90 Most Common Electrical McQ with Answer
QNo.1 Power in a Three Phase Circuit =
- A. P = 3 V Ph I Ph CosФ
- B. P = √3 V L I L CosФ
- C. Both 1 & 2.
- D. None of The Above
QNo.2 Earthing is necessary to give protection
against
- A. Danger of electric shock
- B. Voltage fluctuation
- C. Overloading
- D. High temperature of the conductors
QNo.3 Best practicable material for a fuse
wires is
- A. Aluminum
- B. Copper
- C. Iron
- D. Tin
QNo.4 Synchronous speed of a 3 phase, 4 pole,
50Hz induction motor is
- A. 1500 rpm
- B. 1440 rpm
- C. 3000 rpm
- D. 2880 rpm
QNo.5 What is maximum value of power factor?
- A. 0.5
- B. 1
- C. 1.5
- D. 0.95
QNo.6 Unit of magnetic flux is
- A. Weber
- B. Ampere - turn
- C. Tesla
- D. Coulomb
QNo.7 For cost and safety the outdoor
substations are installed for voltages above
- A. 11 KV
- B. 33 KV
- C. 66 KV
- D. 132 KV
QNo.8 Which of the following motors is used in
ceiling fan?
- A. Universal motor
- B. Synchronous motor
- C. Series moto
- D. Induction motor
QNo.9 Selection of fuse is based on
- A. Steady load
- B. Fluctuating load
- C. A & B
- D. None of these
QNo.10
PVC stands for
- A. Polyvinyl chloride
- B. Post varnish conductor
- C. Pressed and varnished cloth
- D. Positive voltage conductor
QNo.11 Transformer action requires a
- A. constant magnetic flux
- B. increasing magnetic flux
- C. Alternating Magnetic Flux
- D. alternating electric flux.
QNo.12 Speed of dc motor is directly
proportional to ___ and inversely proportional to:
- A. flux, back emf
- B. current, back emf
- C. back emf, flux
- D. back emf, voltage
QNo.13 If the thickness of laminations is
increased in a transformer, then
- A. the eddy current loss decreases.
- B. the eddy current loss increases.
- C. the hysteresis loss decreases.
- D. the hysteresis loss increases.
QNo.14 Iron losses of a machine are
- A. directly proportional to flux density
- B. directly proportional to the square of flux density
- C. inversely proportional to flux density
- D. inversely proportional to the square of flux density.
QNo.15
When two resistors are connected in series total resistance is 8Ω and then connected in
parallel, equivalent resistance is 2Ω. Values of resistances are:
- A. 5Ω and 3Ω
- B. 6Ω and 2Ω
- C. 4Ω and 4Ω
- D. 7Ω and 1Ω
QNo.16 ..........theorem is quite useful when
the current in one branch of a network is to be determined or when the current
in an added branch is to be calculated.
- A. Norton
- B. Thevenin
- C. Superposition
- D. Maximum Power Transfer
QNo.17 Circuit breakers work
- A. constantly
- B. only once
- C. when there is resistance
- D. when there is magnetic
QNo.18 A
closed path made by several branches of the network is known as
- A. Branch
- B. Loop
- C. Circuit
- D. Junction
QNo.19 The superposition theorem is applicable
to
- A. Voltage only
- B. Current only
- C. Both current and voltage
- D. Current, voltage and power
QNo.20 .........theorem is particularly useful
for analyzing communication networks.
- A. Milliman's Theorem
- B. Thevenin's Theorem
- C. Superposition Theorem
- D. Maximum Power Transfer Theorem
QNo.21 For induction motors, normally
- A. the rotor winding is connected to supply and the stator winding is short-circuited.
- B. the stator winding is connected to supply and the rotor winding is short-circuited.
- C. both the stator and the rotor windings are connected to supply.
- D. the stator winding is connected to supply and the rotor winding is open-circuited.
