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BSNL electronics and electrical questions with answer
1. 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 (Ans)
2. 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) 2 W
(B) 3 W
(C) 4 W
(D) 1 W (Ans)
3. 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 (Ans)
(D) None
4. Time constant of an RC ciruit increases if the value of the resistance is
(A) Increased (Ans)
(B) Decreased
(C) Neither a nor b
(D) Both (A) and (B)
5. The location of lighting arrestor is
(A) Near the transformer (Ans)
(B) Near the circuit breaker
(C) Away from the transformer
(D) None
6. For the n-type semiconductor with n = NP and P = p2/ND 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 (Ans)
7. 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 (Ans)
(C) s = 0 ; s = -1
(D) s = 0 ; s = -4
8. 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 (Ans)
9. When a signal of 10 mV at 75 MHz is to be measured then which of the following instrument can be used
(A) VTVM
(B) Cathode ray oscilloscope (Ans)
(C) Moving iron voltmeter
(D) Digital multimeter
10. When a piece of copper and another of germanium are cooled from room temperature to 8000 K then the resistance of
(A) Each of them increases
(B) Each of them decrease
(C) Copper increases and germanium decreases
(D) Copper decreases and germanium increases (Ans)
11. 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 (Ans)
12. When a transistor is required to match a 100 W signal source with a high impedance output circuit then the connection that would be used is
(A) Common base (Ans)
(B) Common collector
(C) Common emitter
(D) Emitter follower
13. In a JFET gates are always __
(A) forward biased
(B) reverse biased (Ans)
(C) unbiased
(D) none
14. The main factor which differentiate a DE MOSFET from an E only MOSFET is the absence of ___
(A) insulated gate
(B) electrons
(C) channel (Ans)
(D) P-N junction
15. 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 (Ans)
(C) Anode is negative and gate is positive with respect to cathode
(D) Gate is negative and anode is positive with respect to cathode
16. 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 (Ans)
(C) A wide band gap semiconductor
(D) A narrow band gap semiconductor
17. 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 100 V is measured using this voltmeter then the reading indicated by the meter, will be
(A) 111 V (Ans)
(B) 100 V
(C) 90.09 V
(D) 70.7 V
18. 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) Z12 Z21 = Z11 Z22
(C) Z11 Z12 = Z22 Z21
(D) Z12 = Z21 (Ans)
19. The number of lobes on each side of a 3 resonant antenna is
(A) 3
(B) 6 (Ans)
(C) 2
(D) 1
20. A yagi antenna has a driven antenna-
(A) Only
(B) With a reflector
(C) With one or more directors
(D) With a reflector and one or more directors (Ans)
21. For an elliptically polarized wave incident on the interface of a dielectric at the Brewster angle then the reflected wave will be
(A) Elliptically polarized
(B) Linearly polarized (Ans)
(C) Right circularly polarized
(D) Left circularly polarized
22. A transmission line of characteristic impedance Z0 = 50 ohms, phase velocity VP = 2 * 108 m/s at = 1 m is terminated by a load ZL = (30 –j40) ohms. The input impedance of the line for a frequency of 100 MHz will be
(A) (30 + j40) ohms
(B) (30 – j40) ohms (Ans)
(C) (50 + j40) ohms
(D) (50 – j40) ohms
23. Maxwell’s loop current method of solving electrical networks
(A) uses branch currents
(B) utilizes Kirchhoff’s voltage law (Ans)
(C) is confined to single-loop circuits
(D) is a network reduction method.
24. While calculating Rth, constant current sources in the circuit are
(A) replaced by opens (Ans)
(B) replaced by ‘shorts’
(C) treated in parallel with other voltage sources
(D) converted into equivalent voltage sources
25. In the circuit shown, the switch closes at t = 0. The voltage across 4µF capacitor in ideal condition
(A) 0
(B) 16 V (Ans)
(C) 15 V
(D) 24 V
26. Radiation resistance of a half wave folded dipole is
(A) 72 Ω
(B) 144 Ω
(C) 288 Ω (Ans)
(D) 216 Ω
27. When a carrier wave is modulated at 100% it’s power is increased by
(A) 100%
(B) 15%
(C) 50% (Ans)
(D) 0%
28. On a clear sky day, the atmospheric ratio noise is strongest
(A) During morning house
(B) Around mid-day
(C) During nights (Ans)
(D) In the afternoon.
