Electrical and Electronics Engineering : 2016

An equipotential surface is a surface in an electric field such that all points on it are at the

A)Same potential
B)Different potential
C)Different frequency
D)Same frequency

In a.c. voltage regulator with R-L load

A)the current leads the voltage
B)current will lead or lag the voltage depending on the L/R ratio
C)the voltage lags the current
D)the voltage leads the current

Load voltage in a d.c. chopper circuit is given by / d.c.

A)d.c. supply voltage /duty cycle
B)Duty cycle X d.c. supply voltage
C)Duty cycle/ d.c. supply voltage
D)1/(duty cycle X d.c. supply voltage)

A thermistor has a resistance of 3.98 Kilo Ω at 0 °C and 0.794 Kilo Ω at 50 °C. If the relation between resistance and temperature is RT = a RO e b/T, the value of constant b is

A)2845

B)1845

C)4845

D)3845

Zener breakdown occurs due to breaking of covalent bonds by the strong electric field set up in the depletion region by the

A)Reverse coupling
B)Reverse voltage
C)Forward current
D)Forward voltage

A strain gauge with a resistance of 250 Ω undergoes a change of 0.15 Ω during a test. The strain is 1.5 x 10-4. The gauge factor is

A)4
B)6
C)3
D)1

For a moving charge Q in the presence of both electric and magnetic fields, the total force on the charge is given by

A)F = Q(B + μ x E)
B)F = Q(E - μ x B)
C)F = Q(B - μ x E)
D)F = Q(E + μ x B)

In a 132kV circuit breaker the bushing to ground capacitance is 0.01 microFarad and the transformer inductance succeeding the circuit-breaker is 4H. What will be the voltage appearing across the poles of circuit-breaker as it breaks a magnetising current of 15A flowing in the transformer?

A)300 kV
B)144 kV
C)363 kV
D)282 kV

A 1000 kHz carrier is modulated with 800 Hz audio sine wave, the frequencies present in the output will be

A)1000, 1000.8 kHz
B)999.2, 1000.8 kHz
C)999.2, 1000 kHz
D)1000, 1800 kHz

Which of the following law states that the magnetic field intensity dH produced at a point P, by the differential current element Idl is proportional to the product of Idl and the sine of the angle α between the element and the line joining P to the element and is inversely proportional to the square of the distance R between P and the element?/

A)Ampere's circuit law
B)Gauss's law
C)Snell's law
D)Biot-Savart's law

Converting the signed decimal -1 to 8 bit 2's complement number will result in

A)000000 01
B)111111 10
C)111111 11
D)011111 11

Master-slave J-K flip-flop is used to

A)Eliminate race around condition
B)Improve its reliability
C)Reduce power dissipation
D)Increase its clock frequency

When is the READY signal sampled or checked by the 8085 microprocessor?

A)At the end of each machine cycle
B)At the 2nd state of every machine cycle
C)At the end of each instruction cycle
D)At the 1st state of every machine cycle

Two point charges - 4 μC and 5 μC are located at (1 , 0 , 3) and (1, 4, - 2) respectively, then the potential at (1, 0, 1) assuming zero potential at infinity will be (consider ε0 = 10-9/36π)

A)-9 kV
B)-6 kV
C)6 kV
D)9 kV

A 3-phase, half wave controlled rectifier is connected to a 220V source. If the delay angle is 45 degree and the load resistance is 10 Ohm, what will be the average power dissipation in SCR, if SCR has a forward voltage drop of 1 V?

A)2.5 W
B)4.5 W
C)1.5 W
D)3.5 W

A diffraction pattern of a cubic crystal of lattice parameter a = 3.16 A⁰ is obtained with monochromatic X-ray beam of wavelength 1.54 A⁰, the first line on this pattern was observed to have θ = 30⁰, the interplanar spacing will be

A)1.54 A⁰
B)3.1 A⁰
C)11.2 A⁰
D)9.3 A⁰

The induced dipole moment is proportional to the field strength and the proportionality factor αe is called

A)Electronic polarizability
B)Protonic polarizability
C)Electronic field strength
D)Nuclear polarizability

A complex wave of r.m.s. value 240 V has 20% 3rd harmonic content and 2% 5th harmonic content then the approximate r.m.s. value of the fifth harmonic will be

