General EE Flashcards
The tendency of electron dipole moments to align with an applied magnetic field
Paramagnetism
If a circuit has L closed loops, B branches, and J junctions the number of independent loop equations is:
B – J + 1
It is the magnetic dipole moment per unit volume of an object
Magnetization
For any circuit the number of independent equations containing emf’s, resistances and currents equals:
the number of branches
“The sum of the currents into a junction equals to sum of the currents out of the junction” is a consequence of:
Conservation of charge
Faraday’s law states that an induced emf is proportional to:
the rate of change of the magnetic flux
It is the tendency of electron dipole moments to align with each other
Ferromagnetism
For an ohmic substance, the electron drift velocity is proportional to:
the electric field in the sample
The resistance of resistor 1 is twice the resistance of resistor 2. The two are connected in series and a potential difference is maintained across the combination. Then the potential difference across 1 is_______ that across 2
twice
If both the plate area and the plate separation of a parallel-plate capacitor are doubled, the capacitance is:
unchanged
A battery is connected across a series combination of two identical resistors. If the potential difference across the terminals is V and the current in the battery is i, then the potential difference across each resistor is ____ and the current in each resistor is ___.
V/2, I
“The sum of the emf’s and potential differences around a closed loop equals zero” is a consequence of:
Conservation of energy
An electron is accelerated from rest through a potential difference V. Its final speed is proportional to:
Sqrt V
For loop of a current-carrying wire in a uniform magnetic field the potential energy is a minimum if the magnetic dipole moment of the loop is:
in the same direction as the field
In a three-phase synchronous converter, the ratio of the AC voltage to DC Voltage is.
0.612
True or False
A magnetic field CANNOT change the kinetic energy of a charged particle
True
For three-phase induction motors which of the following is the least efficient method of speed control?
Rheostatic control
A complex voltage wave is applied across a pure capacitor. As compared to the fundamental voltage, the reactance offered by the capacitor to the third harmonic voltage would be
One-third
Which of the following harmonic voltage components in a 3-phase system would be in phase with each other?
2nd, 4th, 6th, etc
The skin effect of a conductor will reduce as the Resistivity of conductor material ________
increases
To make a galvanometer into an ammeter, connect:
a low resistance in parallel
By which of the following methods the protection against direct lightning strokes and high voltage sweep waves is provided?
Lightning arresters and ground wires
A periodic waveform possessing half-wave symmetry has no
Even harmonics
Poles which carry transformers are usually
H-type
In a Fourier series expansion of a periodic function, the coefficient a₀ represents its
DC value
The dc motor terminal voltage supplied by a solid-state chopper for speed control purposes varies ____ with the duty ratio of the chopper
linearly
The impedance of an RLC series circuit is definitely increased if:
R increases
If the field circuit of a loaded shunt motor is suddenly opened
circuit breaker or fuse will open the circuit before too much damage is done to the motor
In a dc generator, the effect of armature reaction on the main pole flux is to:
Both reduce it and distort it
The primary reason why open-circuit test is performed on the low-voltage winding of the transformer is that it
draws sufficiently large on-load current for convenient reading
Displacement current exists wherever there is:
a changing electric field
The purpose of Milliken’s oil drop experiment was to determine:
the charge of an electron
A uniformly loaded dc distributor is fed at both ends with equal voltages. As compared to a similar distributor fed at one end only, the drop at middle point is ________.
one-fourth
Which class of induction motor will be well suited for large refrigerators?
Class C
What is the main reason that alternating current replaced direct current for general use?
AC voltage may be conveniently transformed.
According to Gauss’ law for magnetism, magnetic field lines:
form closed loops
A magnetic field exist between the plates of a capacitor while:
the capacitor is being charged
Transformer cores are laminated in order to:
minimize eddy current loss
If residual magnetism of a shunt generator is destroyed accidentally, it may be restored by connecting its shunt field
to a dc source
A positively charged ion, due to a cosmic ray, is headed through Earth’s atmosphere toward the center of Earth. Due to Earth’s magnetic field, the ion will be deflected:
east
Gauss’ law for magnetism tells us that magnetic monopoles ____________
do not exist
A solid-state chopper converts a fixed-voltage dc supply into a
variable-voltage dc supply
In a sinusoidally driven series RLC circuit the current lags the applied emf. The rate at which energy is dissipated in the resistor can be increased by:
decreasing the capacitance and making no other changes
Turn-off time of an SCR is measured from the instant
anode current becomes zero
The capacitor used in auto transformer circuit for sodium vapor lamps, is for
for improving the power factor of the circuit
The magnetic properties of material stem chiefly from:
electron magnetic dipole moments
If a shunt motor running with a load has its shunt field opened, how would this affect the speed of the motor?