29. TV broadcasting system in India is as per CCIR
(A) System B (Ans)
(B) System I
(C) System M
(D) System X
30. For the safety measurement of the internal resistance of a 25-0-25 µA meter, a laboratory multimeter whose sensitivity is equal to _.
(A) 1 k ohm/volt can be used
(B) 10 k ohm/volt can be used
(C) 100 k ohm/volt can be used
(D) 200 k ohm/volt can be used (Ans)
31. In order to measure moisture in wood the most suitable method is
(A) Electrical conduction (Ans)
(B) Electrical-capacitive
(C) Absorption of radiation
(D) Equilibrium-moisture vs humidity
32. The flow rate of electrically conducting liquid without any suspended particle cannot be measured by
(A) turbine flow meters
(B) electromagnetic flow meters
(C) ultrasonic flow meters
(D) thermistor based heat loss flow meters (Ans)
33. The most useful transducer for displacement sensing with excellent sensitivity, linearity and resolution is
(A) an incremental encoder
(B) an absolute encoder
(C) LVDT (Ans)
(D) a strain gauge
34. When variable reluctance type techometer has 150 teeth on the rotor and the counter records 13,500 pulses per second then the rotational speed will be
(A) 4800 rpm
(B) 5400 rpm (Ans)
(C) 6000 rpm
(D) 7200 rpm
35. 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 (Ans)
(D) None of the above
36. Silicon diode is less suited for low voltage rectifier operation because
(A) it can withstand high temperature (Ans)
(B) ensures low PIV of the diodes
(C) ensures lower values of capacitance in the filter
(D) reduces ripple content
37. An amplifier of class A is that in which
(A) Base is biased to cut – off
(B) Ie flows most of the time
(C) Ie flows all the time (Ans)
(D) Vc often raises to Vcc
38. A transistor is in active region when
(A) IB = b IC
(B) IC = b IB (Ans)
(C) IC = IE
(D) IC = IB
39. 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 (Ans)
(C) Maximum loading and maximum mismatch
(D) Minimum loading and maximum mismatch
40. A transistor has CE parameter as hje = 10k Ω, hre = 20 * 10-4, hse= 100, hoe = 25 µs. The hib for this transistor will be
(A) 100 W
(B) 99.01 W (Ans)
(C) 5m W
(D) 101 kW
41. 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 (Ans)
(C) 114 MHz
(D) 120 MHz
42. If RL is shorted out, then VCE will become
(A) OV
(B) VCC – IBRB
(C) Equal to VCC (Ans)
(D) None of the above
43. A dc to dc converter having an efficiency of 80% is delivering 16W to a load. If the converter is generating an output of 200 V from an input source of 20 V, then the current drawn from the source will be
(A) 0.1 A
(B) 0.5 A
(C) 1.0 A (Ans)
(D) 10.0 A
44. On a voltage scale, zero dB m in a 600-ohm system could refer to
(A) 1.732 V
(B) 1.0 V (Ans)
(C) 0.7746 V
(D) 0.5 V
45. One of the following devices which is required in addition in order to measure pressure using LVD is
(A) Strain gauge
(B) Pitot tube
(C) Bourden tube (Ans)
(D) Rotameter.
46. It is required to measure temperature in the range of 13000 C to 15000 C. The most suitable thermocouple to be used as a transducer would be
(A) chromel-constantan
(B) Iron-constantan
(C) chromel – alumel
(D) platinum – rhodium (Ans)
47. In a CSI if frequency of output voltage is fHz, then frequency of input voltage to CSI is-
(A) f
(B) 2f (Ans)
(C) f/2
(D) 3f
48. Identify the type of chipper in the given circuit
(A) Type A chopper
(B) Type B chopper (Ans)
(C) Type C chopper
(D) Type D chopper
49. Maximum value of charging resistance in an UJT associated with-
(A) peak point (Ans)
(B) valley point
(C) any point between peak and valley
(D) after the valley point
50. 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 (Ans)