5.7 V
4.7 V
3.7 V
2.7 V

The impedance of a 100 Ω resistor in series with a 10 mH inductor in the s-domain will be

A) 10+1002 s Ω
B) 10+100−2s Ω
C) 100+10−2 s Ω
D) 100+102 s Ω

The addressing mode used in instruction MOV A, B is

A)Implied
B)Immediate
C)Direct
D)Register

Deep bar rotors are used in induction motors to increase

A)Full load torque
B)Full load current
C)Starting current
D)Starting torque

The series resonant circuit that has its minimum impedance, and thus maximum current, at the resonant frequency, is often described as

A)a reflector circuit
B)an acceptor circuit
C)a deflector circuit
D)a rejector circuit

An air core toroid has 500 turns, mean radius of 14 cm, cross sectional area of 6 cm2. The mmf is 2000 AT, then the approximate value of the field intensity inside the core will be

A)2273 AT/m
B)3273 AT/m
C)1273 AT/m
D)4273 AT/m

In signal generators energy is

A) created
B)generated using a generator
C)converted from a simple d.c. source into a.c. energy at some specific frequency
D)converted from a simple a.c. source into d.c. energy at some specific frequency

Two transformers A and B each rated for 40kVA have core losses of 500W and 250W respectively and full load copper losses of 500W and 750W respectively. Which transformer will be preferred to supply lighting loads with the following output pattern? Four hours: Full load, Eight hours: Half load, Remaining twelve hours: No load

A)Cannot be predicted
B)Either Transformer A or Transformer B
C)Transformer B only
D)Transformer A only

What is the value of duty cycle of the clock signal of 8086 ?

A)50%
B)66%
C)33%
D)20%

If a 3-phase induction motor is running at super synchronous speed for self excitation then the machine

A)Feeds reactive power to the mains
B)Draws reactive power from the mains
C)Feeds real power to the mains
D)Draws real power from the mains

The effect of the even symmetry on Fourier series is that the wave has

A)a constant term and cosine terms only
B)sine terms only
C)a constant term and sine terms only
D)a constant term only

The power loss due to hysteresis in the transformer core of 0.05 m3 volume at 50 Hz frequency having an area of the loop is 800 J/m3 will be

A)2000 W
B)4000 W
C)1000 W
D)500 W

For the given open loop transfer function of a servo system with unity feedback what will be the value of damping ratio? Given G(s)=5/{(s+3)(s+4)}

A)0.57
B)2.25
C)1.75
D)4

In a thyristor the junction temperature is 60 degree C. Thermal power flow between the junction and heat sink is 4W. What will be the thermal resistance between junction and heat sink, if the latter is at a temperature of 20 degree C? /

A)15 degree C/Watt
B)5 degree C/Watt /
C)10 degree C/Watt
D)20 degree C/Watt

In a shaded pole induction motor, shading coils are used to

A)Produce rotating magnetic field ,
B)Reduce windage losses
C)Protect against sparking
D)Reduce winding losses

The impulse response of an initially relaxed system is e^{-2t} u(t). To produce a response of te^{-2t} u(t) what must be the input?

A)e^{-2t} u(t)
B)e^{-t} u(t)
C)2e^{-t} u(t)
D)1/2e^{-2t} u(t)

The inverse Laplace Transform of (4s-5)/(s2 −s −2) will be / (4s-5)/(s2 −s −2)

A)e2t+3e−t
B)e2t+3et
C)e-2t+3e−t
D)e-2t+3et

What will be the reserve capacity of a power plant having maximum demand 90MW? Given plant capacity factor 0.45 and utilization factor 75%.

90 MW
30 MW
120 MW
60 MW

The magnetic pressure on a piece of magnetic material is well defined by the relation

A)2B2/μ0
B)μ0/ 2B2
C)B2/2μ0
D)2μ0/ B2

If B is the total number of branches of the graph and N is the number of nodes, then total number of links (L) should be

A)(B+N+1)
B)(B+N-1)
C)(B-N-1)
D)(B-N+1)

When an external voltage is applied to a p-n junction making the p-type material positive with respect to the n-type material, then the p-n junction is said to be

A)Voltage divider biased
B)Reverse biased
C)Forward biased
D)Fixed biased

In a two wattmeter method with unity power factor

A) readings of two wattmeters are equal and each reads half of the power
B) readings of two wattmeters are equal but opposite in sign
C) one wattmeter reads zero and other reads all the power
D) any value can be read by each wattmeter

Consider the following program.