It will speed up.
The di/dt capability of a thyristor increases when the gate current:
increases
On an analog wattmeter, what part of the scale is most accurate and how much does that accuracy extend to the rest of the reading scale?
The accuracy is only at full scale, and that absolute number reading is carried through to the rest of the range. The upper 1/3 of the meter is the only truly calibrated part.
A cylindrical region contains a uniform electric field that is parallel to the axis and is changing with time. If r is the distance from the cylinder axis the magnitude of the magnetic field outside the region is:
proportional to 1/r
In a mercury vapor lamp light red objects appear black due to
absence of red light from lamp radiation
A sinusoidal emf is connected to a parallel plate capacitor. The magnetic field between the plates has _______ waveform and its amplitude _______ is to the frequency of the source
sinusoidal, proportional
In an RLC series circuit, the source voltage is leading the current at a given frequency f. If f is lowered slightly, then the circuit impedance will:
decrease
The polarity of an unmarked magnet can be determined using:
a compass
In a commutation circuit, employed to turn-off an SCR, satisfactory turn-of is obtained when
Circuit turn-off time > device turn-off time
Two wires made of the same material have the same lengths but different diameters. They are connected in parallel to a battery. The quantity that is NOT the same for the wires is:
the current
When a lead-acid storage battery is being charged, a harmful effect to humans is:
Emission of hydrogen gas.
For current to flow in an NPN silicon transistor’s emitter-collector junction, the base must be:
At least 0.7 volts positive with respect to the emitter.
What occurs if the load is removed from an operating series DC motor?
It will accelerate until it falls apart.
The primary of an ideal transformer has 100 turns and the secondary has 600 turns. Then the primary current is ____ times the secondary current
six
For a Y – Δ transformer Y – side grounded, the zero sequence current exists in the
lines on they – side
In a DC motor, what is the definition of “field resistance”?
It is the resistance of the excitation circuit.
Helmholtz coils are commonly used in the laboratory because the magnetic field between them:
is nearly uniform
The disadvantages of transmission line as compared to cable system are
atmospheric hazards like smoke, ice fumes, exposures to lighting, interference of telecommunication circuits etc.
The material used for fuse wire must have
low melting point and high specific resistance
The positive sequence component of voltage at the point of fault is zero when it is a
three-phase fault
A dielectric slab is slowly inserted between the plates of a parallel plate capacitor, while the potential difference between the plates is held constant by a battery. As it is being inserted the capacitance and the charge on the positive plate _________ but the potential difference between the plates ______________
increase, remains the same
If the torque angle is continuously increasing, the system will become __________.
unstable
The effective resistance of conductor is increased by ________.
Both skin effect and proximity effect
Wideband FM is preferable to narrowband FM for music transmission because:
The fidelity is better
What characteristic of plates of the battery is where Ampere-hour is rated?
area
Receptacle outlet shall be located on or above, but not more than ______ above countertop or work surface.
500 mm
What is the maximum number of conductors in a raceway that does not need to be derated?
3
This is the maximum continuous anode direct current that the device can withstand in the conduction state under specified conditions.
average forward current
Ideal transformer assumptions do not include zero reactance of the winding. True or False?
True
“In any linear bilateral network, if a source of emf E is any branch produces a current I in any other branch, the same emf acting in second branch would produce the same current I in the first branch”. This statement is associated with ___.
Reciprocity Theorem
For small values of drain-to-source voltage, JFET behaves like a
resistor
In EPIRA, what does OARC stand for?
Open Access and Retail Competition
Name the effect which is resulted because of the size of conductor, frequency, and the specific resistance of conducting material.
proximity effect
In turning off an SCR, a particular method is used wherein this basically requires momentarily forcing current through the SCR in the direction opposite to the forward conduction so that the net forward current is reduced below the holding value. What is this method?
forced commutation
Motors must be labeled with the following nameplate rating, manufacturer’s name and etc. This is known as the _________.
manufacturing rule
What is the heating process that makes use of the currents induced by the electromagnetic action in the charge to be heated. It is used for hardening of steel?
