Smart series MCQs set 8 for all electrical engineering tests for post of Junior engineer/SDO in WAPDA ,GEPCO jobs NTS, NTDC,MEPCO,IESCO,PESCO and all DESCOS
- Paschen’s law is associated with
A. Breakdown voltage
B. Ionization
C. Thermal radiations
D. None Ans. A - A Tesla coil is a
A. Cascaded transformer
B. Coreless transformer
C. High frequency resonant transformer
D. Low impedance transformer Ans. C - Van de Graaff generators are useful for
A. Very high voltage and low current applications
B. Very high voltage and high current applications Ans. A - The phenomenon of corona Is generally accompanied by
A. Bang
B. Hissing sound
C. Magnetic hum
D. All of above Ans. B - Which of the following is a polar dielectric?
A. Teflon
B. Quartz
C. Nylon
D. Polyethylene Ans. C - Polar dielectrics are normally used for
A. High frequencies
B. Microwaves
C. DC and power frequencies
D. None of above Ans. C - The moving system in the indicating instruments is subjected to
A. Deflecting torque
B. Damping torque
C. Controlling torque
D. All of above Ans. D - If there are three resistances in parallel which path current will chose
A. High resistance
B. High impedance
C. High conductance
D. None Ans. C - The basic requirement of a DC armature winding is that it must be
A. Closed one
B. Lap winding
C. Wave winding
D. Either B or C Ans. A
- Among the following damping method, the most effective and efficient damping is
A. Air friction
B. Fluid friction
C. Eddy current
D. All are equally efficient Ans. C - Capacitor start, capacitor run single phase induction motor is basically a
A. AC series motor
B. DC series motor
C. Two phase induction motor
D. Three phase induction motor Ans. C - A capacitor start single phase induction motor will usually have a power factor
A. 0.8 lagging
B. 0.8 leading
C. 0.6 leading
D. 0.6 lagging Ans. D - In ultrasonic welding the frequency range is generally A. 100-4000 cps
B. 4000 – 20,000 cps
C. 20,000 – 80,000 cps
D. 80,000 – 800,000 cps
E. 800,000 – 5,000,000 cps
Ans. B - kWh meter is a type of meter.
A. Recording
B. Digital
C. Integrating
D. None Ans. C - If resistance decreases with increasing temperature, the coefficient will be.
A. Positive
B. Negative
C. Zero
D. None Ans. B - Synchronous motor is operating on leading PF when the motor is
A. Over excited
B. Under excited
C. Non excited
D. None Ans. A
- Regarding skewing of motor bars in a squirrel cage induction motor (SCIM) which statement is false.
A. It prevents cogging
B. it increases starting torque
C. It produces more uniform torque
D. It reduces motor ‘hum’ during its operation Ans. B - If the series resistance increases in an unloaded Zener regulator, Zener current
A. Decreases
B. Stays the same
C. Increases
D. Equals the voltage divided by the Zener resistance Ans. A - If the load resistance increases in a Zener regulator, Zener current
A. Decreases
B. Stays the same
C. Increase
D. Equals the source voltage divided by the series resistance Ans. C - If the base supply voltage increases, the Q point moves
