage, a power amplifier

  • [A] Amplifies signal current
  • [B] Merely converts the signal ac power into the dc power
  • [C] Merely converts the dc power into useful ac power
  • [D] Amplifies power

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Merely converts the dc power into useful ac power

10)   The upper cutoff frequency of an RC coupled amplifier mainly depends upon

  • [A] Coupling capacitor
  • [B] Emitter bypass capacitor
  • [C] Inter-electrode capacitance and stray shunt capacitance
  • [D] Output capacitance of signal source

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Inter-electrode capacitance and stray shunt capacitance

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