ISRO Scientist or Engineer Electrical 2017

ISRO Scientist or Engineer Electrical 2017 - Question 1

Report

An inductance of one H carrying a current of two amperes will store the energy of

A

2 watts

B

2 joules

C

4 watts

D

4 joules

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ISRO Scientist or Engineer Electrical 2017 - Question 2

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The square waveform of current has following relation between r.m.s value and average value

A

r.m.s. value of current is greater than the average value

B

r.m.s. value of current is less than the average value

C

r.m.s. value of current is equal to the average value

D

There is no definite relation between the r.m.s. value and average value for a square wave

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ISRO Scientist or Engineer Electrical 2017 - Question 3

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Two numbers of 500 ohms one watt resistors are connected in parallel. Their combined resistance and wattage rating will be

A

250 ohms, 1 watt

B

250 ohms, 2 watts

C

1000 ohms, 2 watts

D

500 ohms, 2 watts

View Solution

ISRO Scientist or Engineer Electrical 2017 - Question 4

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In a long uniform coil of inductance 2L and associated resistance 2R ohms is physically cut in to two exact halves which are rewound in parallel. The resistance and inductance of the combination are

A

R and L

B

2R and 2L

C

R/2 and L/2

D

R/4 and L/4

View Solution

ISRO Scientist or Engineer Electrical 2017 - Question 5

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For transfer function of a physical two-port network

A

All zeros must lie only in the left half of the s-plane

B

All poles may lie anywhere in the s-plane

C

The poles lying on the imaginary axis must be simple

D

All the above

View Solution

ISRO Scientist or Engineer Electrical 2017 - Question 6

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The starting torque of a three phase induction motor can be increased by

A

Increasing rotor reactance

B

Increasing rotor resistance

C

Increasing stator resistance

D

None of the above

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ISRO Scientist or Engineer Electrical 2017 - Question 7

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The capacitor start-capacitor run single phase induction motor is operationally a

A

Single phase motor

B

Two phase motor

C

Three phase motor

D

A.C. series motor

View Solution

ISRO Scientist or Engineer Electrical 2017 - Question 8

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What would happen if the field of a D.C. shunt motor is opened?

A

Speed will be reduced

B

Continue to run normally

C

Speed will enormously increase damaging the motor

D

None of the above

View Solution

ISRO Scientist or Engineer Electrical 2017 - Question 9

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Equalizer rings in D.C. generator with lap windings are used for

A

Equal distribution of current at brush for sparkless commutation

B

Prevention of harmonics

C

Reduction of noise and vibration

D

Avoiding overhang

View Solution

ISRO Scientist or Engineer Electrical 2017 - Question 10

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The Buchholz relay is normally used to protect the

A

Alternators against all internal faults

B

Oil immersed transformers against all internal faults

C

Synchronous motors against all internal faults

D

Transmission lines against all short circuit faults

View Solution

ISRO Scientist or Engineer Electrical 2017 - Question 11

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The power transformer is a

A

Constant current device

B

Constant voltage device

C

Constant power device

D

Pulsating main flux device

View Solution

ISRO Scientist or Engineer Electrical 2017 - Question 12

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A change of 5% in supply voltage to an induction motor will produce a change of approximately

A

5% in the rotor torque

B

7.5% in the rotor torque

C

10% in the rotor torque

D

25% in the rotor torque

View Solution

ISRO Scientist or Engineer Electrical 2017 - Question 13

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If the supply frequency to the transformer is increased, the iron loss

A

Will increase

B

Will decrease

C

Will not change

D

May reach zero

View Solution

ISRO Scientist or Engineer Electrical 2017 - Question 14

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The maximum temperature permitted for class A insulation is

A

180 degree centigrade

B

105 degree centigrade

C

120 degree centigrade

D

None of the above

View Solution

ISRO Scientist or Engineer Electrical 2017 - Question 15

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Two transformers connected in parallel share load in the ratio of their KVA ratings, provided their ohmic impedance are

A

Equal

B

In direct ratio of their ratings

C

In inverse ratio of their ratings

D

Purely reactive

View Solution

ISRO Scientist or Engineer Electrical 2017 - Question 16

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The high frequency hum in the transformers is mainly due to

A

Loose laminations

B

Magnetostriction

C

Impurity in oil

D

Weakness of tank wall

View Solution

ISRO Scientist or Engineer Electrical 2017 - Question 17

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A 400/200 volts transformer has pu impedance of 0.05. The HV side voltage required to circulate full load current during short circuit test is

