HPCL Electronics Question Paper

HPCL electronics and electrical solved question papers,

1. Removing bypass capacitor across the emitter-leg resistor in a CE amplifier causes

(A) increase in current gain.
(B) decrease in current gain.
(C) increase in voltage gain.
(D)decrease in voltage gain.
Ans: D

2. When a step-input is given to an op-amp integrator, the output will be

(A) a ramp.
(B) a sinusoidal wave.
(C) a rectangular wave.
(D) a triangular wave with dc bias.
Ans: A

3. Hysteresis is desirable in Schmitt-trigger, because

(A) energy is to be stored/discharged in parasitic capacitances.
(B) effects of temperature would be compensated.
(C) devices in the circuit should be allowed time for saturation and desaturation.
(D) it would prevent noise from causing false triggering.
Ans: C

4. Space charge region around a p-n junction

(A) does not contain mobile carriers
(B) contains both free electrons and holes
(C) contains one type of mobile carriers depending on the level of doping of the p or n regions
(D) contains electrons only as free carriers
Ans: A

5. When an amplifier is provided with current series feedback, its

(A) input impedance increases and output impedance decreases
(B) input and output impedances both decrease
(C) input impedance decreases and output impedance increases
(D) input and output impedances both increase
Ans: D

6. The fan-out of a MOS-logic gate is higher than that of TTL gates because of its

(A) low input impedance
(B) high output impedance
(C) low output impedance
(D) high input impedance

Ans: D

7. A highly stable resonance characteristic is the property of a ____ oscillator.

(A) Hartley
(B) Colpitts
(C) Crystal
(D) Weinbridge
Ans. (C)

8. A phase shift oscillator uses __________________.

(A) LC tuning
(B) Piezoelectric crystal
(C) Balanced bridge
(D) Variable frequency operation
Ans. (C)

9. A bistable multivibrator is a

(A) Free running oscillator.
(B) Triggered oscillator.
(C) Saw tooth wave generator.
(D) Crystal oscillator
Ans:B

10. The number of point to point links required in a fully connected network for 50 entities is

(A) 1250
(B) 1225
(C) 2500
(D) 50
Ans: (C)

11. The ________is a circuit-switched network, while the ______is a packet-switched network.

(A) Telephone, ATM
(B) SONET and FDDI
(C) Satellite, Telephone
(D) FDDI and SONET
Ans: (A)

12. Direct inward dialling is used as a feature in

(A) PSTN.
(B) PBX.
(C) EPABX.
(D) VPN.
Ans: (C)

13. ISDN handles data pertaining to

(A) All digital services
(B) Speech and Video
(C) Computer data only
(D) Speech only
Ans: (A)

14. A BJT operates as a switch

(A)under small signal conditions
(B)with no signal condition
(C)in the active region of transfer characteristic
(D)under large signal conditions
Ans:D

15. Bulk power transmission over long HVDC lines are preferred, on account of

(A)low cost of HVDC terminals
(B)no harmonic problems
(C)minimum line power losses
(D)simple protection

Ans:C

16. A converter which can operate in both 3-pulse and 6-pulse modes is

(A)1-phase full converter
(B)3-phase half wave converter
(C)3-phase semiconverter
(D)3-phase full converter
Ans:C

17. A three-phase semiconverter feeds the armature of a separately excited dcmotor, supplying a nonzero torque. For steady-state operation, the motor armature current is found to drop to zero at certain instances of time. At suchinstances, a voltage assumes a value that is

(A)equal to the instantaneous value of the ac phase voltage
(B)equal to the instantaneous value of the motor back emf
(C)arbitrary
(D)zero

Ans:B

18. The frequency of the ripple in the output voltage of a 3-phase semiconverter depends upon

(A)firing angle and load resistance
(B)firing angle and supply frequency
(C)firing angle and load inductance
(D)only on load circuit parameters
Ans:B

19. In dielectric heating, the rate of heating cannot be increased by increasing the potential gradient because

(A)Coupling problems become highly pronounced
(B)Very high voltages are not easily available
(C)Heating becomes non-uniform
(D)Corona takes place
Ans:D

20. The speed and torque of induction motors can be varied by which of thefollowing means?

(A)Stator voltage control
(B)Rotor voltage control
(C)Frequency control
(D)All of these

Ans:D