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BEL PE Question Paper for Electronics - 2

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BEL Question Paper for Electronics 

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Thyristor A has rated gate current of 2A and thyristor B a rated gate current of 100 mA
a) A is a GTO and B is a conventional SCR
b) B is a GTO and A is a conventional SCR
c) B may operate as a transistor
d) none of the above
Answer: a)

In a 3 phase full converter, the output voltage during overlap is equal to
a) zero
b) source voltage
c) source voltage minus the inductance drop
d) average value of the conducting phase voltages
Answer: d)

Mark old the correct statement for CycloConverters
a) step-down CycloConverter (CC) works on natural commutation
b) step up CC requires no forced commutation
c) load commutated CC works on line commutation
d) none of the above
Answer: a)

In a 3 phase full converter if load current is I and ripple free, then average thyristor current is
Answer: 1/3(I)

In the RF amplifier stage cascade (CE-CB) amplifier is used because it gives
a) Large voltage gain
b) Low output impedance
c) Large isolation between the input and the output
d) None of the above
Answer: c)

Silicon diode is less suited for low voltage rectifier operation because                            
a)it can withstand high temperature
b) ensures low PIV of the diodes
c) ensures lower values of capacitance in the filter
d) reduces ripple content
Answer: a)

An amplifier of class A is that in which –
a) Base is biased to cut ? off
b) Ic flows most of the time
c) Ie flows all the time
d) Vc often raises to Vcc
Answer: c)

A transistor is in active region when
a) IB = bIC
b) IC=bIB
c) IC=IE
d) IC=IB
Answer: a)

For coupling purposes in RF amplifier a buffer amplifier is used because it provides
a) Maximum loading and minimum mismatch
b) Minimum loading and minimum mismatch
c) Maximum loading and maximum mismatch
d) Minimum loading and maximum mismatch
Answer: b)

A transistor has CE parameter as hie = 10kW, hre =20 x 10-4 , hse = 100, hoe = 25 ms. The hib for this transistor will be
a) 100 W
b) 99.01 W
c) 5m W
d) 101Kw
Answer: b)

An FM radio receiver is tuned to a 90.6 MHz broadcast station. It will receive an image frequency of -
a) 110 MHz
b) 112 Hz
c) 114 MHz
d) 120 MHz
Answer: b)

In the given fig RL is shorted out, then VCE will become
a) OV
c) Equal to VCC
d) None of the above
Answer c)

See the circuit shown and choose the correct option ?
a) Only red will glow
b) Only green will glow
c) Both red and green will glow
d) Neither red nor green will glow
Answer: a)

A dc to dc converter having an efficiency of 80% is delivering 16W to a load) If the converter is generating an output of 200V from an input source of 20V, then the current drawn from the source will be ?
a) 0.1A
b) 0.5A
c) 1.0A
d) 10.0A
Answer: c)

A transistor is operated as a non-saturated switch to eliminate ?
a) storage time
b) turn ? off time
c) turn ? on time
d) delay time
Answer: b)

The output Y of the circuit in the given figure is ?
a) (A + B)C + DE
b) AB + C(D + E)
c) (A + B)C + D + E
d) (AB + C) . DE
Answer: a)

Rotors used in a two-phase ac servomotor is ?
a) solid iron motor
b) squirrel cage rotor
c) drag cup rotor
d) both b and c
Answer: d)

When a piece of copper and another of germanium are cooled from room temperature to 800 K then the resistance of -
a) Each of them increases
b) Each of them decreases
c) Copper increases and germanium decreases
d) Copper decreases and germanium increases
Answer: d)

When a signal of 10 mV at 75 MHz is to be measured then which of the following instrument can be used -
b) Cathode ray oscilloscope
c) Moving iron voltmeter
d) Digital multimeter
Answer: b)

When a sample of germanium and silicon having same impurity density are kept at room temperature then ?
a) Both will have equal value of resistivity
b) Both will have equal value negative resistivity
c) Resistivity of germanium will be higher than that of silicon
d) Resistivity of silicon will be higher than that of germanium
Answer: d)
When an RC driving point impedance function has zeros at s= -2 and s=-5 then the admissible poles for the function would be ?
a) s = 0; s = -6
b) s = 0; s = -3
c) s = 0; s = -1
d) s = -3; s = -4
Answer: b)
For the n-type semiconductor with n = Np and p = , the hole concentration will fall below the intrinsic value because some of the holes ?
a) drop back to acceptor impurity states
b) drop to donor impurity states
c) Virtually leave the crystal
d) recombine with the electrons
Answer: d)
The location of lighting arrestor is ?
a) Near the transformer
b) Near the circuit breaker
c) Away from the transformer
d) None
Time constant of an RC circuit increases if the value of the resistance is ?
a) Increased
b) Decreased
c) Neither a nor b
d) Both a and b
Answer: a)
Telemetering is a method of ?
a) Counting pulses sent over long distances
b) Transmitting pictures from one place to another
c) Transmitting information concerning a process over a distance
d) None
Answer: c)
When the gauge factor of a strain gauge is 2, stress is 1050 kg/cm2, Y = 2.1? 106 kg/cm2 and R is 100 ohms then the value of DR will be -
a) 2W
b) 3W
c) 4W
d) 1W
Answer: d)
As the drain voltage is increased for a junction FET in the pinch off region then the drain current ?
a) Becomes zero
b) Abruptly decreases
c) Abruptly increases
d) Remains constant
Answer: d)
One of the following, which is not a transducer in the true sense, is ?
a) Thermocouple
b) Piezoelectric pick up
c) Photo-Voltaic cell
d) LCD
Answer: d)
When a transistor is required to match a 100W signal source with a high impedance output circuit then the connection that would be used is ?

a) Common base
b) Common collector
c) Common emitter
d) Emitter follower
Answer: a)
In a JFET gates are always ?
a) forward biased
b) reverse biased
c) unbiased
d) none
Answer: c)
The main factor which differentiate a DE MOSFET from an E only MOSFET is the absence of ?
a) insulated gate
b) electrons
c) channel
d) P-N junction
An SCR conducts appreciable current when ?
a) Anode and gate are both negative with respect to cathode
b) Anode and gate are both positive with respect to cathode
c) Anode is negative and gate is positive with respect to cathode
d) Gate is negative and anode is positive with respect to cathode
Silicon is not suitable for fabrication of light emitting diodes because it is -
a) An indirect band gap semiconductor
b) A direct band gap semiconductor
c) A wide band gap semiconductor
d) A narrow band gap semiconductor
An average responding rectifier type electronic ac voltmeter has its scale calibrated in terms of the rms value of a sine wave, when a square wave voltage of peak magnitude 100V is measured using this voltmeter then the reading indicated by the meter, will be ?
a) 111V
b) 100V
c) 90.09V
d) 70.7V
Answer: b)
When a four terminal T network is inserted between a source and load resistance as shown in figure then the resistance seen by the source remain the same with or without the four terminal block when R is ?

a) 5W
b) 10 W
c) 15 W
d) 20 W
Answer: a)
In the ac bridge shown in the given figure, the value of Rx and Cx at balance will be
Which one of the following conditions for Z parameters would hold for a two port network containing linear bilateral passive circuit elements ?
a) Z11 = Z22
b) Z12Z21 = Z11Z22
c) Z11Z12 = Z22Z21
d) Z12 = Z21
Answer: d)
While calculating Rth, constant current sources in the circuit are ?
a) replaced by opens
b) replaced by ?shorts?
c) treated in parallel with other voltage sources
d) converted into equivalent voltage sources
Answer: a)

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