RailTel Latest Electrical and Electronics Question Paper with Answers
1. A motor which can conveniently be operated at lagging as well as leading power factors is the
(A) squirrel cage induction motor. (B) wound rotor induction motor. (C) synchronous motor. (D) DC shunt motor. Ans: C
2. An alternator is delivering rated current at rated voltage and 0.8 power-factor lagging case. If it is required to deliver rated current at rated voltage and 0.8 power-factor leading, the required excitation will be
(A) less. (B) more. (C) more or less. (D) the same. Ans: B EX:Over excitation gives leading power factor and under excitation gives lagging p.f .
3. A 1:5 step-up transformer has 120V across the primary and 600 ohms resistance across the secondary. Assuming 100% efficiency, the primary current equals
(A) 0.2 Amp. (B) 5 Amps. (C) 10 Amps. (D) 20 Amps. Ans: A EX: I1= V1 /R1 = 120/600 = 0.2 ( = 100%, losses are zero therefore V1 = VR = I1R1)
4. In case of a universal motor, torque pulsation is minimized by _________.
(A) load inertia (B) rotor inertia (C) both rotor and load inertia (D) none of the above
Ans: C Ex:In a universal motor, torque pulsation is minimized by rotor and load inertia.
5. The speed-torque characteristics of a DC series motor are approximately similar to those of the _________motor.
(A) universal (B) synchronous (C) DC shunt (D) two-phase Ans:A
6. In the heating process of the ________type a simple method of temperature control is possible by means of a special alloy which loses its magnetic properties at a particular high temperature and regains them when cooled to a temperature below this value.
(A) Indirect induction over (B) core type induction furnace
(C) coreless induction furnace (D) high frequency eddy current Ans: D
7. The voltage at the two ends of a transmission line are 132 KV and its reactance is 40 ohm. The Capacity of the line is
(A) 435.6 MW (B) 217.8 MW (C) 251.5 MW (D) 500 MW Ans: A EX:Line capacity is determined by power of line
P = (V2/R) or (V2/Z) when cos =1
8. Skewing in the slots of an induction motor is provided to reduce
(A) iron loss (B) noise (C) harmonics (D) temperature rise. Ans:C
9. The losses occurring in the rotor of an induction motor are less than those in the stator because of
(A) small diameter of rotor (B) less rotor frequency (C) slot skewing (D) none of the above Ans:B
10. Which test is conducted on transformers to check its ability to withstand the transient voltages due to lightening etc. ?
(A) Induced over voltage test (B) Partial discharge test (C) Impulse test (D) Any of the above. Ans:C
11. The output of a rotating electrical machine is limited by
(A) size of the machine (B) peripheral velocity (C) temperature rise (D) none of the above.
12. A synchronous machine having large length of the air gap will have
(A) higher noise level
(B) smaller unbalanced magnetic pull (C) lower limit of stability (D) higher value of inherent regulation. Ans:B
13. For the load cycle shown in the figure, the rating of the motor should be
(A) 600 kW (B) 350 kW (C) 300 kW (D) 275 kW. Ans:D
14. The primary winding of a 220/6 V, 50 Hz transformer is energised from 110 V, 60 Hz supply. The secondary output voltage will be
(A) 3.6 V. (B) 2.5 V. (C) 3.0 V. (D) 6.0 V. Ans: C
15. The maximum power for a given excitation in a synchronous motor is developed when the power angle is equal to
(A) 0o (B) 45o (C) 60o (D) 90o
P = VI cos
Pmax = VI
16. 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
17. In an intrinsic semiconductor, the Fermi-level is
(A) closer to the valence band (B) midway between conduction and valence band (C) closer to the conduction band (D) within the valence band Ans: C
18. A highly stable resonance characteristic is the property of a ____ oscillator.
(A) Hartley (B) Colpitts (C) Crystal (D) Weinbridge Ans. (C)
19. For a JFET, when VDS is increased beyond the pinch off voltage, the drain current
(A) Increases (B) decreases (C) remains constant. (D) First decreases and then increases.
20. A radio frequency signal contains three frequency components, 870 KHz, 875 KHz and 880 KHz. The signal needs to be amplified. The amplifier used should be
(A) audio frequency amplifier (B) wide band amplifier (C) tuned voltage amplifier (D) push-pull amplifier Ans. (C) EX:We need to amplify 3 signal frequencies i.e., 870 kHz, 875 kHz and 880 kHz. These frequencies lie in a bandwidth of 10 kHz and we should use only tuned voltage amplifiers to amplify them.
21. An oscillator of the LC type that has a split capacitor in the circuit is
(A) Hartley oscillator (B) Colpitts oscillator (C) Weinbridge oscillator (D) R-C phase shift oscillator Ans. (B)
22. In the voltage range, Vp < VDS < BVDSS of an ideal JFET or MOSFET
(A) The drain current varies linearly with VDS. (B) The drain current is constant. (C) The drain current varies nonlinearly with VDS. (D) The drain current is cut off. Ans: (B)
23. In a clamping circuit, the peak-to peak voltage of the waveform being clamped is
(A) affected by the clamping (B) not affected by the clamping (C) determined by the clamping voltage value (D) determined by the ratio of rms voltage of the waveform and the clamping voltage Ans: B
24. A ‘literal’ in Boolean Algebra means
(A) a variable inn its uncomplemented form only (B) a variable ORed with its complement (C) a variable in its complemented form only (D) a variable in its complemented or uncomplemented form Ans: D
25. The maximum possible collector circuit efficiency of an ideal class A power amplifier is
(A) 15% (B) 25% (C) 50% (D) 75% Ans:C
26. Which of the following parameters is used for distinguishing between a small signal and a large-signal amplifier?
(A) Voltage gain (B) Frequency response (C) Harmonic Distortion (D) Input/output impedances Ans: D
27. A single phase diode bridge rectifier supplies a highly inductive load. The load current can be
assumed to be ripple free. The ac supply side current waveform will be
(A) sinusoidal (B) constant dc. (C) square (D) triangular
28. The breakdown mechanism in a lightly doped p-n junction under reverse biased condition is called
(A) avalanche breakdown. (B) zener breakdown. (C) breakdown by tunnelling. (D) high voltage breakdown.
29. For a large values of |VDS|, a FET – behaves as
(A) Voltage controlled resistor. (B) Current controlled current source. (C) Voltage controlled current source. (D) Current controlled resistor.
30. The minimum number of flip-flops required to construct a mod-75 counter is
(A) 5 (B) 6 (C) 7 (D) 8