MVI A, 75
MVI B, 25
ADD B
DAA
After executing the program, what will be the content of the accumulator?

A) 34
B) 9A
C) 90
D) 00

Which of the following algorithms calculates the amplitude and phase of each harmonic component from a set of time domain samples of the input complex wave signal?

A)Fast Fourier transformer
B)Discrete cosine transform
C)Amplitude transformer
D)Program transformation

If a piece of silver wire has a resistance of 1 Ω, then the resistance of manganin wire of one-third the length and one-third the diameter having specific resistance of manganin 20 times that of silver will be

A)60 Ω
B)30 Ω
C)90 Ω
D)20 Ω

While performing the open-circuit and short-circuit tests on a transformer to determine its parameters the status of the low voltage (L.V) and high voltage (H.V) will be such that

In Open circuit L.V is open and in short circuit H.V is shorted
In Open circuit H.V is open and in short circuit L.V is shorted
In Open circuit L.V is open and in short circuit L.V is shorted
In Open circuit H.V is open and in short circuit H.V is shorted

An auto-transformer having a transformation ratio of 0.8 supplies a load of 3kW. The power transferred conductively from primary to secondary is

0.6 kW
2.4 kW
1.5 kW
0.27 kW

The magnetizing current in a transformer is rich in

Third harmonics
Fifth harmonics
Seventh harmonics
Thirteen harmonics

A 2-phase, 4 pole permanent magnet stepper motor has a step of

90 degrees
45 degrees
30 degrees
22.5 degrees

A 200/100V, 50 Hz transformer is to be excited at 40 Hz from the 100V side. For the exciting current to remain the same, the applied voltage should be

150 V
125 V
100 V
80 V

The utility of delta-connected tertiary windings in star-star connected power transformer is that it

Makes supply available for small loads
Provides low reactance paths for zero sequence currents
Is used to suppress harmonic voltages
All of these

If a sinusoidal voltage source is connected to a power transformer, its no-load current would be

Sinusoidal and lagging the voltage by ninety degrees
Sinusoidal and lagging the voltage by less than ninety degrees
Rich in third harmonic and its fundamental would lag the voltage by ninety degrees
Rich in third harmonic and its fundamental would lag the voltage less than ninety degrees

The voltage regulation of a large transformer is mainly influenced by

No-load current and load power factor
Winding resistances and load power factor
Leakage fluxes and load power factor
Winding resistances and core losses

A 220/440 V, 50Hz, 5kVA single phase transformer operates on 220V, 40 Hz supply with secondary winding. Then

The eddy current loss and hysteresis loss of the transformer decrease
The eddy current loss and hysteresis loss of the transformer increase
The hysteresis loss of the transformer increases while eddy current loss remains the same
The hysteresis loss remains the same whereas eddy current loss decreases

Supply to one terminal of delta-star three-phase core type transformer which is on no-load fails. Assuming magnetic circuit symmetry, voltages on the secondary side will be

230, 230,115
230,115, 115
345, 115, 115
345, 0, 345

Keeping in view the requirement of parallel operation, which of the 3-phase connections given below are possible?

A) Delta-delta and delta-star

B) Delta-delta and star-delta

C) Star-star to delta-delta

D) Delta-star to star-delta

Auto transformer is used in transmission and distribution

A) When operator is not available

B) When iron losses are to be reduced

C) When efficiency considerations can be ignored

D) When the transformer ratio is small

A single phase transformer is to be switched to the supply to have minimum inrush current. The switch should be closed at

A) Maximum supply voltage

B) Zero supply voltage

C) 1/1.414 maximum supply voltage

D) 0.5 times maximum supply voltage

A 2500/250V, 25kVA transformer is connected as an auto transformer to give 2500/2750 V. Its rating would be

A) 250 kVA; 225 kVA is transformed conductively

B) 250 kVA; 225 kVA is transformed inductively

C) 275 kVA; 250 kVA is transformed inductively

D) 275 kVA; 250 kVA is transformed conductively

In a transformer the phase angle between primary and secondary terminal voltage is