A. Down
B. Up
C. Nowhere
D. Off the load line Ans. B - Active power and apparent power are respectively represented by
A. kW and kVAR
B. kVAR and kVA
C. kVA and kVAR
D. kW and kVA Ans. D - For a consumer what is the most economical power factor?
A. 0.25-0.5 lagging
B. 0.25 – 0.5 leading
C. 0.85 – 0.95 lagging
D. 0.85 – 0.95 leading Ans. C - The primary reason for the low power factor is due to the installation of
A. DC motors
B. Synchronous motors
C. Induction motors
D. Commutator motors Ans. C
- The most suitable location for the power factor improvement device is
A. Near the electrical appliance which is responsible for the poor power factor
B. At the sending end
C. At receiving end in case of transmission lines
D. Both (a) and (c) Ans. D - In order to improve the power factor of equipment operating at lagging power factor, a capacitor is connected
A. In series with the equipment
B. In parallel with the equipment
C. In series-parallel with the equipment
D. Either (a) or (b) Ans. B - If the load resistance decreases in a Zener regulator, the series current
A. Decreases
B. Stays the same
C. Increases
D. Equals the source voltage divided by the series resistance Ans. B - The device associated with voltage-controlled capacitance is a
A. Light emitting diode
B. Photodiode
C. Varactor diode
D. Zener diode Ans. C - To isolate an output circuit from an input circuit, which is the device to use
A. Back diode
B. Optocoupler
C. Seven-segment indicator
D. Tunnel diode Ans. B - The danger of electric shock is maximum
A. During arcing
B. After arcing
C. While inserting electrode into the holder
D. None of above Ans. C - The average DC output voltage for a half-wave rectifier is 13.05 V. Average value for a full- wave rectifier will be A. 26.1
B. 28
C. 10
D. None of these Ans A - The major advantage of a photo-transistor as compared to a photo-diode is
A. Response to higher frequencies
B. AC operation
C. Increase sensitivity
D. Durability Ans. C - When transistors are used in digital circuits they usually operate the
A. Active region
B. Breakdown region
C. Saturation and cut off regions
D. Linear region Ans. C - Power amplifiers in high frequency applications are mainly used
A. As a switch
B. For amplification
C. As protective devices
D. Voltage Controller Ans. A - Input impedance of an inverting OP-AMP is
A. Zero
B. Infinity
C. 10Mohms
D. None of these Ans. B - Switching surge is
A. High voltage DC
B. High voltage AC
C. Short duration transient voltage
D. Hyperbolically dying voltage Ans. C - Insulators for high voltage applications are tested for
A. Power frequency tests
B. Impulse tests
C. Both (A) & (B)
D. None of above Ans. C - Transformers contribute to radio interference due to
A. Corona discharges in air
B. Internal or partial discharges in insulation
C. Sparking
D. Any of above Ans. D - Surge voltage originate in power systems due to
A. Lightening
B. Switching operations
C. Faults
D. Any of above Ans. D - The torque developed by a split phase motor is proportional to
A. Sine of angle between Im and Is
B. Cosine of angle between Im and Is
C. Main winding current, Im
D. Auxiliary winding current, Is Ans. A - The power factor of an alternator depends on
A. Load
B. Speed of rotor
C. Core losses
D. Armature loses Ans. A - A welding generator has characteristics.
A. Rising
B. Drooping
C. None of them
D. Linear Ans. B - A 4-pole, 12-slot lap-wound DC armature has two coil-sides/slots. Assuming single turn coils and progressive winding, the back pitch would be
A. 5
B. 7
C. 3
D. None of above Ans. B - If the load on a DC shunt motor is increases, its speed is slightly reduced due to
A. Increase in armature current
B. Increase in flux
C. Decrease in reactance
D. Decrease in back emf Ans. D - Frequency of voltage generated by an alternator having 4-poles and rotating at 1800 rpm is hertz.