A

20 V

B

40 V

C

10 V

D

5 V

View Solution

ISRO Scientist or Engineer Electrical 2017 - Question 18

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Non-loading heat run test on transformers is performed by means of

A

SC test

B

OC test

C

Core balance test

D

Sumpner’s test

View Solution

ISRO Scientist or Engineer Electrical 2017 - Question 19

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A three phase induction motor is driving full-load torque which is independent of speed. If the line voltage drops to 90% of the rated value, % increase in motor copper losses

A

23%

B

-18%

C

123%

D

None of these

View Solution

ISRO Scientist or Engineer Electrical 2017 - Question 20

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A synchronous generator is feeding power to infinite bus bars at unity power factor. Its excitation is now increased. It will feed

A

The same power but at a leading power factor

B

The same power but at a lagging power factor

C

More power at unity power factor

D

Less power at unity power factor

View Solution

ISRO Scientist or Engineer Electrical 2017 - Question 21

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The steam input in to a turbogenerator connected to infinite bus is increased. Which of the events will take place?

A

The generator will feed more leading KVAR to bus bar and power angle will not change

B

The generator will feed more real power to bus bar and power angle will increase

C

The generator will feed more power to bus bar and power angle will decrease

D

The generator will feed more lagging KVAR to bus bar and power angle will not change

View Solution

ISRO Scientist or Engineer Electrical 2017 - Question 22

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In an ideal transformer, which of the following statement is correct?

A

no voltage drops in resistance or leakage reactance

B

mmf required to maintain main flux is small

C

no core loss

D

all the above are correct

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ISRO Scientist or Engineer Electrical 2017 - Question 23

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The voltage applied to a transformer primary is increased keeping v/f fixed. How will core loss and magnetizing current change?

A

Core loss will increase and magnetizing current remain same

B

Core loss will remain same and magnetizing current will remain same

C

Core loss will decrease and magnetizing current will increase

D

Core loss will remain same and magnetizing current will decrease

View Solution

ISRO Scientist or Engineer Electrical 2017 - Question 24

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Frequencies in the UHF range normally propagate by means of

A

Ground waves

B

Sky waves

C

Surface waves

D

Space waves

View Solution

ISRO Scientist or Engineer Electrical 2017 - Question 25

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Indicate the antenna that is not wideband

A

Discone

B

Folded dipole

C

Helical

D

Marconi

View Solution

ISRO Scientist or Engineer Electrical 2017 - Question 26

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The depth of penetration of a wave in a lossy dielectric increases with increasing

A

Conductivity

B

Permeability

C

Wavelength

D

Permittivity

View Solution

ISRO Scientist or Engineer Electrical 2017 - Question 27

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Copper behaves as a

A

Conductor always

B

Conductor or dielectric depending on field strength

C

Conductor or dielectric depending on frequency

D

Conductor or dielectric depending on the electric current density

View Solution

ISRO Scientist or Engineer Electrical 2017 - Question 28

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Assuming constant transmission efficiency, if voltage is increased ‘n’ times, the size of the conductor would be

A

Reduced to $$\frac{1}{n^2}$$ that of the original

B

Increased to $$n^2$$ that of the original

C

Reduced to $$\frac{1}{n}$$ that of the original

D

Increased to $$n$$ times that of the original

View Solution

ISRO Scientist or Engineer Electrical 2017 - Question 29

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Shunt conductance in overhead power transmission lines is primarily due to

A

Leakage over the insulators

B

Leakage over the conductors

C

Leakage over the poles

D

Leakage between ground and conductors

View Solution

ISRO Scientist or Engineer Electrical 2017 - Question 30

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The dielectric strength of SF6 gas (used in circuit breakers) is approximately

A

Same as that of air

B

2 to 3 times more than air

C

10 to 20 times more than air

D

2 to 3 times less than air

View Solution

ISRO Scientist or Engineer Electrical 2017 - Question 31

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Ferranti effect states that under certain conditions, the sending end voltage is

A

Less than receiving end voltage

B

Greater than receiving end voltage

C

Equal to receiving end voltage

D

Not having any impact on the receiving end voltage

View Solution

ISRO Scientist or Engineer Electrical 2017 - Question 32

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The equal area criterion of stability is applicable to

A

Two machine system and infinite bus bars

B

One machine system and infinite bus bars

C

Multi-machine system only

D

None of the above

View Solution

ISRO Scientist or Engineer Electrical 2017 - Question 33

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The power transmission capacity of the transmission line is

