Bharat Electronics Technical-Electronics Contributed by Thushar updated on Jun 2020
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BEL Placement Paper

Technical - Electronics

1. For a RC high pass circuit
1. RC < < t
2. RC > > t
3. RC = t
4. None

2. An inverter is an equipment for transforming
1. AC to DC
2. AC to AC
3. DC to DC
4. DC to AC

3. Suppose you wish to amplify the potential difference between two points in a circuit when neither of these points is grounded. Which one the following will you prefer?
1. RC coupled amplifier
2. Transformer coupled amplifier
3. Difference amplifier
4. Direct coupled amplifier

4. In an emitter follower, the output voltage is
1. 180o out of phase from the input voltage
2. 90o out of phase from the input voltage
3. in phase with the input voltage
4. None

5. A silicon controlled rectifier can be considered to be:
1. Two pnp transistor connected back to back
2. Two npn transistor connected back to back
3. One npn and one pnp transistor connected back to back
4. Two zener diodes connected back to back

6. A rf signal contains three frequency components 870 KHz, 875 KHz 880 KHz. This signal needs to be amplified. The amplifier used should be
1. Audio frequency amplifier
2. Wide band amplifier
3. Push pull amplifier
4. None

7. In the emitter follower circuit
1. The output current and voltage are inphase with the input current and voltage respectively
2. The input and output impedances are equal
3. There is current series negative feedback
4. The output impedance is much higher than the input impedance

8. The frequency response of a system is the range of frequencies between the upper and lower
1. 1 dB points
2. 6 dB points
3. 3 dB points
4. None

9. In a class C amplifier the output current is zero for
1. Half cycle
2. Full cycle
3. Less than half cycle
4. More than half cycle

10. When RL [load resistance] equals the internal resistance of a generator, which of the following is maximum:
1. Power in RL
2. Current through RL
3. Voltage across RL
4. Efficiency of the circuit

11. negative feedback in an amplifier results in:
1. increased gain and increased bandwidth
2. increased gain and reduced bandwidth
3. reduced gain and increased bandwidth
4. reduced gain and reduced bandwidth

12. A class B push-pull amplifier suffers from
1. Cross-over distortion
2. Excessive harmonic distortion
3. Inter modulation distortion
4. None

13. An oscillator of the LC type that has split capacitor in the tank circuit is
1. Hartely oscillator
2. Wein bridge oscillator
3. Colpitts oscillator
4. None

14. Clamping circuits are also known as
1. AC restorer
2. DC restorer
3. Voltage to frequency converter
4. None

15. Which of the following has the greater mobility
1. Positive ion
2. Negative ion
3. Electrons
4. Holes

16. An N type semiconductor as a whole is
1. Positively charged
2. Electrically neutral
3. Negatively charged
4. None

17. In a semiconductor, the forbidden energy gap is of the order
1. 1 ev
2. 6 ev
3. 7 ev
4. 0.1 ev

18. In LED, light is emitted because
1. Recombination of charges take place
2. We make the light fall on LED
3. Diode emits light when heated
4. None

19. UJT is also called
1. A voltage controlled device
2. A current controlled device
3. A relaxation oscillator
4. None

20. The transistor configuration which provides higher output impedance is
1. CC
2. CB
3. CE
4. None

21. Tunnel diodes are fabricated from
1. Silicon
2. Germanium
3. Either silicon or germanium
4. Either germanium or gallium

22. N channel FETs are superior to P channel FETs because
1. They have a higher input impedance
2. They have a high switching time
3. They consume less power
4. Mobility of electrons is greater than that of holes

23. Diac is a solid state device which works as a
1. 2 terminal bidirectional switch
2. 2 terminal unilateral switch
3. 3 terminal bidirectional switch
4. None

24. Triac is a solid device which works as a
1. 2 terminal bidirectional switch
2. 3 terminal bidirectional switch
3. 4 terminal bidirectional switch
4. 2 terminal unilateral switch

