BHEL supervisor trainee question paper :Electronics
BHEL Model Question Paper For Trainee Jobs : electronics
Electronics Objective MCQ test BHEL Engineer and Supervisor Trainee Exam Question Paper
1. The main deference between PN-junction diode and Schottky diode is that the recovered charge of
(a) PN-junction diode is less than that of Schotty diode and the leakage current is higher than that in Schottky diode
(b) Schotty diode is much less than that of the PN-junction diode and the leakage current is higher than that in PN-junction diode
(c) Schottky diode is much less than that of PN - junction diode and the leakage current is less than that in PN-junction diode
(d) PN-junction diode is less than that of Schottky diode and the leakage current is less than that in Schottky diode.
Ans:-D
2. Match List-I with List-II and sc% the correct answer using the codes given below the lists:
List I
A. Semi converters
B. Source inductance of the converter
C. Sequence control of converters
D. Current limit control of converters
List II
1. Additional reactive power loading
2. Two quadrant operation with improved displacement factor on the ac side
3. Unity displacement factor
4. One quadrant operation with better displacement factor
Codes:
A B C D
(a) 2 1 4 3
(b) 2 3 4 1
(c) 4 1 2 3
(d) 4 3 2 1
Ans:-C
3. In the switched mode power supply (ac), the size of the transformer is reduced by operating
(a) both input and output side inverter with PWM (pulse width modulation) control at very low frequency
(b) both input and output side inverter with PWM control at very high frequency
(c) the output side inverter with PWM control at very high frequency
(d) the input side inverter with PWM control at very high frequency
Ans:-A
4. The insulation resistance of a 20 km long underground cable is 8 mega ohms. Other things being the same, the insulation resistance of a 10 km long cable will be
(a) 16 mega ohm
(b) 32 mega ohm
(c) 4 mega ohm
(d) 2 mega ohm
Ans:-A
5. A single-phase half bridge inverter has a resistive load of 2.4 ohms and a dc input voltage of 48 V with a centre tap. The rms output voltage of fundamental frequency is
(a) 21.6 V
(b) 43.2 V
(c) 20.6 V
(d) 40V
Ans:-A
6. The derivative of a step function is
(a) zero
(b) an impulse function
(c) a ramp function
(d) a constant
Ans:-B
7. The current in an inductor i L a first order circuit has an initial value of 3 amp and final value of 2 amp. If the natural frequency S = —3, then i L’ in amp, for t > 0 is given by
(a) 3 + 2e-3t
(b) 2 + 3e-3t
(c) 2 + e-3t
(d) 2 — e-3t
Ans:-C
8. Which of the following quantities are analogous in a Force-Current analogy?
1. Displacement and Inductance
2. Velocity and Voltage
3. Mass and Capacitance
Select the correct answer using the codes given below:
Codes:
(a) l, 2and3
(b) l and2
(c) 2and3
(d) l and3
Ans:-C
9. To detect the error between a reference shaft position and an output shaft position which of the following error detectors can be used?
1. A pair of tachogenerators
2. A pair of potentiometers
3. A synchro pair
Select the correct answer using the codes given below:
Codes:
(a) 1,2and3
(b) 1and2
(c) 2 and3
(d) l and3
Ans:-D
10. When 30 V dc is applied to the vertical deflecting plates of a cathode ray tube, the bright spot moves 1 cm away from the centre. If 30 V (rms) ac is applied, then the movement of the spot will be nearly
(a) 1cm
(b) 1.5 cm
(c) 2cm
(d) 3cm
Ans:-A
11. A spectrum analyser can be described as
(a) Voltage selective frequency meter
(b) Current selective frequency meter
(c) Frequency selective voltmeter
(d) a filter
Ans:-C
12. A thermocouple produces a voltage of 50 m V. Its internal resistance is 50?. The resistance of its leads is 10? The output is read by a PMMC meter having an internal resistance of 120 ? The output voltage indicated will be
(a) 50 mV
(b) 40 mV
(c) 33.3 mV
(d) 25.0 mV
Ans:-C
13. Match List-I (Type of instrument) with List-II (Suitability for measurement) and Select the correct answer using the codes given below the lists:
List—I
A. Moving iron
B. Electrodynamic
C. Induction
D. Electrostatic
List—II
1. Ac/dc voltage only
2. Ac/dc voltage / current only
3. Ac voltage/current/power only
4. Ac/dc voltage/current/power
5. Dc voltage/current
Codes:
A B C D
(a) 2 4 3 1
(b) 2 4 1 3
(c) 1 2 3 5
(d) 1 2 5 3
Ans:-B
14. A relay has a resistance of 300 ohm. It is switched on to a 110 V dc supply. If the current reaches 63.2 per cent of its final steady value in 0.002 second then the inductance of the circuit will be