Induction heating
What is the maximum allowable continuous load for branch circuit conductor?
0.8
The skin effect in conductors is due to non-distribution of current in it and major portion of the current is near the ________ of conductor.
surface
This is the least prevalent shunt fault among transmission and distribution lines.
LLL
A resistance having a rating of 10 ohms, 10W is like to be a ___.
Wire Wound Resistor
For proper parallel operation, ac polyphaser alternators must have the same______.
voltage rating
In a BJT, largest current flow occurs in the _____
emitter
When a power plant is not able to meet the demand of consumers it will resort to _______.
load shedding
In a capacitor the electric charge is stored in:
dielectric
A capacitance C is charged through R. The time constant of the charging circuit is given by:
RC
In steam power plant which component needs maximum maintenance attention?
Boiler
The current flowing in L and C at parallel resonant are:
equal
Overvoltage relay device function number is ______________.
59
An AM transmitter using a class-C PA should employ:
High-level modulation
The minimum size of conductors to be used for lighting purposes is _____.
2.0 mm²
At a DC steady state, capacitor looks like a/an _______ circuit and an inductor looks like a/an ______ circuit.
opened, shorted
A substance or material having relative permeability of less than unity is classified as:
Diamagnetic
The useful life of diesel engine in a power plant is expected to be ______ year/s.
15
In a junction transistor, the collector cut-off current ICBO reduces considerable by doping the collector with ________
low level of impurity
Is the Collecting Efficiency included in the evaluation of the Technical Performance of a Distribution System according to Philippine Distribution Code (PDC)?
No
In positive voltage sequence, the line voltage leads the phase voltage by 30°. True or False
True
The direction of induced EMF can be found by using the principle of ______.
Fleming`s Right Hand Rule
In the solution of load flow equation, Newton-Raphson (NR) method is superior to the Gauss-Seidel (GS) method, because the _______ of the NR methods are not affected by ___________
convergence characteristic , selection of slack bus.
In a Zener diode shunt voltage regulator, the diode regulates so long as it is kept in _______ condition.
reverse
AC system has the following disadvantages over DC system EXCEPT:
charging current exists
An emf induced by the changing of current in the neighboring coil is called:
Mutually Induced
An inductance L and resistance R are connected in series to an ideal battery. A switch in the circuit is closed at time 0, at which time the current is zero. The energy stored in the inductor is a maximum:
a long time after the switch is closed
In the analysis of short transmission lines which of the following is neglected?
Shunt admittance
Maxwell’s L/C bridge is so called because:
For balance, it uses two opposite impedances in opposite arms
The meter that is suitable for only direct current measurements is:
Permanent-magnet type
The voltage regulation in magnetic amplifier type voltage regulator is affected by:
varying the reactance
The bundling of conductors is done primarily to:
reduce reactance
The Fourier series of a waveform possessing odd quarter-wave symmetry contains only
Odd sine terms
increased effective resistance but reduced effective internal reactance of. the conductor results to
Skin effect
During storm the live conductor of public electric supply breaks down and touches the earth. The consequences will be:
current will flow to earth
DMC was created by the Energy Regulatory Commission to monitor the compliance of the distribution utilities to the PDC. DMC stands for ________.
Distribution Management Committee
In practice, the three phase conductors of a three-phase line are seldom equilaterally spaced. The usual nonsymmetrical spacing produces unequal inductances in the three phases, leading to unequal voltage drops and imbalance in the line. To offset this imbalance, the positions of the conductors are interchanged at regular intervals in the line. This practice is known as ______.
Transposition
For two alternators operating in parallel, if the load shared by one of the alternators is to be increased, the field excitation is ______ but input torque should be ________
be kept constant, increased
What characteristic of plates of the battery is where Ampere-hour is rated?
Area
The current flowing in L and C at parallel resonant are:
equal
Positive charge is distributed uniformly throughout a non-conducting sphere. The highest electric potential occurs ______.
at the center
A ________ substance is one through which the magnetic lines of force can pass very easily
permeable
In a SCR circuit, the angle of conduction can be changed by changing:
Gate current
In a capacitor the electric charge is stored in:
dielectric
It is the steady current that produces the same rate of heating in a resistor as the actual current.
rms value of an AC current
_________ are used to control both magnitude and phase of the ac line current from the utility.
Static VAR compensators
What is the primary function of the tubes welded on the side of oil-type transformer?
