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BSNL TTA 

Question Paper-2007

Electrical Engineering

Q.1.In a D.C. generator, if the brushes are given a small amount of forward shift, the effect of armature is

• Totally demagnetizing
• Totally magnetizing
• Partly demagnetizing and partly cross magnetizing
• Totally cross magnetizing

Q.2.The air gap between stator and armature of an electric motor is kept as small as possible

• To get a stronger magnetic field
• To improve the air circulation
• To reach the higher speed of rotation
• To make the rotation easier.

Q.3.Two series motors are coupled. One motor runs as generator & other as motor.The friction losses of the two machines will be equal when

• Both operates at same voltage
• Both have same back emf
• Both have same speed
• both have same excitation

Q.4.Plugging of D.C. motor is normally executed by

• Reversing the field polarity
• Reversing the armature polarity
• Reversing both the armature and field polarity
• Connecting a resistance across the armature.

Q.5.Transformer oil transformer provides

• Insulation and cooling
• Cooling and lubrication
• Lubrication and insulation
• Insulation, cooling and lubrication

Q.6.Leakage fluxes of transformer may be minimized by

• Reducing the magnetizing current to the minimum
• Reducing the reluctance of the iron core to the minimum
• Reducing the number of primary and secondary turn to the minimum
• Sectionalizing and interleaving the primary and secondary windings

Q.7.Electric power is transformed upon one coil to other coil in a transformer

• Electrically
• Electro Magnetically
• Magnetically
• Physically

Q.8.The most suitable and economical connection for small high voltage transformer isa.

• Star- Delta connection
• Delta- Delta connection
• Delta- Star connection
• Star- Star connection

Q.9.An alternator is said to be over excited when it is operating at

• Unity power factor
• Leading power factor
• Lagging power factor
• Either lagging or leading power factor

Q.10.In an A.C. machine, the armature winding is kept stationary while the field winding is kept rotating for the following rason

• Armature handles very large currents and high voltages
• Armature friction involving deep slots to accommodate large coils is easy if armature is kept stationary
• Ease of cooling the stator than rotor
• None of the above.

Q.11.In a synchronous motor, the torque angle is the

• Angle between the rotating stator flux and rotor poles
• Angle between the magnetizing current and back emf
• Angle between the supply voltage and back emf
• None of the above

Q.12.A 3-phase synchronous motor is said to be "floating" when it operates

• On no load and without loss
• On constantly varying load
• On pulsating load
• On high load and variable supply voltage

Q.13.Speed of synchronous motor depends upon

• Number of poles
• Supply frequency
• Both (a) and (b)
• Neither (a) nor (b)

Q.14.Imbalance in the shaft of an induction motor occurs due to

• Slip rings
• Overheating of winding
• Non uniform of air gap
• Rigid construction

Q.15.Squirrel cage induction motor has

• Zero starting torque
• Very small starting torque
• Medium starting torque
• Very high starting torque

Q.16.The principle of operation of a 3-phase induction motor is similar to that of a

• Synchronous motor
• Repulsion - start induction motor
• Transformer with a shorted secondary
• Capacitor - start, induction - run motor

Q.17.The speed/load characteristics of a universal motor are similar to those

• D.C. shunt motor
• D.C. series motor
• A.C. motor
• None of the above

Q.18.Single phase A.C. motor generally used for vacuum cleaners is

• Universal motor
• Repulsion motor
• Hysteresis motor
• Reluctance motor

Q.19.Buchholz relay is used for the protection of

• Switch yard
• Transformers
• Alternators
• Transmission lines

Q.20.The type of braking used in traction system is

• Mechanical braking
• Electro - pneumatic braking
• Vacuum braking system
• All the above

Q.21.The function of processing zener diode in a UJT circuit used for triggering of SCRs is to

• Expedite the generation of triggering pulses
• Delay the generation of triggering pulses
• Provide a constant voltage to UJT to prevent erratic firing
• Provide a variable voltage to UJT as the source voltage changes