A. 60
B. 7200
C. 120
D. 450
Ans. A - The main disadvantage of using short Pitch winding in alternators is, it
A. Reduces harmonics in the generated voltage
B. Reduces the total voltage around the armature coils
C. Produces asymmetry in the three phase windings
D. Increases Cu of end connections Ans. B - The efficiency and power factor of a Squirrel Cage induction motor increases in proportion to its
A. Speed
B. Mechanical load
C. Rotor torque
D. Voltage Ans. B - A 4-band resistor has Red, Black, Green, Blue bands, its resistance
A. 1 M ohms
B. 3 M ohms
C. 2 M ohms
D. None Ans. C - An AC waveform having DC equivalent value
A. Effective value
B. 0.707 peak value
C. Both A & B
D. None of above Ans. C - If V = 5 + 5 sin 100ft then what will be the average current value of half sine wave
A. 0
B. 5
C. 10
D. None Ans: B - Absence of skin effect, lower line cost, less corona effect are features of the which transmission system
A. High voltage direct current (HVDC)
B. AC transmission system
C. Subsurface distribution system
D. Both A & B
Ans. A
- Extra high voltage (EHV) transmission has which of the following advantages
A. Reduction in noise
B. Increase in transmission efficiency
C. Improves voltage regulation
D. All of these Ans. D - The purpose of comparator is to
A. Amplify an input voltage
B. Detect the occurrence of a changing input voltage
C. Maintain a constant output when the DC input voltage changes
D. Produce a change in input voltage when an input voltage equals the reference Ans. D - DOG-ACSR conductor has
A. 1 strand of steel 6 strand of aluminum
B. 6 strand of steel 1 strand of aluminum
C. 6 strand of steel 7 strand of aluminum
D. 7 strand of steel 6 strand of aluminum Ans. D - Manufacturers measure the resistance of conductor at which temperature
A. 0
B. 20
C. 25
D. 27 Ans. C - Standard voltage supply in Pakistan is A. 220
B. 230
C. 240
D. 400
Ans. B - One horse power (hp) equals how many pounds per feet of engine
A. 22000 foot-pounds per minute
B. 22000 foot-pounds per second
C. 22000 foot-pounds per hour
D. 33000 foot-pounds per minute Ans. D - A piece of wire is stretched to double its length the resistance of wire becomes
A. 2R
B. 4R
C. R/2
D. R/4 Ans. B - One ton of air conditioner means
A. One ton of ice in 1 hour
B. One ton of ice in 12 hours
C. One ton of ice in 24 hours
D. None Ans. C - A 50-ohm resistance with 5% tolerance will have color code
A. Green, black, black
B. Green, black, black, gold
C. Green, black, brown, gold
D. Green, black, gold Ans. D - Cost saving of conductor in three phase over single phase A. 100%
B. 200%
C. 300%
D. 400%
Ans. C - In electrical traction, speed of DC motor can be varied by varying
A. Terminal voltage
B. Field current
C. 1st varying terminal voltage then field current
D. None Ans. B - In case the air gap in an induction motor is increased
A. The magnetizing current of rotor will decrease
B. The power factor will decrease
C. Speed of motor will increase
D. Windage losses will increase Ans. B - The number ofslip rings on a squirrel cage induction motor is usually
A. Two
B. Three
C. Four
D. None Ans. D - What is the dielectric strength of porcelain (kV Per inch)?
A. 20
B. 100
C. 203
D. 405
Ans. C - What is the dielectric strength of glass (kV Per inch)?
A. 355
B. 500
C. 600
D. 750
Ans. A - Cost of underground cables over overhead transmission lines is
A. Same
B. Double
C. More than double
D. None of above Ans. C - For percentage voltage-drop expression which of the following voltage is used
A. Sending end voltage
B. Receiving end voltage
C. System nominal voltage
D. Any of above Ans. C - Which gas is used in gas insulated substation?
A. Nitrogen
B. Sulphur hexachloride
C. Sulphur hexafluoride
D. Air Ans. C - The speed of squirrel-cage induction motor can be controlled by all of the following except
A. Changing supply frequency
B. Changing number of poles
C. Changing winding resistance
D. Reducing supply voltage Ans. C - In case of a three-phase induction motor, plugging means
A. Pulling the motor directly on line without a starter
B. Locking of rotor due to harmonics
C. Starting the motor on load which is more than the rated load
D. Interchanging two supply phases for quick stopping Ans. D - The speed of an alternator is changed from 3000 rpm to 1500 rpm, generated emf/phase will become
A. One fourth
B. Half
C. Double
D. Unchanged Ans. B - Alternators used in aircraft systems usually have frequency of
A. 50Hz
B. 60Hz
C. 25Hz
D. 400Hz Ans. D - Single phase induction motor torque at the instant of starting is
A. More than the rated torque
B. Equal to the rated torque
C. Zero
D. Less than the rated torque Ans. C - Which motor has the highest power factor?
A. Capacitor start motor
B. Capacitor run motor
C. Shaded pole motor
D. Repulsion motor Ans. B - The electric motor used in portable drill is
A. Capacitor run motor
B. Hysteresis motor
C. Universal motor
D. Repulsion motor Ans. C - The direction of rotation of universal motor can be reversed by reversing the flow of current through