QNo.22
Which of the following is not a basic element of a transformer?
- A. core
- B. primary winding
- C. secondary winding
- D. mutual flux
QNo.23 In an oil filled transformer, oil is
provided for
- A. Cooling
- B. Insulation
- C. Lubricating
- D. Both cooling and insulation
QNo.24 Which among the following happens in a
low power factor?
- A. Large kVA rating of the equipment.
- B. Greater conductor size.
- C. Reduced handling capacity of the system.
- D. All of the above.
QNo.25 Fuses can serve upto a current of
- A. 25 A
- B. 50 A
- C. 75 A
- D. 100 A
QNo.26 Miniature circuit breaker is a small
- A. fuse
- B. magnetic switch
- C. electromagnetic switch
- D. two way switch
QNo.27 Application of Norton's theorem to a
circuit yields
- A. Equivalent current source and impedance in series
- B. Equivalent current source and impedance in parallel
- C. Equivalent impedance
- D. Equivalent current source
QNo.28 A
network which contains one or more than one source of e.m.f. is known as
- A. Linear network
- B. Non-linear network
- C. Passive network
- D. Active network
QNo.29
In a parallel circuit, current in each impedance is_____________
- A. Equal
- B. Different
- C. Zero
- D. Infinite
QNo.30 High tension cables are generally used
up to
- A. 11 KV
- B. 33 KV
- C. 66 KV
- D. 132 KV
QNo.31 Which type of motor is used in portable
drilling machine?
- A. Induction motor
- B. DC series motor
- C. Universal motor
- D. Shaded pole motor
QNo.32 Transformers are rated in:
- A. KV
- B. KVA
- C. KW
- D. KVAR
QNo.33 Thevenin's resistance R th is found
- A. By removing voltage sources along with their internal resistances
- B. By short-circuiting the given two terminals
- C. Between any two open terminals
- D. Between same open terminals as for E th
QNo.34 Two current carrying conductors placed
side by side, experience a force of attraction:
- A. When current direction of both conductors are same
- B. When current direction of both conductors are opposite
- C. Independent of the direction of currents
- D. Only when one conductor is carrying current
QNo.35
In a three phase, delta connection ——-
- A. line current is equal to phase current
- B. Line voltage is equal to phase voltage
- C. None of the above
- D. Line voltage and line current is zero
QNo.36 A circuit breaker is
- A. power factor correcting device
- B. a device to neutralize the effect of transients
- C. a waveform correcting device
- D. a current interrupting device.
QNo.37 The voltage rating of the transformer in
a pole-mounted Sub Station is.............
- A. 11 KV / 400 V
- B. 11 KV / 240 V
- C. 33 KV / 400 V
- D. None of the above
QNo.38 The insulating material for a cable
should have
- A. Low cost
- B. High dielectric strength
- C. High mechanical strength
- D. All of the above
QNo.39
Transformer-core laminations are made of
- A. cast iron
- B. wrought iron
- C. silicon steel
- D. cast steel.
QNo.40 When two batteries are connected in
parallel, it should be ensured that
- A. they have same e.m.f
- B. they have same make
- C. they have same ampere-hour capacity
- D. they have identical internal resistance
QNo.41
Norton's equivalent resistance is the ..............as Thevenin's
equivalent resistance.