A

Inversely proportional to the square of the voltage

B

Proportional to the voltage

C

Inversely proportional to the voltage

D

Proportional to the square of the operating voltage

View Solution

ISRO Scientist or Engineer Electrical 2017 - Question 34

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If the torque angle ‘delta’ increases indefinitely, the system indicates

A

Steady state stability

B

Permanent stability

C

Instability

D

None of the above

View Solution

ISRO Scientist or Engineer Electrical 2017 - Question 35

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Resistance switching is normally employed in

A

All breakers

B

Bulk oil breaker

C

Minimum oil breaker

D

Air-blast circuit breaker

View Solution

ISRO Scientist or Engineer Electrical 2017 - Question 36

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Series capacitors are used to

A

Improve line frequency and eliminate harmonics

B

Compensate for line inductive reactance

C

Neutralise line capacitive reactance

D

None of the above

View Solution

ISRO Scientist or Engineer Electrical 2017 - Question 37

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Over fluxing protection is normally recommended for

A

Generator transformers in power stations

B

Auto-transformers in power stations

C

Station transformers in power stations

D

Distribution transformers

View Solution

ISRO Scientist or Engineer Electrical 2017 - Question 38

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In general AC distribution systems, arc interruption in vacuum circuit breakers are designed to function in a time period of

A

One cycle

B

Two to three cycles

C

Within ten cycles

D

None of the above

View Solution

ISRO Scientist or Engineer Electrical 2017 - Question 39

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Systems for Protection from negative sequence current is provided normally for

A

Transformers

B

Generators

C

Transmission lines

D

Motors

View Solution

ISRO Scientist or Engineer Electrical 2017 - Question 40

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Bundled conductors are mainly used in high voltage overhead transmission lines to

A

Reduce line loss

B

Reduce harmonics

C

Reduce corona

D

Increase strength

View Solution

ISRO Scientist or Engineer Electrical 2017 - Question 41

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Surge impedance of overhead transmission line is normally in the order of

A

1 - 5 ohms

B

20 - 30 ohms

C

300 - 500 ohms

D

300000 - 500000 ohms

View Solution

ISRO Scientist or Engineer Electrical 2017 - Question 42

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The bode diagram approach is applied to

A

Non-minimum phase network

B

Minimum phase network

C

Any network of a control system

D

None of the above

View Solution

ISRO Scientist or Engineer Electrical 2017 - Question 43

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Which of the following methods is the strongest tool to determine the stability and the transient response of the system?

A

Routh-Hurwitz criterion

B

Bode plot

C

Nyquist plot

D

Root locus

View Solution

ISRO Scientist or Engineer Electrical 2017 - Question 44

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If the gain of a critically damped system is increased, it will become

A

Under damped system

B

Over damped system

C

Oscillatory system

D

Critically damped system

View Solution

ISRO Scientist or Engineer Electrical 2017 - Question 45

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The frequency domain and time domain are related through

A

Laplace transform

B

Gauss elimination

C

Both (a) and (b)

D

None of the above

View Solution

ISRO Scientist or Engineer Electrical 2017 - Question 46

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A system with characteristic equation $$s^2 + 2 s^3 + 11 s^2 + 18 s + 18 = 0$$ will have closed loop poles such that

A

All poles lie in the left half of the s-plane

B

All poles lie in the right half of the s-plane

C

Two poles lie symmetrically on the imaginary axis of the s-plane.

D

No pole lies on the imaginary axis of the s-plane.

View Solution

ISRO Scientist or Engineer Electrical 2017 - Question 47

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If the gain of an open loop system is doubled, the gain margin

A

Is not affected

B

Gets double

C

Becomes half

D

Becomes one-fourth

View Solution

ISRO Scientist or Engineer Electrical 2017 - Question 48

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An all pass network imparts only

A

Negative phase to the input

B

Positive phase to the input

C

+/-90 degree phase shift to the input

D

+/-180 degree phase shift to the input

View Solution

ISRO Scientist or Engineer Electrical 2017 - Question 49

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An ON-OFF controller is

A

P controller

B

Integral controller

C

Non-linear controller

D

PID controller

View Solution

ISRO Scientist or Engineer Electrical 2017 - Question 50

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The transfer function of a phase lead controller is $$(1 + 3Ts) / (1 + Ts)$$. The maximum value of phase provided by this controller is

A

90

B

60

C

45

D

30

View Solution

ISRO Scientist or Engineer Electrical 2017 - Question 51

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The thermal time constant is the time

A

To reach the final steady temperature if the initial rate of increase of temperature were maintained constant

B

To reach 63% of final steady temperature

C

To reach 66.66% of final steady temperature

D

To reach half of the final steady temperature

View Solution

ISRO Scientist or Engineer Electrical 2017 - Question 52

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Which of the following circuit will have no transients?