To improve the cooling.
In a communication system, noise is most likely to affect the signal in the ________
channel
True or False: Windows 98 is RTOS (Real Time Operating System)
False
A car battery is rated at 80 ampere-hour. An ampere-hour is a unit of _____.
charge
What does IEMOP stand for?
Independent Electricity Market Operator of the Philippines
The purpose of a grid system is to:
interconnect the power stations
It is recommended to use UJT oscillator for gate-triggering of the thyristors mainly because:
It provides sharp firing pulses.
Power factor of synchronous motor can be made leading by adjusting its:
Excitation
What does PEMC in EPIRA stand for?
Philippine Electricity Market Corporation
One primary and one secondary terminal of a two-winding transformer is connected to an ohm-meter instrument. What will be the reading on this instrument?
Infinity
True or False:
Faraday’s Law states that an induced electromotive force is proportional to the rate of change of magnetic flux.
True
Which of the following statement is CORRECT concerning electric field?
A charged point particle released from the rest moves along a field line.
The breakdown mechanism in a lightly doped p-n junction under reverse biased condition is called:
Avalanche breakdown
Does the Differential relay protective relay/s operates on the principle of the Kirchhoff’s Current Law?
Yes
In a low-level AM system, amplifiers following the modulated stage must be:
Linear devices
In a DC transmission line, are there effects due to inductive and capacitive reactances?
None
For a JFET, when V_DS is increased beyond the pinch off voltage, the drain current:
Remains constant.
Removing bypass capacitor across the emitter-leg resistor in a CE amplifier causes ______ in voltage gain
Decrease
The boundary of the protection system is determined by the location of ____________.
current transformers
Which of the following is the electrical device that is usually required to be installed in moisture area in the dwelling unit in order to protect the person from electric shock?
Ground-Fault Circuit Interrupter
String efficiency is used for measuring the:
Degree of utilization SCRs.
Guy wire is used in the construction of distribution lines for what purpose?
Supporting the pole
Which of the following refers to the power loss due to alternating magnetization and demagnetization of the core material?
Hysteresis loss
The direction of induced EMF can be found by ______.
Fleming`s Right Hand Rule
GMC was created by the Energy Regulatory Commission to monitor the compliance of the users of the Grid to the PGC. What does GMC stand for?
Grid Management Committee
The value of the resistor creating thermal noise is doubled. The noise power generated is therefore:
Unchanged
Name the effect which is resulted because of the size of conductor, frequency, and the specific resistance of conducting material.
proximity effect
When transistors are used in series or parallel, a snubber circuit is used to:
Limit di/dt
When the amplitude of the oscillator in a series RLC circuit is doubled, the Current amplitude is ___________.
doubled
The skin effect in conductors is due to non-distribution of current in it and major portion of the current is near the ________ of conductor.
surface
A capacitance C is charged through R. The time constant of the charging circuit is given by:
RC
The effective resistance of conductor is increased by ________.
Both skin effect and proximity effect
True or False
A pre-emphasis circuit provides extra noise immunity by amplifying the high audio frequencies
True
If both the resistance and the inductance in an LR series circuit are doubled the new inductive time constant will be:
unchanged
True or False:
Capacitor motors have lower starting torque than comparably sized single-phase induction motor.
False
The ________ is used to protect the Oil immersed transformers against all internal faults
Buchholz relay
According to Gauss’ law for magnetism, magnetic field lines forms:
closed loops
Three phase transformers which cannot be connected in parallel are
Y – Y with Y – Δ
True or False: Magnetic flux lines do not have sources or sinks.
True
True or False:
A compound motor’s speed remains fairly constant when subjected to sudden loads
False
Lightning arresters are located _______
Near the transformer
Corona loss can be reduced by the use of hollow conductor because:
for a given cross-section, the radius of the conductor is increased
For the stable operation of interconnected system, the passive element that can be used as interconnecting element is:
reactor
In which of the following given faults, all the sequence currents are equal?
LG
If the transmission voltage increased, the percentage resistance drop will:
Decrease
The magnetic saturation curve limits the voltage at which a generator or motor can operate. Does saturation depend upon the type of steel used in the poles.
No
A battery is used to charge a parallel-plate capacitor, after which it is disconnected. Then the plates are pulled apart to twice their original separation. This process will double the:
stored energy
A DC system can be protected from lightning by including a thyrite tube in the circuit that connects the high-voltage line with the ground. Does its fusable link melt at high voltages?