A) 90⁰; primary voltage leading the secondary voltage

B) 90⁰; primary voltage lagging the secondary voltage

C) A few degrees, primary voltage leading the secondary voltage

D) A few degrees, primary voltage lagging the secondary voltage

The efficiency of transformer at full-load 0.85 pf lag is 95%. Its efficiency at full-load 0.85 pf lead will be

A) Less than 95%

B) More than 95%

C) 95%

D) 100%

On the two sides of a star/delta transformer

A) Voltages and currents are both in phase

B) Voltages and currents both differ in phase by 30⁰

C) Voltages differ in phase by 30⁰ but currents are in phase

D) Currents differ in phase by 30⁰ but voltages are in phase

A 2/1 ratio, two winding transformer is connected as an auto transformer. Its KVA rating as an auto transformer compared to a two-winding transformer is

A) Same

B) 1.5 times

C) 2 times

D) 3 times

A transformer on no-load is switched on to a source of voltage. It will draw a current which

A) The same as the steady-state magnetizing current

B) Several times the steady-state magnetizing current depending upon the initial state of the residual flux in the transformer core

C) Several times the steady-state magnetizing current depending upon the initial state of the residual flux in the transformer core

D) Twice the steady-state magnetizing current provided the core has no residual flux

Transformer excited from a sinusoidal voltage source will draw a no-load current which

A) Is sinusoidal and of the same frequency as the voltage source

B) Comprises the fundamental frequency (same as that of the voltage source) and the peaking third harmonic

C) Comprises the fundamental frequency and the depressing third harmonic

D) Is sinusoidal of frequency three times that of the voltage source

For a fixed primary voltage how does the secondary terminal voltage of a transformer change if the power factor of capacitive load rises from 0.7 to 0.9 with load current remaining fixed?

A. No change in voltage

B. Voltage decreases

C. Voltage rises

D. Voltage will rise, go through maximum and then decrease

For a fixed primary voltage how does the secondary terminal voltage of a transformer change if the power factor of inductive load is raised from 0.7 to 0.9 with load current remaining fixed?

A) No change in voltage

B) Voltage decreases

C) Voltage rises

D) Voltage will rise, go through maximum and then decrease

Hysteresis losses are directly proportional to the

A) Square of frequency and flux density to the power 1.6

B) Frequency and flux density to the power 1.6

C) The square of frequency and proportional to the square of flux density

D) Frequency and proportional to flux density

Power input to a transformer on no load at rated voltage comprises predominantly

A) Copper loss

B) Hysteresis loss

C) Core loss

D) Eddy current loss

Which of the following tests must be performed on a transformer to determine its leakage reactance

A) SC test only

B) OC test only

C) Both OC and SC tests

D) Test by an impedance bridge

The applied voltage of a certain transformer is increases by 50% while the frequency reduced to 50%. The maximum core flux density will be

A) Becomes three times

B) Becomes 1.5 times

C) Becomes half

D) Remains the same

Building steel core out of stampings reduces eddy current loss because it

A) Increases core resistivity

B) Increases the effective length of eddy currents paths thereby increasing effective resistance to the flow of eddy currents

C) Increases core permeability

D) Reduces the effective length of eddy current path, thereby reducing effective resistance to the flow of eddy currents.

A coil wound on magnetic core is excited from an AC voltage source. The source voltage and its frequency are both doubled. The eddy current loss in the core will become

A) Half

B) Remains same

C) Double

D) Four times

Which three phase connection can be used in a transformer to introduce a phase difference of 30 degree between its output and corresponding input line voltages?

Star-Star
Star- Delta
Delta-Delta
Delta-zigzag

A single phase transformer when supplied from 220V, 50 Hz has eddy current loss of 50 W. If the transformer is connected to a voltage of 330V, 50 Hz, the eddy current loss will be

A) 168.75 W

B) 112.5 W

C) 75 W

D) 50 W

The power factor of a synchronous motor

A) Improves with increase in excitation and may even become leading at high excitations

B) Decreases with increase in excitation

C) Is independent of its excitation

D) Increases with loading for a given excitation

Generally the no-load losses of an electrical machine is represented in its equivalent circuit by

A) Parallel resistance with a low value

B) Series resistance with a low value

C) Parallel resistance with a high value

D) Series resistance with a high value

The synchronous impedance method of finding the voltage regulation by a cylindrical rotor alternator is generally considered as