- A. Not same
- B. Same
- C. Both A and B
- D. None of the above
QNo.42
Pressure cables are generally not used beyond
- A. 11 KV
- B. 33 KV
- C. 66 KV
- D. 132 KV
QNo.43 Fusing factor should be
- A. Equal to zero
- B. Less than one
- C. Equal to one
- D. More than one
QNo.44 In case of induction motor, Star I Delta
starter is used
- A. To prevent the motor from tripping
- B. Because it connects motor automatically in Delta winding
- C. To save the cost of H R C fuses
- D. None
QNo.45
While Thevenizing a circuit between two terminals, V th is
equal to
- A. Short-circuit terminal voltage
- B. Open-circuit terminal voltage
- C. Net voltage available in the circuit
- D. E.M.F. of the battery nearest to the terminals
QNo.46 Effective capacitance of capacitors
connected in series, is
- A. C = C 1 + C 2 + C 3 + C 4 +……
- B. 1/C = 1/C 1 +1/C 2 + 1/C 3 + 1/C 4 +……
- C. C = 1/C 1 + 1/C 2 + 1/C 3 + 1/C 4 +……
- D. C = 1/C 1 – 1/C 2 + 1/C 3 – 1/C 4 +……
QNo.47
The net power in a series R-C circuit is
- A. Zero
- B. Positive
- C. Negative
- D. None of these
QNo.48 H.R.C. fuses has
- A. High rating of current
- B. High rupturing capacity
- C. High resistance capacity
- D. None of these
QNo.49
An ideal transformer has maximum efficiency when
- A. copper losses are equal to iron losses
- B. copper losses are less than iron losses
- C. copper losses are more than iron losses
- D. copper losses and iron losses are equal to windage losses
QNo.50 The function of shunt in an ammeter is
to
- A. By pass the current
- B. Increase the sensitivity of the ammeter
- C. Increase the resistance of ammeter
- D. None of the above
QNo.51 For a star connected three phase AC
circuit ———
- A. Phase voltage is equal to line voltage and phase current is three times the line current
- B. Phase voltage is square root three times line voltage and phase current is equal to line current
- C. Phase voltage is equal to line voltage and line current is equal to phase current
- D. None of the above
QNo.52 Capacitor does not allow the sudden
change of
- A. current
- B. voltage
- C. power
- D. None of the above
QNo.53 In case of Inductive circuit, Frequency
is ___________ Proportional to the Current.
- A. Directly
- B. Inversely
- C. No Effect
- D. Double
QNo.54 A polyphase system is generated
by______?
- A. Having two or more generator windings separated by equal electrical angle.
- B. Having generator windings at equal distances
- C. None of the above
- D. A and C
QNo.55 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
QNo.56 Which, among the following is the
correct expression for impedance?
- A. Z=Y
- B. Z=1/Y
- C. Z=Y 2
- D. Z=1/Y 2
QNo.57 In a parallel circuit, we consider
_____________ instead of impedance.
- A. Resistance
- B. Capacitance
- C. Inductance
- D. Admittance
QNo.58 Admittance is the ___ of conductance and
suspectance.
- A. Arithmetic mean
- B. Arithmetic difference
- C. Vector sum
- D. Reciprocal
QNo.59 Moving Iron volt meter reads ___ value.
- A. Peak
- B. rms
- C. Average
- D. Peak to peak
QNo.60 Conduit pipes are normally used to
protect ________ cables.
- A. Unsheathed cables
- B. Armoured
- C. PVC sheathed cables
- D. All of the above
QNo.61 Inductor does not allow the sudden
change of
- A. Current
- B. Voltage
- C. Power
- D. None of the above
QNo.62 Ammeter shunt is ___ resistance.
- A. High
- B. Medium
- C. Low
- D. Very high
QNo.63 Which of the following information
available on name plate of a motor?