No
Two parallel-plate capacitors with the same plate separation but different capacitances are connected in parallel to a battery. Both capacitors are filled with air. The quantity that is NOT the same for both capacitors when they are fully charged is:
charge on the positive plate
Do magnetic field lines cross themselves only at right angles?
No.
In a DC motor, what is the definition of “field resistance”?
It is the resistance of the excitation circuit.
Which of the following effects are generally less for an alternating current than for a direct current?
Chemical effects
The material used for fuse wire must have:
low melting point and high specific resistance
The class C insulation can withstand:
180°C
The percent bias for a generator protection lies between ____ to ____.
5 to 10
An essential requirement of peak load plant is that It should be capable of ________
starting quickly.
Induction regulators are used for voltage control in what part of the power system?
primary distribution
True or False
The current is produced by both holes and electrons when a P-N junction is forward-biased:
True
Floating neutral, in 3-phase supply, is undesirable because it causes:
unequal line voltages across the load
Which should be used for extinguishing electrical fires?
Carbon tetrachloride fire extinguisher
The ripple factor of a power supply is a measure of:
its filter efficiency
Power loss due to corona is not directly proportional to spacing between conductors. True or False
True
As compared to a LED display, the distinct advantage of an LCD display is that it requires ________ power
extremely low
The leakage current of a P-N diode is caused by:
heat energy
The magnetic saturation curve limits the voltage at which a generator or motor can operate. Does saturation depend upon the type of steel used in the poles?
No
For a lumped inductive load, with increase in supply frequency, P _______ and Q ________
decreases, increases
FDLF method is suitable for
high voltage transmission system
Which material is used for the manufacture of bus bars?
Copper rods
Why solid type of conductors is not preferred for the voltages exceeding 66 kV?
A danger of breakdown of insulation.
If any two phases for an induction motor are interchanged:
The motor will run in the reverse direction.
Are contact devices used for the measurement of level more reliable than devices which do not make contact with the material?
No
The term ‘cogging’ is associated with:
Induction motor
The good power factor of an induction motor can be achieved if the average flux density in the air gap is ____.
small
The thickness of insulation provided on the conductor in the cable depends on which among the following factors?
Operating voltage
The stator core is usually fabricated out of _______
Silicon steel
What kind of reactor is used to bring down the fault level within the capacity of the switchgear instrument?
Series reactor
In the manufacture of transformers, ANSI prescribes certain standards. One of it is that high voltage side should lead the low voltage side by 30° with Y - Δ or Y - Δ connections. True or False
True
Why is the single core cable not provided with armoring?
Avoids excessive loss in the armor.
In this gauge, the Low pressure fluid is compressed to a high pressure which is read by the monometer technique.
McLeod gauge
What is the value of the zero-sequence current compared to the current in the neutral wire?
1/3 times
Bedding’s purpose is both to protect the sheath against corrosion and to protect the sheath from mechanical injury due to armoring. True or False
True
In fiber-optic level sensors, the amount of light loss depends on:
The proportion of cable that is submerged in the liquid.
For induction motor at standstill condition, what is the value of slip?
1
In three-phase squirrel-cage induction motors, rotor conductors are short-circuited through end rings. True or False?
True
Can the rotameter be used for the application in automatic control scheme?
Yes
If real power demand is suddenly increased, frequency of the system will ______.
decrease
A squirrel-cage motor has such low resistance that it draws excessive current when starting. Will using a class A motor reduce this problem?
No
The rapid exponential decay in just a few cycles of the charge on the plates of capacitor in an RLC circuit might be due to:
a large resistance
Voltage magnitude of a particular bus can be controlled by controlling the:
reactive power of the bus
In terms of efficiency, shunt and series motors or generators have similar characteristics. Does the two type of motor have very similar efficiency curves?
No
Series and shunt motors are connected like series and shunt generators, respectively. The terms refer to the manner in which the self-excitation of the poles is connected to the unit.
Is it true that the torque curves of both shunt and series motors are not affected by the value of the armature current.
False
A long transmission line has certain values of parameters A, B, C, D. If the length is made 100 km thus the parameter A ________ and B _______
A increases B decreases
What will be the electrostatic force between the bodies, if the magnitude of the charge on two identical charged bodies is doubled?