Q.22.The frequency of a ripple in the output voltage of a 3 - phase semi converter depends upon

• Firing angle and load resistance
• Firing angle and supply frequency
• Firing angle and load inductance
• Only on load circuit parameters

Q.23.The SCR is turned off when the anode currents falls below

• Forward current rating
• Break - over voltage
• Holding current
• Latching

Q.24.V-I characteristics of emitter of a UJT is

• Similar to CE with linear and saturation region
• Similar to FET with a linear and pinch of region
• Similar to tunnel diode in some respects
• Linear between the peak point and valley point

Q.25.A transformer works on

• DC
• AC
• AC & DC both
• Neither AC not DC

Q.26.Which of the following device is used in transformer?

• Tube light
• Electric heater
• Mobile phone
• Rectifier module

Q.27.Earth electrodes can be in the form of

• rods or piper
• stripes
• plates
• any of above

Q.28.Carbone or metal brushes are used in

• DC generators only
• AC generators only
• Both AC & DC generation
• None of above

Q.29.Energy is lost due to Joule's heating effects in winding of transformer. This is called

• Copper loss
• Eddy current loss
• Flux loss
• None

Q.30.In refrigeration cycle heat is lost in

• Cooling coil
• Condenser
• Compressor
• Expansion valve

Q.31.The power factor of AC circuit is

• R/X
• R/Z
• Z/R
• Zero

Q.32.Silicon controlled output is good if ripple factor is

• Switch
• Transformer
• Amplifier
• None of above

Q.33.The rectifier output is good if ripple factor is\

• More
• Less
• Constant
• None of above

Q.34.Protective relays can monitor large AC current by means of

• Current transformer
• Potential transformer
• Micro transformer
• None of above

Q.35.The combines AM of two similar batteries connected in parallel is:

• halved
• doubled
• remain constant
• none of above

Q.36.The current in circuit having 5 V EMI source and 10 Ohm resistance is:

• 2 Amp
• 50 Amp
• 5 Amp
• ½ Amp

Q.37.The chopper is a device to change

• Voltage
• Current
• Frequency
• None of these

Q.38.The power consumption, in case of centrifugal loads (like pump, fan, blower etc) is
proportional to:

• speed
• square of speed
• cube of speed
• none of these

Q.39.Which of these need to be measured after rewinding the motor:

• no load current
• air gap
• winding resistance
• all of the above

Q.40.Five percent increase in supply frequency will change the synchronous speed of motor by:

• -5%
• +5%
• -10%
• +10%

Q.41.Which of the following is the best inverter?

• square wave inverter
• sine wave inverter
• pure sine wave inverter
• triangular wave inverter

Q.42.For driving a motor in a tape recorder or record player, the motor used is generally:

• a synchronous motor
• a hydraulic motor
• an induction motor
• a dc series motor

Q.43.The DC motor starter used with a constant speed shunt motor is:

• 2 point starter
• 3 point starter
• 4 point starter
• 5 point starter

Q.44.A commutator in a DC motor converts

• AC to DC
• DC to AC
• Both AC to DC and DC to AC
• None of these

Q.45.Two transformers running in parallel will share the load according to their:

• leakage reactance
• pu impedance
• efficiency
• rating

Q.46.The size of the Earth Wire is determined by:

• the ampere capacity of the service wires
• the atmospheric conditions
• the voltage of service wires
• none of these

Q.47.The function of lightning arrester is:

• to limit the short circuit fault current
• to provide path to high voltage surge to earth
• to reduce arcing
• none of these

Q.48.Surge protector provide:

• high impedance to normal voltage
• low impedance to surge
• both (a) and (b)
• none of these

Q.49.Earthing is necessary to give protection against

• voltage fluctuation
• overloading
• danger of electric shock
• high temperature of conductors

Q.50.The primary function of fuse is to

• protect the appliance
• open the circuit
• prevent excessive current
• protect the line

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ELECTRICAL/ ELECTRONICS ENGINEERING 