A

Pure resistive circuit

B

L-C Circuit

C

R-L-C Circuit

D

R-L Circuit

View Solution

ISRO Scientist or Engineer Electrical 2017 - Question 53

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A conductor of length 100 cm moves right angles to a magnetic field of flux density of 2 wb/sq.m. with the velocity of 25 m/second. The induced emf in the conductor will be

A

25 volts

B

50 volts

C

75 volts

D

100 volts

View Solution

ISRO Scientist or Engineer Electrical 2017 - Question 54

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Which of the following devices are required to measure three phase balanced power?

A

One watt meter

B

One watt meter and one voltage transformer of 1 : 1 ratio

C

One watt meter and two voltmeters

D

None of the above

View Solution

ISRO Scientist or Engineer Electrical 2017 - Question 55

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The sensitivity of an instrument is

A

The smallest increment in the input that can be detected with certainty

B

The largest input change to which the instrument fails to respond

C

Ratio of the change in the magnitude of the output to the corresponding change in the magnitude of the input

D

Closeness of the output values for repeated application of a constant input

View Solution

ISRO Scientist or Engineer Electrical 2017 - Question 56

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Potentiometer sensitivity can be increased by

A

Decreasing current in the potentiometer wire

B

Increasing the length of the potentiometer wire

C

Decreasing the length of the potentiometer wire

D

Replacing the cell by a regulated power supply

View Solution

ISRO Scientist or Engineer Electrical 2017 - Question 57

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Low resistance is measured with

A

De Sauty’s bridge

B

Maxwell’s bridge

C

Kelvin’s double bridge

D

Wien bridge

View Solution

ISRO Scientist or Engineer Electrical 2017 - Question 58

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Which bridge is used to determine frequency?

A

Anderson bridge

B

De Sautys bridge

C

Wien bridge

D

Campell’s bridge

View Solution

ISRO Scientist or Engineer Electrical 2017 - Question 59

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The core of a moving iron instrument is made up of permalloy to

A

Increase sensitivity

B

Reduce temperature effect

C

Reduce effect of stray magnetic field

D

Reduce the size of the instrument

View Solution

ISRO Scientist or Engineer Electrical 2017 - Question 60

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Accuracy is defined as

A

The measure of consistency of the readings

B

Closeness with which an instrument reading approaches the true value of the quantity being measured

C

The smallest measurable input change

D

The ratio of the input to output

View Solution

ISRO Scientist or Engineer Electrical 2017 - Question 61

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If three amplifiers having the same bandwidth are cascaded, the bandwidth of the resulting amplifier will be

A

Better than that of each stage

B

Worse than that of each stage

C

Same as that of each stage

D

None of the above

View Solution

ISRO Scientist or Engineer Electrical 2017 - Question 62

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An element is said to have negative resistance when

A

The element has negative temperature coefficient

B

The current / voltage curve has negative slope

C

The element has negative specific resistance

D

The current / voltage curve has a positive slope

View Solution

ISRO Scientist or Engineer Electrical 2017 - Question 63

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The operational amplifiers are seldom used for differentiation because

A

Of the problem of drift with differentiating circuits

B

Because of the poor efficiency

C

Because of the complex circuitry requirements

D

The noises are amplified and this can be significant in the output.

View Solution

ISRO Scientist or Engineer Electrical 2017 - Question 64

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Which of the following multivibrator is called the flip flop?

A

Astable multivibrator

B

Monostable multivibrator

C

Bistable multivibrator

D

Both (b) and (c)

View Solution

ISRO Scientist or Engineer Electrical 2017 - Question 65

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The amount of feedback applied to an amplifier reduces the gain by a factor of 10. The bandwidth

A

Decreases by factor of 10

B

Increases by a factor of 10

C

Remains the same

D

None of the above

View Solution

ISRO Scientist or Engineer Electrical 2017 - Question 66

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In a negative feedback amplifier, the output impedance is decreased

A

If the signal sampled is a voltage

B

If the signal sampled is a current

C

If the feedback signal is a voltage

D

If the feedback signal is a current

View Solution

ISRO Scientist or Engineer Electrical 2017 - Question 67

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The ROM consists of

A

A decoder followed by an encoder

B

An encoder followed by a decoder

C

A multiplexer followed by a decoder

D

A multivibrator

View Solution

ISRO Scientist or Engineer Electrical 2017 - Question 68

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An ideal rectifier should have transformer utilization factor (TUF) of 1. If the actual TUF is 3.5, it shows that