(a) 0.001 H
(b) 0.002 H
(c) 0.06 H
(d) 0.6H
Ans:-D
15. Which one of the following is necessary for a triggering system for thyristors in a line commutator converter?
(a) It must use separate power supply
(b) It should provide a train of pulses
(c) It should be synchronised with the mains supply providing a single pulse of suitable value
(d) It should be synchronised with mains providing a train of pulses
Ans:-D
16. In sinusoidal PWM, there are m cycles of the triangular carrier wave, in the half cycle of reference sinusoidal signal. If the zero of the reference sinusoid coincides with the zero of the triangular carrier wave, then the number of pulses generated in each half cycles is
(a) m /m-1
(b) m+1/ m-1
(c) 1
(d) m -1 /m
Ans:-D
Instructions: The following items consist of two statements, one labelled the ‘Assertion A’ and the other labelled the ‘Reason R’. You are to examine these two statements carefully and decide If the Assertion A and the Reason R are individually true and if so, whether the Reason is a correct explanation of the Assertion. Select your answer to these items using the codes given below and mark your answer sheet accordingly.
17. Assertion (A): A BJT amplifier needs very good bias stabilization circuit as compared to that of an FET amplifier circuit.
Reason (R): The input p-n junction of FET amplifier is reverse biased and that of the BJT amplifier is forward biased.
Ans:-C
18. Assertion (A): A monostable multivibrator can be used as a counter.
Reason (R): The pulse width of the monostable. multivibrator is a function of its input dc voltage.
Ans:-A
19. Assertion (A): For a periodic input voltage whose amplitude is large enough to pass through the trip points, a Schmitt trigger produces a rectangular wave-form at the output.
Reason (R): A Schmitt trigger is a comparator with positive feedback and hence prevents noise triggering.
Ans:-B
20. Assertion (A): The multistage intermediate frequency amplifier of a super heterodyne radio receiver is always staggered tuned.
Reason (R): A very sharp tuned high gain amplifier is obtained maximizing the gain and increasing the fidelity of the receiver.
Ans:-B
21. A lamp rated at 10 watts, 50 volts is proposed to be used in 110 volts, system. The wattage and resistance of the resistor to be connected in series with the lamp should be
(a) l5watt, 350 ohms
(b) 10 watts, 250 ohms
(c) 12 watts, 300 ohms
(d) l5watts, 250 ohms
Ans:-C
22. Match List-I with List-Il and select the correct answer using the codes given below the lists:
List I
A. Superposition theorem
B. Thevenin theorem
C. Signal flow graph
D. Complex frequency
List II
1. Current source
2. Linearity
3. s-plane
4. Mason’s gain formula
5. Voltage source
Codes:
A B C D
(a) 2 1 4 5
(b) 1 2 4 5
(c) 2 5 3 4
(d) 2 5 4 3
Ans:-D
23. In a series resonant circuit, which one of the following will increase on increasing the inductance to four limes its value and reducing the capacitance to one-fourth of its value?
(a) Resonant frequency
(b) Current at resonant frequency
(c) Impedance at resonant frequency
(d) Selectivity of the circuit
Ans:-D
24. A series RLC circuit draws current at leading power factor at
(a) the resonant frequency
(b) frequencies less than the resonant frequency
(c) frequencies more’ than the resonant frequency
(d) frequencies both less and more than the resonant frequency
Ans:-B
25. One of the two wattmeters has read zero in the two-wattmeter method of power measurement This indicated that the load phase angle is
(a) 00
(b) 30°
(c) 60°
(d) 90°
Ans:-C
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