Questions And Answers

No. Question

1 The RMS value of the voltage u(t) =3 + 4cos (3t) is

Options

A)

Ö (17)

V B) 5 V

C) 7 V

Your Answer (Not Answered)

Correct Answer A

2

The open loop transfer function of a unity feed back control system is given as

G(s) =

as + 1

s2

The value of ‘a’ to give a phase margin of 45° is equal to

Options

A) 0.141 B) 0.441

C) 0.841 D) 1.141

Your Answer (Not Answered)

Correct Answer C

3 The armature resistance of a permanent magnet dc motor is 0.8 W. At no load, the motor draws 1.5 A from a supply voltage of 25 V and runs at 1500 rpm. The efficiency of the motor while it is operating on load at 1500 rpm drawing a current of 3.5 A from the same source will be

Options

A) 48.0% B) 57.1%

C) 59.2% D) 88.8%

Your Answer (Not Answered)

Correct Answer A

4 The solution of the first order differential equation x(t) = -3x(t), x (0) = x0 is

Options

A) x (t) = x0 e-3t B) x (t) = x0 e-3

C) x (t) = x0 e-1/3 D) x (t) = x0 e-1

Your Answer (Not Answered)

Correct Answer A

5 The unit impulse response of a second order under-damped system starting from rest is given by

c(t) = 12.5 e-6t sin 8 t, t 0

The steady-state value of the unit step response of the system is equal to

Options

A) 0 B) 0.25

C) 0.5 D) 1.0

Your Answer (Not Answered)

Correct Answer D

6

A single-phase, 230 V, 50 Hz, 4 pole, capacitor-start induction motor has the following stand-still impedances

Main winding Zm = 6.0 + j4.0 W

Auxiliary winding Za = 8.0 + j6.0 W

The value of the starting capacitor required to produce 90° phase difference between the currents in the main and auxiliary windings will be

Options

A) 176.84 mF B) 187.24 mF

C) 265.26 mF D) 280.86 mF

Your Answer (Not Answered)

Correct Answer A

7

A single-phase half-controlled rectifier is driving a separately excited dc motor. The dc motor has a back emf constant of 0.5 V/rpm. The armature current is 5 A without any ripple. The armature resistance is 2W. The converter is working from a 280 V, single phase ac source with a firing angle of 80°. Under this operating condition, the speed of the motor will be

Options

A) 339 rpm B) 359 rpm

C) 366 rpm D) 386 rpm

Your Answer (Not Answered)

Correct Answer C

8 The 8085 assembly language instruction that stores the content of H and L registers into the memory locations 2050H and 2051H, respectively, is

Options

A) SPHL 2050H B) SPHL2051H

C) SHLD 2050H D) STAX 2050H

Your Answer (Not Answered)

Correct Answer C

9 A 50 Hz, 4-pole, 500 MVA, 22 kV turbo-generator is delivering rated megavolt-amperes at 0.8 power factor. Suddenly a fault occurs reducing is electric power output by 40%. Neglect losses and assume constant power input to the shaft. The accelerating torque in the generator in MNm at the time of the fault will be

Options

A) 1.528 B) 1.018

C) 0.848 D) 0.509

Your Answer (Not Answered)

Correct Answer A

10 The Nyquist plot of loop transfer function G(s) H(s) of a closed loop control system passes through the point (-1, j0) in the G(s) H(s) plane. The phase margin of the system is

Options

A) 0° B) 45°

C) 90° D) 180°

Your Answer (Not Answered)

Correct Answer D

11

A 50 kW dc shunt motor is loaded to draw rated armature current at any given speed. When driven

(i) at half the rated speed by armature voltage control and

(ii) at 1.5 times the rated speed by field control, the respective output powers delivered by the motor are approximately.

Options

A) 25kW in (i) and 75kW in (ii) B) 25kW in (i) and 50kW in (ii)

C) 50kW in (i) and 75kW in (ii) D) 50kW in (i) and 50kW in (ii)

Your Answer (Not Answered)

Correct Answer B

12 A hydraulic turbine having rated speed of 250 rpm is connected to a synchronous generator. In order to produce power at 50 Hz, the number of poles required in the generator are

Options

A) 6 B) 12

C) 16 D) 24

Your Answer (Not Answered)

Correct Answer D

13 For the equation x(t)+3 x(t) +2x(t) = 5, the solution x (t) approaches which of the following values as t ® ¥ ?

Options

A) 0 B)

5

2

C) 5 D) 10

Your Answer (Not Answered)

Correct Answer B

14 The following motor definitely has a permanent magnet rotor

Options

A) DC commutator motor B) Brushless dc motor

C) Stepper motor D) Reluctance motor

Your Answer (Not Answered)

Correct Answer C

15 A110 kV, single core coaxial, XLPE insulated power cable delivering power at 50Hz, has a capacitance of 125 nF/km. If the dielectric loss tangent of XLPE is 2 x 10-4, the dielectric power loss in this cable in W/km is

Options

A) 5.0 B) 31.7

C) 37.8 D) 189.0

Your Answer (Not Answered)

Correct Answer D

16 The simultaneous application of signals x(t) and y(t) to the horizontal and vertical plates, respectively, of an oscilloscope, produces a vertical figure-of-8 display. If P and Q are constants, and x(t) = P sin (4t + 30), then y(t) is equal to

Options

A) Q sin (4t – 30) B) Q sin (2t + 15)

C) Q sin (8t + 60) D) Q sin (4t + 30)

Your Answer (Not Answered)

Correct Answer B

17 A 500 MW 3-phase Y-connected synchronous generator has a rated voltage of 21.5 kV at 0.85pf. The line current when operating at full load rated conditions will be

Options

A) 13.43 kA B) 15.79 kA

C) 23.25 kA D) 27.36 kA

Your Answer (Not Answered)

Correct Answer B

18

Total instantaneous power supplied by a 3-phase ac supply to a balanced R-L load is

Options

A) zero B) constant

C) pulsating with zero average D) pulsating with non-zero average

Your Answer (Not Answered)

Correct Answer B

19 The equivalent circuit of a transformer has leakage reactances X1 , X

Options

A) X1>> X B) X1<< X

C) X1» X D) X1» X

Your Answer (Not Answered)

Correct Answer D

20 If P and Q are two random events, then the following is TRUE

Options

A) Independence of P and Q implies that probability (P Q ) = 0

B) Probability (P Q ) Probability (P) + Probability (Q)

C) If P and Q are mutually exclusive, then they must be independent

D) Probability (P Q ) Probability (P)

Your Answer (Not Answered)

Correct Answer D