A

Diode is under-loaded

B

The transformer must be 3.5 times larger

C

The transformer should be only 1/3.5 times the ideal size

D

The ripple factor is low

View Solution

ISRO Scientist or Engineer Electrical 2017 - Question 69

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A power MOSFET is a

A

Voltage controlled device

B

Current controlled device

C

Frequency controlled device

D

None of the above

View Solution

ISRO Scientist or Engineer Electrical 2017 - Question 70

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When transistors are used in series or parallel, a snubber circuit is used to

A

Control the current

B

Control the voltage

C

Limit di/dt

D

All of these

View Solution

ISRO Scientist or Engineer Electrical 2017 - Question 71

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$$\lim_{x \rightarrow \infty}\left(\frac{x + \sin x}{x}\right)$$ is equal to

A

$$-\infty$$

B

$$0$$

C

$$1$$

D

$$\infty$$

View Solution

ISRO Scientist or Engineer Electrical 2017 - Question 72

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A fair (unbiased) coin was tossed four times in succession and resulted in the following outcomes: (i) Head (ii) Head (iii) Head (iv) Head. The probability of getting a ‘Tail’
when the coin is tossed again is

A

0

B

$$\frac{1}{2}$$

C

$$\frac{4}{5}$$

D

$$\frac{1}{5}$$

View Solution

ISRO Scientist or Engineer Electrical 2017 - Question 73

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What are the eigen values of the following $$2 \times 2$$ matrix $$\begin{bmatrix}2 & -1 \\-4 & 5 \end{bmatrix}$$ ?

A

-1 and 1

B

1 and 6

C

2 and 5

D

4 and -1

View Solution

ISRO Scientist or Engineer Electrical 2017 - Question 74

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$$\int_{0}^{\frac{\pi}{2}} \int_{0}^{\frac{\pi}{2}} \sin (x + y)dx dy $$ is

A

0

B

$$\pi$$

C

$$\frac{\pi}{2}$$

D

2

View Solution

ISRO Scientist or Engineer Electrical 2017 - Question 75

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In the Taylor series expansion of $$e^x + \sin x$$ about the point $$x = \pi$$ , the coefficient

A

$$e^{\pi}$$

B

$$0.5 e^{\pi}$$

C

$$e^{\pi + 1}$$

D

$$e^{\pi - 1}$$

View Solution

ISRO Scientist or Engineer Electrical 2017 - Question 76

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A deck of five cards (each carrying a distinct number from 1 to 5) is shuffled thoroughly. Two cards are then removed from the deck, one at a time. What is the probability that the two cards are selected with the number of the first card being one higher than the number on the second card?

A

$$\frac{1}{5}$$

B

$$\frac{4}{25}$$

C

$$\frac{1}{4}$$

D

$$\frac{2}{5}$$

View Solution

ISRO Scientist or Engineer Electrical 2017 - Question 77

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Using trapezoidal rule for the table given below $$\int_{4}^{5.2} \ln x dx$$ will be

A

1.8277

B

1.9284

C

1.6424

D

0.98795

View Solution

ISRO Scientist or Engineer Electrical 2017 - Question 78

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Find the z transform of $$(n + 1)^2$$

A

$$\frac{z^2(2z + 1)}{(z - 1)^3}$$

B

$$\frac{(2z + 1)}{(z - 1)^3}$$

C

$$\frac{(2 + z)}{(z - 1)^2}$$

D

$$\frac{(3z + 2)}{z - 1}$$

View Solution

ISRO Scientist or Engineer Electrical 2017 - Question 79

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Consider the following system of equations in three real variables $$x_1, x_2$$ and $$x_3$$
$$2x_1 - x_2 + 3x_3 = 1$$
$$3x_1 - 2x_2 + 5x_3 = 2$$
$$-x_1 - 4x_2 + x_3 = 3$$
The system of equations has :

A

No solutions

B

A unique solution

C

More than one but a finite number of solutions

D

An infinite number of solutions

View Solution

ISRO Scientist or Engineer Electrical 2017 - Question 80

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Which of the following functions would have only odd powers of x in its Taylor series expansion about the point x = 0?

A

$$\sin(x^3)$$

B

$$\sin(x^2)$$

C

$$\cos(x^3)$$

D

$$\cos(x^2)$$

View Solution