ISRO Scientist or Engineer Electrical 2013

ISRO Scientist or Engineer Electrical 2013 - Question 1

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The energy stored in the magnetic field in a solenoid of length 30cm and diameter 3 cm wound with 1000 turns of wire & carrying a current of 10A is

A

0.015 joules.

B

0.15 joules.

C

0.5 joules.

D

1.15 joules

View Solution

ISRO Scientist or Engineer Electrical 2013 - Question 2

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A network is said to be linear, if and only if

A

The response is proportional to the excitation function.

B

The principle of superposition applies.

C

The principle of homogeneity applies.

D

The principles of superposition and homogeneity apply.

View Solution

ISRO Scientist or Engineer Electrical 2013 - Question 3

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Kirchoff's law fails in the case of

A

Non-linear networks.

B

Linear networks.

C

Dual networks.

D

Distributed parameter networks

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ISRO Scientist or Engineer Electrical 2013 - Question 4

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In a four branch parallel circuit, 50mA current flows in each branch. If one of the branches opens, the current in other branches

A

Increase, but not double.

B

Decrease.

C

Unaffected.

D

Double.

View Solution

ISRO Scientist or Engineer Electrical 2013 - Question 5

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The wave length of a wave in a waveguide is

A

is greater than in free space

B

depends only on the waveguide dimensions and the free-space wavelength

C

is inversely proportional to the phase velocity

D

is directly proportional to the group velocity

View Solution

ISRO Scientist or Engineer Electrical 2013 - Question 6

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Characteristic impedance of a quarter wave transformer connected in between a load of 100 ohm and a transmission line of characteristic impedance 225 ohms is

A

100 ohm

B

225 ohm

C

600 ohm

D

150 ohm

View Solution

ISRO Scientist or Engineer Electrical 2013 - Question 7

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A transverse electromagnetic wave with circular polarization is received by a dipole antenna due to polarization mismatch. The power transfer efficiency from the waveto the antenna is reduced to about

A

50%

B

35.5%

C

25%

D

0%

View Solution

ISRO Scientist or Engineer Electrical 2013 - Question 8

Report

The unit of displacement density of a magnetic circuit is

A

Coulomb / metre

B

Coulomb / sq. metre

C

Newton - cm

D

Amp / metre

View Solution

ISRO Scientist or Engineer Electrical 2013 - Question 9

Report

The derivative of an ideal step function is

A

an impulse function

B

zero

C

sine function

D

undefined

View Solution

ISRO Scientist or Engineer Electrical 2013 - Question 10

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An impulse function consists of

A

entire frequency range with same relative phase

B

infinite bandwidth with linear phase variation

C

pure DC

D

large DC with weak harmonics

View Solution

ISRO Scientist or Engineer Electrical 2013 - Question 11

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The discrete time system described by $$y(n) = x(n^2)$$ is

A

causal, linear and time varying

B

causal, nonlinear and time varying

C

non-causal, linear and time invariant

D

non-causal, non linear and time variant

View Solution

ISRO Scientist or Engineer Electrical 2013 - Question 12

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What doesthe transfer function of a system describe for the system?

A

only zero input response

B

only zero state response

C

both zero input and zero state response

D

neither zero input response nor zero state response

View Solution

ISRO Scientist or Engineer Electrical 2013 - Question 13

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Which of the following measures cannot be effective in reducing the noise?

A

reduction in signaling rate

B

increase in transmitted power

C

increase in channel bandwidth

D

use of redundancy

View Solution

ISRO Scientist or Engineer Electrical 2013 - Question 14

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Which among the following type of transformer have smallest size with same electrical specification ?

A

ONAN type transformer.

B

Dry type transformer.

C

ONAF type transformer.

D

OFWF type transformer.

View Solution

ISRO Scientist or Engineer Electrical 2013 - Question 15

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Two transformers operating in parallel will share the load depending upon their ?

A

Ratings.

B

Leakage reactance.

C

Efficiency.

D

Per unit impendence.

View Solution

ISRO Scientist or Engineer Electrical 2013 - Question 16

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Transformer core is laminated,

A

because it is difficult to fabricate solid core.