Model Exam Paper

For Various Competitive Examinations

Q.1.The main scale of a vernier calliper is ruled in 1 mm units.The vernier scale is 49 mm long and divided in 50 units. The resolution of the vernier calliper is

• 0.002 mm
• 0.005 mm
• 0.01 mm
• 0.02 mm

Q.2.A frequency counter with a gating time of 50 ms counts 1254 cycles of an input square wave. The frequency of the input wave is

• 39.87 Hz
• 62.70 Hz
• 1.254 kHz
• 25.08 kHz

Q.3.A data acquisition system with the input range of ± 5.0 V has a 12-bit ADC in it.The resolution of the system is approximately

• 0.24 mV
• 0.48 mV
• 1.22 mV
• 2.44 mV

Q.4.Watt meters are based on the principle of

• permanent magnet moving coil meter
• electrodynamic meter
• electrostatic meter
• moving iron meter

Q.5.The resolution of a Gray-coded optical shaft encoder with 10-bit output is approximately

• 0.098°
• 0.176°
• 0.225°
• 0.352°

Q.6.The unit of the permittivity of free space (E0) is

• C2 N–1 m–2
• C2 N m2
• C–2 N m2
• C–2 N m–1

Q.7.A positively charged object is placed in the center of a room with a uniform magnetic field. If the magnetic field is pointing east, the object will

• move east
• move north
• move south
• remain stationary

Q.8.The input impedance of a quarter-wave long short-circuited lossless transmission line is

• purely reactive
• purely resistive
• infinite
• dependent on the characteristic impedance of the line

Q.9.For a plane wave propagating in the free space,

• the electric and magnetic fields are in parallel to the direction of propagation there is no field in the direction of propagation
• the electric and magnetic fields are out of phase
• the magnetic field amplitude is inversely proportional to the electric field amplitude
• None of these

Q.10.Which of the following materials has the largest energy gap between the conduction band and the valence band?

• Gold
• Silicon
• Doped germanium
• Porcelain

Q.11.The area of hysteresis loop in a ferromagnetic material is a measure of

• loss of energy
• loss of magnetic domain
• loss of magnetic dipole
• loss of eddy currents

Q.12.If a tetra- valent impurity is added to a pure silicon crystal at room temperature, it becomes

• a p-type semiconductor
• an n-type semiconductor
• an npn-type semiconductor.
• an insulator

Q.13.Unregulated dc power supply is not in need of

• Diode
• Transformer,
• Zener diode
• filter

Q.14.The eigen values of a skew-symmetric matrix are

• always zero
• always pure imaginary
• either zero or pure imaginary
• always real

Q.15.At room temperature, a possible value for the mobility of electrons in the inversion layer of a silicon n-channel MOSFET is

• 450 cm2/V-s
• 1350 cm2/V-s
• 1800 cm2/V-s
• 3600 cm2/V-s

Q.16.For parallel RLC circuit, which one of the following statements is NOT correct?

• The bandwidth of the circuit deceases if R is increased
• The bandwidth of the circuit remains same if L is increased
• At resonance, input impedance is a real quantity
• At resonance, the magnitude of input impedance attains its minimum value.

Q.17.Q-meter works on the principle of

• series resonance
• parallel resonance
• mutual inductance
• self inductance

Q.18.Which one of the following is a ceramic insulator?

• Mica
• Porcelain
• Liquid crystal
• Synthetic fiber

Q.19.Which one of the following represents a direct band-gap material?

• Si
• Ge
• GaP
• GaAs

Q.20.Which one of the following statements is NOT true?

• Rochelle salt exhibits ferroelectric property.
• Spontaneous polarization is a characteristic property of ferroelectric material.
• Spontaneous polarization of ferroelectric materials usually vanishes below ferroelectric Curie temperature.
• Ferroelectric materials exhibit hysteresis effect.

Q.21.Which one of the following diodes contains a metal-semiconductor junction?