Quadrupled
Two charges Q₁ and Q₂ are separated by a distance D. what is the effect on the force if Q₁, Q₂ and D are all doubled?
Remains the same
Friction and windage losses in induction motor is _______ of rated output.
1%
It is the decrease in dielectric strength of any mixtures of gases.
Penning effect
In lap winding, equalizer rings are used to save:
Brushes from carrying circulating currents.
Current chopping mainly occurs in which circuit breaker?
Air plant circuit breaker
The frequency of the humming tone in a transformer is _____
100 Hz.
For Paschen’s law to be valid which is the essential condition?
Temperature must be constant
Which part of the transformer is most prone to damage due to overheating?
Winding insulation
Fuse wire protection system is not used beyond:
100 A
Consider two capacitors. The second of two capacitors has twice the charge and half the voltage. What is the capacitance of the second capacitor?
Four times that of the first
When all the 3 phases are short circuited, it gives rise to:
Symmetrical fault current
For a simple lap winding, the commutator pitch is equal to:
± 1
The percentage of silicon in transformer stamping is usually limited to ____.
4%
The shaft of electric motor is generally supported in:
Ball or roller bearing
At what power angle the transmission line should be operated for stability and economy?
30° to 45°
The main consideration for higher operating voltage of transmission is to:
increase power transfer capability
The effects of electric shock in the human body will depend on:
current flowing in the body
What do you call the peripheral distance between the center of two adjacent poles in a DC machine
Pole pitch
Regarding rotating machinery, at zero power factor, the generator delivers real power to a load. True or False?
False
The area of hysteresis loop is a measure of:
Energy loss per cycle
Coulombs law for the force between electric charges most closely resembles with:
Newton`s law of gravitation
When two electricity neutral materials are rubbed together, one acquires a net positive charge and the other:
Gains electrons
________ is the amount of energy which must be given to an electron to move it to valence band
Fermi energy
What is the resistivity of semiconductor at room temperature?
0.01 to 50 ohm–cm
Is Electric Field Intensity a vector quantity?
Yes
What do you use to measure the dissipating factor of a capacitor?
Schering Bridge
Two charges Q1 and Q2 are separated by a distance D. what is the effect on the force if Q1, Q2 and D are all doubled?
Remains the same
The number of atoms or ions surrounding and touching a central atom is called
Ligancy
What will be the electrostatic force between the bodies, if the magnitude of the charge on two identical charged bodies is doubled?
Quadrupled
Which law is the magnetic equivalent of coulomb’s law?
Biot savart law
Temperature beyond which substances lose their ferroelectric properties is known as:
Curie temperature
The line imperfection in a crystal known as ______.
Edge dislocation
What is the value of dielectric constant for most of the solid substance?
Between 1 and 10
According to Steinmetz Hysteresis Law, hysteresis loss in a material is proportional to the flux density raised to:
1.6
Can Teflon be used at temperatures above 100 degrees C?
Yes
What is the percentage of carbon in mild steel?
0.08 to 0.3%
Is Pelton wheel a reaction turbine?
No
Measurement of ________ is affected by the presence of thermo-emf in the measuring circuit
high resistance
High voltage transmission efficiency is in the range of
85-95%
A BJT is said to be operating in the saturation region if
both the junctions are forward biased
In suspension type insulator the potential drop is maximum across the _____
lowest disc
In which industry are all the motors totally enclosed and moisture proof?
Paper industry
In a 3-phase synchronous generator, the stator winding is connected in star, because a delta connection would
have circulating currents due to triple harmonics
EMF induced in a coil rotating in a uniform magnetic field will be maximum when the rate of change of flux linkage is:
maximum
The response time of an indicating instrument is determined by its
damping system
What bridge is generally used for measurement of frequency and also capacitance?
Wein bridge
If the frequency of a transmission system is changed from 50 Hz to 100 Hz, the string efficiency
will decrease
The number of commutator segments in a dc machine is equal to the number of:
Coils
A DC voltage source is connected across a series RLC circuit. Under steady state conditions the applied DC voltage drops entirely across the:
C only
The number of parallel paths in an integral slot winding with P poles is:
P/2
The voltage of the bus-bar to which several alternators that are paralleled may be raised by simultaneously increasing field excitation of all alternators. True or False
True
Oil for transformer cooling should have ____ viscosity
Low
Why is skewing done in rotor slots?
To suppress unwanted harmonics.