A) A pessimistic method because saturation is not considered

B) An optimistic method because saturation is not considered

C) A fairly accurate method even if power factor is not taken into account while determining synchronous impedance

D) A fairly accurate method when power factor is taken into account while determining synchronous impedance

A DC series motor is accidentally connected to a single phase AC supply. The torque produced will be

A) Of zero average value

B) Oscillating

C) Steady and unidirectional

D) Pulsating and unidirectional

Switched reluctance motor means

A) Salient pole synchronous motor without excitation winding

B) A stepper motor with salient poles

C) Synchronous motors with salient poles on stator and rotor

D) A stepper motor with closed loop control and with rotor position sensor

In case of auto transformer, which of the following statements are correct?

I. An auto-transformer requires less copper as compared to a conventional 2-winding transformer of the same capacity

II. An auto-transformer provides isolation between the primary and secondary windings

III. An auto-transformer has less leakage reactance as compared to the conventional 2-winding transformer of same capacity

Select the correct answer using the codes given below

A) 1,2 and 3

B) 1 and 2

C) 1 and 3

D) 2 and 3

A single-phase transformer when supplied from 220V, 50Hz has eddy current loss of 50W. if the transformer is connected to a voltage of 330V, 50Hz, the eddy current loss will be

A) 168.75W

B) 112.5W

C) 75W

D) 50W

The torque of a reluctance motor can be effectively increased by

A) Increasing reluctance of the magnetic circuit along the direct axis

B) Decreasing the reluctance of the magnetic circuit along the quadrature axis

C) Increasing the ratio of the quadrature axis reluctance to direct axis reluctance

D) Decreasing the ratio of quadrature axis reluctance to direct axis reluctance

In a shaded pole induction motor, the rotor runs from the

A) Shaded portion to the unshaded portion of the pole while the flux in the former leads that of the latter

B) Shaded portion to the unshaded portion of the pole while the flux in the former lags that in the latter

C) Unshaded portion to the shaded portion while the flux in the former leads that it in the latter

D) Unshaded portion to the shaded portion while the flux in the former lags that in the latter

Skewing of the rotor in a three-phase squirrel-cage induction motor reduces

A) Noise, parasitic torque, starting torque and pullout torque

B) Noise and parasitic torque, but increases starting torque and pull out torque

C) Noise and pullout torque, but increases parasitic torque and starting torque

D) Noise, parasitic torque and starting torque, but increases pullout torque

The rotor power output of 3-phase induction motor is 15kW. The rotor copper losses at a slip of 4% will be

A) 600W

B) 625W

C) 650W

D) 700W

In cylindrical rotor synchronous machine, the phasor addition of stator and rotor mmfs is possible because

A) Two mmfs are rotating in opposite direction

B) Two mmfs are rotating in same direction at different speed

C) Two mmfs are stationary with respect to each other

D) One mmf is stationary and the other mmf is rotating

Synchronous condenser means

A. A synchronous motor with capacitor connected across stator terminals to improve power factor

B. A synchronous motor operating at full load with leading power factor

C. An over-excited synchronous motor partially supplying mechanical load, and also improving power factor of the system to which it is connected

D. An over-excited synchronous motor operating at no-load with leading power factor used in large power stations for improvement of power factor

An induction motor when started on load does not accelerate up to full speed but runs at 1/7 th of the rated speed. The motor is said to be

A) Locking

B) Plugging

C) Crawling

D) Cogging

The advantage of the double squirrel-cage induction motor over single cage rotor is that its

A) Efficiency is higher

B) Power factor is higher

C) Slip is higher

D) Starting current is lower

A DC shunt generator when driven without connecting field winding shows an open circuit terminal voltage of 12V. when field winding is connected and excited, the terminal voltage drops to zero because

A) Field resistance is higher than critical resistance

B) There is no residual magnetism in the field circuit

C) The field winding is wrongly connected

D) There is a fault in armature circuit

Consider the following statements: The use of interpoles in dc machines is to counteract the

I. Reactance voltage
II. Demagnetizing effect of armature mmf in the commutating zone
III. Cross-magnetizing effect of armature mmf in the commutating zone
Which of these statement(s) is/are correct?

A) 1 &2

B) 2&3

C) 1&3

D) 3 alone