• Tunnel diode
• Zener diode
• Schottky diode
• Gunn diode

Q.22.The most appropriate value (in Ohm) of the radiation resistance of a quarter wave monopole antenna is

• 36.5
• 50
• 73
• 120

Q.23.Which one of the following is an active transducer?

• Photo-voltaic cell
• Strain gauge
• Photo-emissive cell
• Synchro 

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BSNL TTA Model Exam Papers

Microwave & Communication

Q.1The most common modulation system used for telegraphy is

• FSK
• PSK.
• PCM
• single tone modulation
• Two tone modulation

Q.2.VSB is an abbreviation of vestigal sideband, is derived by filtering

• DSB
• AM
• either (a) or (b)
• PM

Q.3.In practical waveguide act as

• low pass filter
• high pass filter
• band pass filter
• band stop filter

Q.4.The Hartely law states that

• The maximum rate of information transmission depends on the depth of modulation
• The maximum rate of information depends on the channel bandwidth.
• Only binary codes may be used
• Redundancy is essential

Q.5.The FM signal with, a modulation index mf is passed through a frequency tripler. The wave in the output of the tripler will have a modulation index of

• mf/9
• mf/3
• mf
• 3 mf
• 9mf

Q.6.Due to curvature of earth, microwave repeaters are placed at distance of about

• l0 Km
• 50 Km
• 200 Km
• 500 Km

Q.7.In high power AM transmission, modulation is done at

• Buffer stage
• Oscillator stage
• RF power stage
• If stage

Q.8.Which of the following is not a microwave generation source?

• Klystron
• Magnetron
• TWT
• Diode

Q.9.Companding is used

• In delta modulator to combat noise
• To limit amplitude in PCM transmitters.
• In PWM for working it with TDM
• To protect small signals in PCM from quantizing distortion
• In PCM to reduce the SNR

Q.10.In PCM system the SNR of the output signal increases

• Inversely with bandwidth
• Exponential with bandwidth
• With rate of sampling
• At low frequencies only

Q.11.Armstrong modulator generates

• Phase modulated signal
• Frequency modulated signal
• Both of these
• Pulse code modulated signal 
• AM and PCM signals

Q.12.A Klystron is a cavity acting as buncher and catcher is used as microwave tube for

• Guiding waves
• Velocity modulation
• frequency modulation
• impedance matching
• All of these

Q.13.Easily adjustable tuning component in a waveguide is

• plunger
• plunger and stub
• screw
• both (a) and (c)
• both (b) and (c)

Q.14.A ferrite is

• A non-conductor with magnetic properties
• A conductor with magnetic properties
• A semiconductors
• An insulator which attenuates magnetic fields
• A compound with good conductivity.

Q.15.Vacuum tubes eventually fail at microwave frequencies because of their

• Inter electrode capacitance
• Small series inductance
• Large shunt capacitance
• Short transit time
• Increased noise figure

Q.16.The biggest disadvantage the IMP ATT diode has is its

• Low Efficiency
• high noise
• Low BW
• inability to provide pulse operation
• low power handling ability

Q.17.An attenuator is used with TWT to

• prevent oscillations
• increase gain
• prevent saturation
• help bunching

Q.18.In AM transmission the frequency, which is not transmitted is

• carrier frequency
• audio frequency
• upper side frequency
• lower side frequency

Q.19.Maximum undistorted power output of a transmitter is obtained when its modulation is:

• more than 100%
• 100%
• less than 100%
• 50%

Q.20.The cut off frequency of a wave guide means

• lower frequencies will not be propagated
• it determines the dimensions of the wave guide
• frequency at which zero transmission takes place
• None of above

Q.21.FM broadcast band lies in

• VHF
• UHF
• SHF
• HF

Q.22.Automatic gain control is used

• to maintain the tuning correct
• to reduce the voltage of loud passage of music
• to maintain the same amount of output, when stations of different strength are received
• to increase the amplification at high frequencies

