2019 SSC Junior Engineer Electrical Online Exam 2019 CPWD/CWC/MES Electrical Engineering Set 2.8

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71. Which of the following generators offers poorest voltage regulation ?




... Answer is B)
During On-load conditions its Diffentially Compounded DC generator that has the poorest voltage regulation.

In differential compound machine shunt and series field flux are subtracted and the net field flux is reduced. When the generator is loaded, load current (or armature current) flows through the series field windings creating magnetic flux that opposes the flux created by shunt field.
This results in decrease of induced emf and, therefore, in terminal voltage.
In such generators the terminal voltage drops very rapidly with the increase in load current and, therefore it is interesting to note that a short- circuit cannot cause any damage to it.

In such a generator, the induced voltage on no-load would be the same as for the shunt generator because series field does not create any flux.
So it behaves like DC shunt generator, which has a very good regulation.

For No- load conditions, DC series generator has the poorest regulation


72. transformer is usually mounted on a pole of plinth ?




... Answer is B)
Distribution transformer is usually mounted on a pole of plinth


73. While estimating the overhead lines, if the number of poles required are 14, then what is the estimated number of earth sets required ?




... Answer is C)
While estimating the overhead lines, the first and last pole is always earth connected and after every 3rd electrical pole, the fourth pole is earthed. Therefore, the approximate number of required ground set = 4

74. If the AC voltage and current are given by the following expressions?

v = 200sin (314t — 60°)
i = 50sin (720t), then what is the phase relation between them?




... Answer is A)
v = 200sin (314t — 60°)
i = 50sin (720t)
The frequency of the given voltage and current is not the same, hence their phase relationship cannot be known.
To find the phase relationship of any two zodiac signs, their frequency should be same.


75. A/An ........ is used in domestic mixers ?




... Answer is C)
Universal Motor
The motors which can be used with a single phase AC source as well as a DC source of supply and voltages are called as Universal Motor.
It is also known as Single Phase Series Motor.
A universal motor is a commutation type motor.
If the polarity of the line terminals of a DC Series Motor is reversed, the motor will continue to run in the same direction.


Applications of Universal Motor.
Portable drill machine. Used in hair dryers, grinders and table fans. A universal motor is also used in blowers, polishers and kitchen appliances.

76. If two impedances are given as Z1 = 20∠600 and Z2 = 5∠300, then Z1 / Z2 = ?




... Answer is C)
Z1 = 20∠60 °

Z2 = 5∠30 °>

Z1/Z2 = 20/5 (∠60° -∠30°)

Z1/Z2 = 4∠30°



77. The work done on or by a unit N-pole in moving once around a closed path is equal to ?




... Answer is C)
The work done on or by a unit N-pole in moving once around a closed path is equal to the product of current and number of turns enclosed by that path

MMF = NI
Magnetomotive force (mmf), Fm = NI ampere-turns (At), where N = number of conductors (or turns) and I = current in amperes.


78. The impedance at resonance offered by a parallel resonant circuit is ?




... Answer is B)
At resonance, currents IL and IC are equal and cancelling giving a net reactive current equal to zero.
... Since the current flowing through a parallel resonance circuit is the product of voltage divided by impedance, at resonance the impedance, Z is at its maximum value, ( =R ).



Also as the impedance of a parallel circuit changes with frequency, this makes the circuit impedance “dynamic” with the current at resonance being in-phase with the voltage since the impedance of the circuit acts as a resistance.
Then we have seen that the impedance of a parallel circuit at resonance is equivalent to the value of the resistance and this value must, therefore represent the maximum dynamic impedance (Zd) of the circuit as shown

Zd = L/CR

79. Observe the given table. The truth table represents gate ?




... Answer is D)
XOR gate is a digital logic gate that gives a true output when the number of true inputs is odd. An XOR gate implements an exclusive or; that is, a true output results if one, and only one, of the inputs to the gate is true.
If both inputs are false or both are true, a false output results..

80. The number of valence electrons of P and Si are .....respectively ?




... Answer is B)
Phosphorus (P) has 15 electron i.e 2,8,5. Hence the number of electron in its outermost orbit is 5.


Silicon (Si) has 14 electron i.e 2,8,4. Hence the number of electrons in its outermost orbit is 4.














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