25. Compared to a CB amplifier, a CE amplifier has
1. Lower input resistance
2. Higher output resistance
3. Lower current amplification
4. Higher current amplification

26. The input and output signals of a common emitter amplifier are:
1. Always equal
2. Out of phase
3. In phase
4. Always negative

27. The operation of a JEET involves
1. A flow of minority carriers
2. A flow of majority carriers
3. Recombination
4. Negative resistance

28. Solar cell is an example of a
1. Photo conductive device
2. Photo emissive device
3. Photo voltage device
4. None

29. Bretters and bolometers are used in the measurement of
1. Microwave power
2. VSWR
3. Transmission losses
4. None

30. A klystron operates on the principle of
1. Velocity modulation
2. Amplitude modulation
3. Pulse modulation
4. Frequency modulation

31. The unit of the amplification factor of a triode is
1. Decibels
2. Volt
3. Neper
4. None

32. A change in base current from 30 to 40 mA changes the collector current from 500 to 900 mA. The B factor for this power transistor equals
1. 900
2. 500
3. 3
4. 40

33. The field effect transistor can be used as
1. Variable capacitance
2. A constant voltage source
3. A variable resistance
4. A constant current source

34. Why NPN transistor are preferred over PNP transistor
1. NPN transistor have low heat dissipation
2. NPN transistor can handle large power
3. NPN transistor are cheap and easily available
4. None

35. The germanium transistors are seldom used above
1. 60oC
2. 75oC
3. 125oC
4. 175oC

36. In a FET the drain voltage above which there is no increase in the drain current is called
1. Pick off voltage
2. Critical voltage
3. Pinch off voltage
4. Break down voltage

37. A reflex klystron has
1. Only one cavity working both as the buncher & the catcher
2. Two cavities one for buncher and one for the catcher
3. Three cavities, two for buncher and one for catcher
4. No cavity at all

38. Bipolar junction transistors are seldom used as switching devices because
1. BJTs are not economical fro using as switching devices
2. They can handle only high voltage but not high currents
3. They need separate circuits when used as switching device
4. Of slow response and inability to withstand high voltage

39. The voltage at which the electron flow starts from the anode is called
1. Break down voltage
2. Peak inverse voltage
3. Peak voltage
4. Pinch off voltage

40. The heater filament of a vacuum tube is generally supplied with AC voltage (and not DC voltage) for heating because
1. It results in a uniform heating of filament so that the electron emission also uniform
2. It is very easy to obtain AC voltage from AC power mains
3. The DC voltage that would be required for heating has much greater magnitude than the AC voltage
4. When DC is used for heating, a different type of filament is required which very expensive

41. The dopant used for P type semiconductor is
1. Phosphorous
2. Boron
3. Carbon
4. Sodium

42. An example of negative resistance characteristic device
1. BJT
2. MOSFET
3. UJT
4. PINdiode

43. The average DC voltage obtained from a bridge rectifier with a sine wave input V sin wt is
1. V / 2
2. 2V
3. 4V
4. V

44. The maximum theoretical efficiency of a class B amplifier is
4. 100%

1. A CE amplifier followed by CC amplifier
2. A CE amplifier followed by CB amplifier
3. A CC amplifier followed by CB amplifier
4. A CB amplifier followed by CE amplifier

46. Toggle switches can be debounced using
1. Astable multivibrator
2. Shift register
3. RS flip flop
4. None

47. A band pass filter has a centre frequency at 5 KHz. The 3 dB cut off frequencies are 4.5 KHz and 5.5 KHz. The Q factor of the filter is
1. 5
2. 0.2
3. 5.2
4. 0.45

48. The domestic buzzer makes use of
1. Hall effect
2. Tunneling effect
3. Natural resonance
4. Piezoelectric effect

49. The device which uses avalanche breakdown is
1. PIN diode
2. Zener diode
3. Impart diode
4. GUNN diode

50. The correct relation between Alpha and Beta of a transistor is
1. a / b-1
2.b=a-1
3. b = a / 1-a
4. a = b + 1/ b