Q.23.The modulation system inherently is most noise resistant in

• SSB suppressed carrier
• FM
• PPM
• PCM

Q.24.An FM transmitter has maximum frequency deviation of 75 KHz and reproduces audio signal up to 15 KHz. Minimum channel width required, in KHz is

• 180
• 120
• 90
• 60

Q.25.The antenna efficiencies achieved in practice depend upon

• wave length
• impedance
• frequency
• none of above

Q.26.The process of compressing the digital codes at the transmitter and then expanding them back to their original form at receiver is known as

• Quantizing
• companding
• step sizing
• modulation

Q.27.TWT is basically

• an oscillator
• tuned amplifier
• wide band amplifier
• an audio amplifier

Q.28.In PPM, message resides in

• Pulses
• time location of pulse edges
• none of these
•  

Q.29.Digital transmission efficiency is given by

• information bits/total bits
• total bits/information bits
• redundant bits/information bits
• none of the above

Q.30.Which of the following pulse systems requires higher bandwidth

• PAM
• PDM
• PPM
• none of these

Q.31.The speed of BRI ISDN interface is

• 2B + D
• 2D + B
• 30B + D
• 30D + B

Q.32.In case of matched load

• Transmission is zero
• reflection is zero
• reflection is unity
• transmission is equivalent to reflection

Q.33.A signal of maximum frequency of 1 KHz is sampled at Nyquist Rate.The interval between two successive samples is:

• 50 micro seconds
• 100 micro seconds
• 500 micro seconds
• 1000 micro seconds

Q.34.Man made noise id caused by:

• Solar eruptions
• Distant Stars
• Lightning Discharges
• Arc discharge in electric machines

Q.35.In order to get back the original signal, it is necessary to use:

• low pass filter
• high pass filter
• band pass filter
• band reject filter

Q.36.The function of AM detector circuit is

• to rectify the input signal
• to discard the carrier
• to provide the audio signal
• All of the above

Q.37.At microwave frequencies, the size of antenna becomes

• very large
• large
• small
• very small

Q.38.To increase the Q factor of an induction, it wound with

• thicker wire
• thinner wire
• longer wire
• wire with heavy insulation

Q.39.For handling large microwave power, the best medium is

• coaxial line
• rectangular waveguide
• stripline
• circular wave guide

Q.40.The negative resistance in Gunn diode is due to

• electron transfer to a less mobile energy level
• high reverse bias
• electron domain formation at the junction
• tunneling across the junction

Q.41.Which of the following sinusoidal oscillator is preferred for microwave frequencies?

• resonant circuit oscillator
• RC phase shift oscillators
• negative resistance oscillators
• all of the above

Q.42.When electromagnetic waves are propagated in a waveguide

• they travel along the walls of the waveguide
• they travel through the dielectric without touching the walls
• they are reflected from the walls but do not travel along the walls
• none of above

Q.43.The AGC voltage in a radio receiver is proportional to

• the amount of modulation
• the amplitude of audio signal
• the amplitude of IF carrier
• none of these

Q.44.Which of the following pulse systems is preferred for communication in presence of noise?

• PAM
• PDM
• PPM
• none of above

Q.45.Wave guides are generally made of

• Cast iron or steel
• White metal or gun metal
• bronze or aluminium
• plastic or bakelite

Q.46.With 100% modulation,ratio of side band power to total power transmitted in an amplitude modulated wave is

• 2/3
• l/3
• l/2
• l/4

Q.47.In an AM wave with 100% modulation, the carrier is suppressed.The percentage of power saving will be

• 100%
• 50%
• 25%
• 66.7%

Q.48.Power factor of a purely resistive circuit is:

• zero
• one
• 0.5
• infinity

Q.49.In FM, the noise can be further decreased by

• decreasing deviation
• increasing deviation
• (c) keeping deviation constant
• (d) none of these

Q.50.The audio frequency range lies between

• 20 to 20,000 Hz
• 20 to 20,000 KHz
• 400 to 8,000Hz
• 500 to 5,000 Hz

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