What type of winding is the armature of a dc machine?
A closed-circuit winding.
When two electricity neutral materials are rubbed together, one acquires a net positive charge and the other
Gains electrons
When will the amount of back emf of a shunt motor increase?
When the field is strengthened.
Resistance switching is normally employed in what circuit breakers?
air blast circuit breakers
Which material for heating element should be selected if a furnace is to be used for heating up to temperature around 1500°C?
Platinum-molybdenum carbon compound
Low frequency operation of AC series motor in traction application Improves its:
commutation, pf and efficiency
The damping in D’ Arsonval galvanometer is obtained by ______.
eddy current induced in metal discs
The purpose of choke in a fluorescent tube is to _____.
increase voltage momentarily
Consider a constant uniform magnetic field. A conductor moves across this field at a constant velocity. The emf induced in the conductor is termed as ____.
dynamically induced emf
What is the pitch factor for a full pitched winding of a synchronous machine?
1.0
In which single-phase motor, the rotor has no teeth or winding?
Hysteresis motor
In the measurement of power in a balanced 3 phase circuit by two-wattmeter method if the two wattmeter’s show equal readings, then what is the power factor of the circuit?
unity
Alternator used in hydropower station has more number of poles in it than used in thermal power station, because
speed of its prime mover is less
The household energy meter is what kind of instrument?
integrating instrument
A commutator in a dc machine provides __________ rectification.
Full wave
What is the range of thickness of lamination of the core of a power transformer?
0.03 to 0.5 mm
When back emf of a dc motor vanishes suddenly, then:
The motor burns.
In class – B dc motor, what is the maximum permissible temperature rise in the armature winding?
75 degrees C
For induction motor, the ratio of length to pole pitch for good efficiency is taken as:
1.5 to 2
Can Mica be used for temperatures up to 500 degC?
Yes
The unvarying load on a power station which occurs almost the whole day on the station is known as:
Base load
Does the frequency contribute to the dielectric loss due to conductivity?
No
At Neel temperature Susceptibility is:
maximum
With respect to dc motors, what do you call the losses in armature and series field winding
direct load loss
Materials which lack permanent dipoles are called:
Diamagnetic
What is the approximate percentage of volatile matter in coal?
25 – 35 %
In a permanent magnet dc motor, can the method of varying the field current be used to control its speed?
No
Potential transformers are used to measure
high a.c. voltage
Two D.C. series motors are connected in series to produce a torque T. Now if the motors are connected in parallel, what will be the torque produced?
T/4
For arc heating, the electrodes are made of _____.
graphite
A PN junction is _______.
a rectifier
Zero power factor method for an alternator is generally used to determine
voltage regulation of alternator
Which electric discharge lamps gives highest lumens per watt?
Sodium vapor lamp
How many different speeds can be obtained in cascade control of two induction motors?
4
A three-phase power transformer is provided with star-delta connections. In order to protect against fault, connection for current transformer should be in _______.
delta-star
For active region operation of NPN transistor, emitter is _____ with respect to base
negative
A series resonant circuit implies unity power factor and ______ current
unity, maximum
Mho relay is used to protect _____ transmission lines
long
If supply frequency increases, the skin effect
increases
What is the percentage slip in case of synchronous motor?
zero
If a combination of HRC fuse and circuit breaker is used, the circuit breaker operates
under all abnormal currents
What is the practical permissible variation of frequency in power system?
± 3%
Distribution transformers are designed to have maximum efficiency nearly at
50% of full load
True or False: 1 Ampere-turn = 4π Gilberts
False
In a transmission line, if the load is suddenly increased in the receiving end of the system, the phase shift will:
Increase
In approximately how many cycles can a high-speed circuit breaker complete its operation?
3 to 8
Energy formation of Schottky defect in a metal is of the order of ______.
1 eV
For an alternator operating at no load before the fault occurs, voltage of the alternator |Eg| divided by the steady state current |I| (rms value) is known as:
(d – axis) synchronous reactance Xd
Why are direct-on-line starters not suitable for starting large dc motors?
Large voltage drop may occur
What will be the effect of a crock in the magnetic path of inductor?
Reduced inductance
What is the cause of output voltage produced across the crystal in Hall’s effect?
Movement of charge carriers towards one end
Why is the compensating winding provided in a dc motor?
To prevent commutator flash over
The change in dimensions during the process of magnetization is called ______.
magnetostriction
