Electrical Engineering test questions for exams and entrance - 6
(1) Let T be the time period of a periodic signal x (t) and for some time “t?” let y (t) = x (t - to) + x (t + to). Let b denotes the Fourier series coefficients of y (t). For all odd
values of k if b? = 0 then “to” can be equal to
(A) T/2
(B) 2T
(C) T
(D) T/4
View Answer / Hide Answer(2) The figure shows three subsystems connected in cascade. G1, G2 and 1/G3 are the respective gains of the system and ε1, ε2 and ε3 are the respective relative small
errors associated with each respective subsystem. The error associated with the output is
(A) ε1+ ε2 + ε3
(B) 1/ε1+ ε2 + ε3
(C) ε1+ ε2 - ε3
(D) ε1- ε2 + ε3
View Answer / Hide Answer(3) Consider a system 2/(s+1). For a step response to reach 98% of its final value, the approximate time taken will be
(A) 1s
(B) 4s
(C) 10s
(D) 8s
View Answer / Hide Answer(4) The logic gates that are designated as universal gates are
(A) AND, NAND and OR gates
(B) NOR and NAND gates
(C) AND, OR and NOT gates
(D) XNOR, NOR and NAND gates
View Answer / Hide AnswerANSWER: NOR and NAND gates
(5) Single slope integrating type and successive approximation type are the two 8-bit ADC’s and to convert 5v analog input signal into equivalent digital output they take time Ta and Tb
respectively. If the input analog signal is reduced to 2.5v then the approximate time taken by the two ADC’s will be respectively
(A) Ta/2, Tb
(B) Ta, Tb/2
(C) Ta, Tb
(D) Ta/2, Tb/2
View Answer / Hide Answer(6) For the signal h (t) the Fourier transform is H (jω) = (2cosω)(sin2ω)/ ω. The value of h (0) is
(A) 1/2
(B) 1/4
(C) 2
(D) 1
View Answer / Hide Answer(7) For the signal x (t) = 8 sin (0.8πt+π/4) the period is
(A) 0.8s
(B) 2.5s
(C) 1s
(D) 0.8πs
View Answer / Hide Answer(8) In a certain alternator a field excitation of 20 A results in an armature current of 400 A in short circuit and a terminal voltage of 2000V on open circuit. At a load current of 200A,
the magnitude of the internal voltage drop within the machine is
(A) 100V
(B) 10V
(C) 1000V
(D) 300V
View Answer / Hide Answer(9) The leakage flux in an induction motor is
(A) The flux that links the stator winding or the rotor winding but not both
(B) The flux that links both the stator winding and the rotor winding
(C) The flux that does not link any winding
(D) The flux that leaks through the machine.
View Answer / Hide AnswerANSWER: The flux that links the stator winding or the rotor winding but not both
For Questions 10 and 11 refer to the data given below:
While supplying the rated load at a speed of 80 rad/sed, a 240 V dc shunt motor draws 15 A current. Armature resistance = 0.5 Ω and field winding resistance = 80 Ω.
(10) At the time of plugging, the net voltage across the armature resistance will be
(A) 230V
(B) 324V
(C) 300V
(D) 474V
View Answer / Hide Answer(11) To limit the armature current to 125% of its rated value, the external resistance to be added in the armature circuit is
(A) 6.4 Ω
(B) 10.6 Ω
(C) 16.2 Ω
(D) 31.1 Ω
View Answer / Hide Answer(12) A 3-phase synchronous motor is connected to an ac main. The motor runs at full load and unity power factor. With field current held constant if its shaft load is reduced by half, its
new power factor will be
(A) Unity
(B) Lagging
(C) Leading
(D) Dependent on machine parameters.
View Answer / Hide Answer(13) Consider a unity feedback linear system. The steady state error of this system for a unit step input is 0.1. What will be the steady state error of the same system for a pulse input
whose magnitude is 10 and duration is of 1sec?
(A) 0
(B) 1
(C) 0.1
(D) 0.5
View Answer / Hide Answer(14) What is the common use of negative sequence relay?
(A) To protect a transformer
(B) To protect an alternator
(C) To protect a bus bar
(D) To protect a transmission line
View Answer / Hide AnswerANSWER: To protect an alternator
(15) When a triangular wave symmetric about the time-axis is fed to an average reading digital multimeter, it reads 10 V. The rms reading meter for the same input will read
(A) 10/√
3(B) 10√
2(C) 20/√
3(D) 20√
3View Answer / Hide Answer(16) There are two switches for a bulb, one switch at ground floor and the other one at the first floor. The bulb can be turned ON or OFF by any one of the switched irrespective of the
state of the other switch. This logic of switching of bulb resembles
(A) An OR gate
(B) A NAND gate
(C) An AND gate
(D) An XOR gate
View Answer / Hide Answer(17) What will be the content of accumulator after the instructions given below is executed in an 8085 microprocessor?
XRA A
MVI, B F0H
SUB B
(A) 10 H
(B) 01 H
(C) 0F H
(D) F0 H
View Answer / Hide Answer(18) A maximum frequency of 5Khz of a band-limited signal is to be sampled. The sampling frequency in KHz, which is not valid according to sampling theorem, is
(A) 20
(B) 15
(C) 5
(D) 10
View Answer / Hide Answer(19) A non-magnetic core has a mean circumference of 300mm and cross-sectional area of 300mm
². A coil of 300 turns is wound on it. What will be the inductance of the coil
corresponding to a magnetizing current of 3A?
(A) 132.01 μH
(B) 154.23 μH
(C) 101.32 μH
(D) 113.04 μH
View Answer / Hide Answer(20) The function f (t) = sin t / t at t=0 has
(A) A minima
(B) A maxima
(C) A discontinuity
(D) A point of inflection
View Answer / Hide Answer(21) The solution of the differential equation t dx/dt + x = t with initial condition x(1) = 0.5 is
(A) x = t
(B) x = t
²/2
(C) x = t/2
(D) x = 2t
View Answer / Hide Answer(22)
(A) 15A + 13I
(B) 15A + 15I
(C) 19A + 30I
(D) 19A + 19I
View Answer / Hide Answer(23) A salient pole alternator whose armature resistance is negligible has direct axis reactance of 1.2p.u and quadrature axis reactance of 1.0p.u. What is the power angle of this
alternator if it is delivering rated kVA at upf and at rated voltage?
(A) 45°
(B) 90°
(C) 120°
(D) 60°
View Answer / Hide Answer For Questions 24 and 25 refer to the diagram given below:
(24) The Thevenin’s equivalent resistance across the terminal A and B is
(A) 0.5Kohm
(B) 0.11Kohm
(C) 0.2Kohm
(D) 1Kohm
View Answer / Hide Answer(25) The Thevenin’s equivalent voltage across the terminal A and B is
(A) 1.5V
(B) 0.25V
(C) 0.5v
(D) 1V
View Answer / Hide Answer