B

because laminated core provides high flux density.

C

to avoid eddy current and hysteresis losses.

D

to increase the main flux.

View Solution

ISRO Scientist or Engineer Electrical 2013 - Question 17

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The eddy current lossesin the transformer will be reduced if ?

A

The laminations are thick.

B

Number ofturns in the primary winding is reduced.

C

The numberof turns in the secondary winding is reduced.

D

The laminations are thin.

View Solution

ISRO Scientist or Engineer Electrical 2013 - Question 18

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The Buchholz relay is used to protect the ?

A

Alternators againstall 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 2013 - Question 19

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Why are transformer stamping annealed before being used for the building?

A

to reduce eddy-current loss due to burning of edges

B

to reduce hysteresis loss due to burning of edges

C

to give mechanical strength to the core

D

to increase core permeability

View Solution

ISRO Scientist or Engineer Electrical 2013 - Question 20

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As compared to $$\triangle$$ — $$\triangle$$ bank, the capacity of the V — V bank of transformers is ---- percent.

A

57.7

B

66.7

C

50

D

86.6

View Solution

ISRO Scientist or Engineer Electrical 2013 - Question 21

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

A

which is the same as the steady-state magnetizing current

B

which is several times the steady-state magnetizing current, depending upon the initial state of the residual flux in the transformer core.

C

which is several times the steady-state magnetizing current, independent of the initial state of the residual flux in the transformer core.

D

which is twice the steady-state magnetizing current provided the core has no residual flux.

View Solution

ISRO Scientist or Engineer Electrical 2013 - Question 22

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On the twosidesof a star/delta transformer ----

A

the voltage and current are both in phase

B

the voltage and current both differ in phase by $$30^\circ$$

C

the voltage differ in phase by $$30^\circ$$ but currents are in phase

D

the current differ in phase by $$30^\circ$$ butvoltages are in phase.

View Solution

ISRO Scientist or Engineer Electrical 2013 - Question 23

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In a Scott-connected transformer the number of primary and teaser turns respectively are ----

A

$$N, \frac{2}{\surd{3} N}$$

B

$$\frac{N}{2}, N$$

C

$$\frac{\surd{3} N}{2}, N$$

D

$$N, \frac{\surd{3} N}{2}$$

View Solution

ISRO Scientist or Engineer Electrical 2013 - Question 24

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The use of higher flux density in the transformer design ---

A

decreases the total weight / kVA

B

increases the total weight / kVA

C

decreases the weightof iron / kVA but increasesthat of copper

D

decreases the weight of copper / kVA but increases that of iron

View Solution

ISRO Scientist or Engineer Electrical 2013 - Question 25

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The applied voltage of a certain transformer is increased by 50% while the frequency is reduced by 50%. The maximum coreflux density will become ---

A

three times

B

1.5 times

C

0.5 times

D

will remain the same

View Solution

ISRO Scientist or Engineer Electrical 2013 - Question 26

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

A

Copper loss

B

Hysterisis loss

C

Core loss

D

Eddy current loss.

View Solution

ISRO Scientist or Engineer Electrical 2013 - Question 27

Report

Distribution transformers have core loss

A

More than full load copper loss

B

Equal to full load copper loss

C

Less than full load copper loss

D

Negligible compared to full load copper loss

View Solution

ISRO Scientist or Engineer Electrical 2013 - Question 28

Report

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

A

SC test.

B

OC test.

C

Half time on SC and half time on OC.

D

Sumpner’s test.

View Solution

ISRO Scientist or Engineer Electrical 2013 - Question 29

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In power lines, series capacitors are used to----

A

Improve line frequency.

B

Compensate inductive reactance.

C

Compensate capacitive reactance

D

Balance harmonics.