- A. HP rating
- B. RPM
- C. Frame model
- D. All of the above
QNo.64 Ward-Leonard system is used for:
- A. Voltage regulation of transformer
- B. DC motor speed control
- C. Excitation of alternator
- D. Voltage regulation of alternator
QNo.65 The insulating material for cables
should
- A. Be acid proof
- B. Be non-inflammable
- C. Be non-hygroscopic
- D. Have all above properties
QNo.66 Superposition theorem can be applied
only to circuits having
- A. Resistive elements
- B. Passive elements
- C. Non-linear elements
- D. Linear bilateral elements
QNo.67
In non-linear network does not satisfy
- A. Superposition condition
- B. Homogeneity condition
- C. Both homogeneity and superposition condition
- D. Homogeneity, superposition and associative condition
QNo.68 The power factor of pure resistive
circuit is
- A. Zero
- B. Leading
- C. Lagging
- D. Unity
QNo.69
___ helps to find out the direction of current in the conductor of a generator
- A. Cork screw rule
- B. Right hand thumb rule
- C. Fleming’s left hand rule
- D. Fleming’s right hand rule
QNo.70 Use of Earth Leakage Circuit Breaker is
advisable for
- A. human safety
- B. Ease to reset when trips
- C. Protecting from short-circuit
- D. None
QNo.71 The fault clearing time of a circuit
breaker is usually
- A. few minutes
- B. few seconds
- C. one second
- D. few cycles of supply voltage.
QNo.72 In an ammeter the shunt resistance
usually ..... meter resistance
- A. Equal to
- B. Less than
- C. Greater than
- D. Of any value
QNo.73 Form factor =
- A. rms value / average value
- B. average value / rms value
- C. rms value / peak value
- D. peak value / rms value
QNo.74 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
QNo.75 _________ cables are used for 132 kV
lines.
- A. High tension
- B. Super tension
- C. Extra high tension
- D. Extra super voltage
QNo.76 Open circuit test on a transformer is
conducted to obtain
- A. the leakage impedances
- B. the ohmic loss
- C. hysteresis loss only
- D. core loss only
QNo.77 A
passive network is one which contains
- A. Only variable resistance
- B. Only some sources of e.m.f. in it
- C. Only two sources of e.m.f. in it
- D. No source of e.m.f. in it
QNo.78 In Transformer, oil is used for
- A. Cooling the Transformer
- B. Providing insulation to Transformer winding and for cooling the Transformer
- C. Lubricating the Transformer
- D. None
QNo.79 Two wattmeter method of power
measurement is suitable for:
- A. balanced load only
- B. unbalanced load
- C. both balanced and unbalanced load
- D. delta connected load
QNo.80 The time taken by an alternating
quantity to complete one cycle:
- A. Time period
- B. Frequency
- C. Angular velocity
- D. Time constant
QNo.81 Liquid type H.R.C. fuses are used upto a
voltage of
- A. 33 kV
- B. 66 kV
- C. 132 kV
- D. 200 kV
QNo.82 A network has 4 nodes and 3 independent
loops. What is the number of branches in the network ?
- A. 5
- B. 6
- C. 7
- D. 8
QNo.83 Superposition theorem is not applicable
for
- A. Voltage calculations
- B. Bilateral elements
- C. Power calculations
- D. Passive elements
QNo.84 Which is active component?
- A. Capacitor
- B. Transistor
- C. Inductor
- D. Resistor
QNo.85 The capacity of a battery is expressed
in terms of
- A. current rating
- B. voltage rating
- C. ampere-hour rating
- D. none of the above
QNo.86 Which of the following is an AC motor?
- A. Slip ring motor
- B. Synchronous motor
- C. Squirrel cage Induction motor
- D. All of the above
QNo.87 Fuse wire should possess
- A. High specific resistance and high melting point
- B. High specific resistance and low melting point
- C. Low specific resistance and low melting point
- D. Low specific resistance and high melting point
QNo.88 D.C. motor starters are used
- A. to increase the starting torque.
- B. to limit the starting current.
- C. both (a) and (b).
- D. none of the above.
QNo.89
While considering hysteresis loss in a transformer, under which of the
following the loss will not increase?
- A. when flux density is increased by 10%
- B. When thickness of lamination is caused by 10%
- C. When frequency is increased by 10%
- D. When both thickness and frequency are increased by 10%.
QNo.90 H.R.C fuse is
- A. A ceramic body having metal end caps
- B. A wire of platinum
- C. A heavy cross-section of copper or aluminum
- D. A ceramic tube having carbon rod inside it.