A. Armature winding
B. Field winding
C. Both A & B
D. None of above Ans. C - Which system is used in industrial process for monitoring and self-correction?
A. Coal-slurry
B. Closed loop
C. Open loop
D. Feed forward Ans. B - 50 micro-Amp and 2k ohm voltmeter will show half scale deflection with voltage A. 0.05 V
B. 0.01 volt
C. 0.1 volt
D. 1 volt Ans. C - A magnetic shield or screen used to protect a delicate instrument should be made of which of the following materials
A. Plastic
B. Soft iron
C. Copper
D. Aluminum Ans. B - For generating 1MHz following oscillator could be used
A. Colpitts
B. Wein-bridge
C. RC phase shift
D. Hartley Ans. A - Dielectric strength in case of mica can be expected to be more than
A. 500kV/mm
B. 1500kV/mm
C. 2500kV/mm
D. 3500kV/mm Ans. A - Which impurity is present in liquid dielectric which strengthens the dielectric effect?
A. Dust
B. Dissolved gases
C. Moisture
D. Ionic impurity Ans. C - Circuit breaker is used for
A. Fault detection
B. Interruption
C. Both A & B
D. None Ans. B - What is the relative speed of stator and rotor fluxes?
A. Ns
B. Nr
C. Ns – Nr
D. 0 Ans. C - What is the synchronous speed of 960 rpm and 4% slip induction motor?
A. 1000 rpm
B. 900 rpm
C. 2000rpm
D. 3000rpm Ans. A - The principle of operation of a 3-phase induction motor is most similar that of a
A. Synchronous motor
B. Repulsion starts induction motor
C. Transformer with short secondary
D. Capacitor starts Ans. C - The three-phase induction motor with rotor circuit open will
A. Run normally
B. Make noise
C. Not run
D. Get over heated Ans. C - Poly phase field mean
A. Pulsating and stationary field
B. Pulsating and rotating field
C. Constant amplitude and rotating field
D. Constant amplitude and stationary field Ans. C - The main reason for generation of harmonics in a transformer could be
A. Fluctuating load
B. Poor insulation
C. Mechanical vibrations
D. Saturation of core Ans. D - Tertiary winding is used in which transformer
A. Star-delta
B. Delta-delta
C. Star-star
D. Any of above Ans. C - A power transformer has a single primary winding and three secondary windings producing 5.0volts, 12.6 volts and 150 volts. Assuming similar wire sizes, which of the three secondary windings will have the highest measured DC resistance?
A. 5-volt winding
B. 150-volt winding
C. 12.6-volt winding
D. All will have equal resistance Ans. C - A 230 DC motor is run on 230 Volt AC supply then
A. It will run smoothly
B. It will stop
C. It will burn out
D. It will run with less efficiency and high sparks Ans D - A good dielectric should have all these parameters except
A. High mechanical strength
B. High thermal deterioration
C. High dielectric loss
D. Freedom from gaseous inclusion Ans. C - Corona effect can be identified by
A. Bushy sparks
B. Faint violet glow
C. Red light
D. Arcing between conductors and earth Ans. B - Van de Graff generator output voltage can be controlled by
A. Controlling the corona source voltage
B. Controlling the belt speed
C. Controlling the lower spray point
D. Any of above Ans. A - Which of following materials is not used in fuses?
A. Copper
B. Silver
C. Aluminum
D. Carbon Ans. D - Resistive type transducer is used in
A. Carbon microphone
B. Strain-gauge
C. Thermistor
D. All Ans. D - Speed of induction motor can be varied by varying
A. B. Frequency.
B. Voltage of supply
C. Both A & B
D. None Ans. C - Operation of induction motor above base speed can be done With
A. High voltage and high frequency
B. Constant voltage and high frequency
C. Constant frequency and high voltage
D. 3rd harmonics Ans. B - Rotating wheel electrode is used in –
A. Arc welding
B. Resistive spot welding
C. Resistive seam welding
D. Dielectric welding Ans. C
Electrical EngineeringI Smart Series MCQs COMPETITIVE EXAMS SET 9(801-900)