View Solution

ISRO Scientist or Engineer Electrical 2013 - Question 30

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The starting torque of a slip ring induction motor can be increased by

A

Adding external resistance to rotor

B

Adding external inductance to rotor

C

Adding external capacitance to rotor

D

Adding external RLC circuit to rotor

View Solution

ISRO Scientist or Engineer Electrical 2013 - Question 31

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The synchronous speedof a four-pole induction motor operating at 50Hz is

A

25rps

B

1560 rpm

C

3000 rpm

D

1000 rpm

View Solution

ISRO Scientist or Engineer Electrical 2013 - Question 32

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A shunt generator has a critical field resistance of 200 ohm at a speed of 800r.p.m. If the speed of the generator is increased to 1000r.p.m., what is the change in critical field resistance of the generator?

A

Decrease to 160 ohm

B

Remains the same at 200 ohm

C

Increases to 250 ohm

D

Increases to 312.5 ohm

View Solution

ISRO Scientist or Engineer Electrical 2013 - Question 33

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A three-phase slip ring induction motor is fed from the rotor side with stator winding short circuited. The frequency of currents flowing in short circuited stator is

A

Slip frequency

B

Supply frequency

C

Frequency corresponding to rotor speed

D

Zero

View Solution

ISRO Scientist or Engineer Electrical 2013 - Question 34

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When the supply voltage to an induction motoris reduced by 10%, the maximum torque decreased by approximately

A

5%

B

10%

C

20%

D

40%

View Solution

ISRO Scientist or Engineer Electrical 2013 - Question 35

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A 3-phase induction motor is driving full-load torque which is independent of speed. If line voltage drops to 90% of the rated value, percentage increase in motor copper losses

A

23%

B

-18%

C

123%

D

25%

View Solution

ISRO Scientist or Engineer Electrical 2013 - Question 36

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The injected e.m.f in the rotor of an induction motoris of

A

The same frequencyas slip frequency

B

The same phase as the rotor e.m.f

C

A high value for satisfactory speed control

D

The same phase as rotor e.m.f and a high value for satisfactory speed control.

View Solution

ISRO Scientist or Engineer Electrical 2013 - Question 37

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If the full-load speed of a 3-phase, 50Hz induction motor is 950 r.p.m, what is its half load speed nearly equal to?

A

100 r.p.m

B

450 r.p.m

C

1900 r.p.m

D

975 r.p.m

View Solution

ISRO Scientist or Engineer Electrical 2013 - Question 38

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For controlling the speed of an induction motor the frequency of supply is increased by 10%. For magnetizing current to remain the same, the supply voltage must

A

Be reduced by 10%

B

Remain constant

C

Be increased by 10%

D

Be reducedor increased by 20%

View Solution

ISRO Scientist or Engineer Electrical 2013 - Question 39

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The speed of an induction motoris controlled by varying the supply frequency keeping V/f constant, then

A

Breakdown torque and magnetizing current would both remain constant

B

Breakdown torque would remain constant but magnetizing current would increase.

C

Breakdown torque would decrease but magnetizing current would remain constant.

D

Breakdown torque and magnetizing current both would decrease.

View Solution

ISRO Scientist or Engineer Electrical 2013 - Question 40

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A synchronous generator connected to an infinite bus is overexcited. Consider the only reactive power, from the point of view of the system, the machine acts as

A

a capacitor

B

an inductor

C

a resistor

D

none of these

View Solution

ISRO Scientist or Engineer Electrical 2013 - Question 41

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The voltage stress will be maximum in an underground cable at

A

The surface of the sheath

B

The surface of the conductor

C

The surface o the insulation.

D

The surface of the armour.

View Solution

ISRO Scientist or Engineer Electrical 2013 - Question 42

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The dielectric strength of air at a barometric pressure of 76cm and 25 degree centigrade is

A

30 kv/ metre.

B

21.1 kv rms /cm.

C

21.1 kv rms / mm.

D

110 kv / metre.

View Solution

ISRO Scientist or Engineer Electrical 2013 - Question 43

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The positive sequence current of a transmission line is

A

always zero

B

one-third of negative sequence current

C

three times the negative sequence current

D

equal to negative sequence current

View Solution

ISRO Scientist or Engineer Electrical 2013 - Question 44

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For the fault at the terminals of a synchronous generator, the fault current is maximum for a

A

3-phase fault

B

3-phase to ground fault

C

Line-to-ground fault

D

Line-to-line fault

View Solution

ISRO Scientist or Engineer Electrical 2013 - Question 45

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The earth transformer is used to

A

Avoid the harmonics in the transformers

B

Provide artificial neutral earthing where neutral point is not accessible

C

Improve stability of the system

D

Measure the voltage

View Solution

ISRO Scientist or Engineer Electrical 2013 - Question 46

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For differential protection of power transformer (delta-delta) the current transformers will have

A

Delta-delta connection

B

Star-delta connection

C

Star-star connection

D

Delta-star connection

View Solution

ISRO Scientist or Engineer Electrical 2013 - Question 47

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For the protection of a very long extra high voltage line, the protective relay used is

A

Over current with extremely inverse characteristics

B

Percentage differential relay

C

Reactance type distance relay

D

Mho type distance relay

View Solution

ISRO Scientist or Engineer Electrical 2013 - Question 48

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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 2013 - Question 49

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Symmetrical breaking capacity of ACB is

A

Greater than asymmetrical breaking capacity

B

Less than asymmetrical breaking capacity

C

Equal to asymmetrical breaking capacity

D

not related to asymmetrical breaking capacity

View Solution

ISRO Scientist or Engineer Electrical 2013 - Question 50

Report

By which material the fuse element is generally made

A

Copper

B

Nickel

C

Iron alloy

D

Silver

View Solution

ISRO Scientist or Engineer Electrical 2013 - Question 51

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Grounding is generally done in transmission line at

A

The supply end

B

The receiving end

C

Middle of the line

D

Anywhere

View Solution

ISRO Scientist or Engineer Electrical 2013 - Question 52

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What is the approximate value of the surge impedance loading of a 400 kV, 3-phase 50Hz overhead single circuit transmission line

A

230 MW

B

400 MW

C

1000 MW

D

1600 MW

View Solution

ISRO Scientist or Engineer Electrical 2013 - Question 53

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When two identical first order systems have been cascaded non - interactively the unit step response of the system will be

A

Over damped

B

Under damped

C

Un-damped

D

Critically damped

View Solution

ISRO Scientist or Engineer Electrical 2013 - Question 54

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Which of the following methods is most strong 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 2013 - Question 55

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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 2013 - Question 56

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Phase margin of a system is used to specify

A

Relative stability

B

Absolute stability

C

Time response

D

Frequency response

View Solution

ISRO Scientist or Engineer Electrical 2013 - Question 57

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The rms value of an alternating current is given by steady DC current which when flowing through a given circuit fora given time produces,

A

The same heat as produced by AC when flowing through the same circuit.

B

The less heat than produced by AC when flowing through the same circuit.

C

The more heat than produced by AC when flowing through the same circuit.

D

14.4 calories.

View Solution

ISRO Scientist or Engineer Electrical 2013 - Question 58

Report

AC current cannot be measured directly by

A

Hot wire ammeter

B

Moving iron ammeter

C

Moving coil ammeter

D

Thermocouple type ammeter

View Solution

ISRO Scientist or Engineer Electrical 2013 - Question 59

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The internal resistance of a voltmeter should be very high in order to have

A

High voltage range

B

Maximum current through the meter

C

Minimum current through the meter

D

More current from the voltage source

View Solution

ISRO Scientist or Engineer Electrical 2013 - Question 60

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The resistance of a thermistor

A

Increases with the increase of temperature

B

Decreases with the increase of temperature

C

Remains constant with the increase of temperature

D

Remains constant with the decrease of temperature

View Solution

ISRO Scientist or Engineer Electrical 2013 - Question 61

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The early effect in a bipolar junction transistor is caused by

A

Fast turn on

B

Fast turn off

C

Large collector-base reverse bias

D

Large emitter-base reverse bias

View Solution

ISRO Scientist or Engineer Electrical 2013 - Question 62

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Fermi level for an n-type semiconductor lies

A

Near valence band

B

Near conduction band

C

In valence band

D

In conduction band

View Solution

ISRO Scientist or Engineer Electrical 2013 - Question 63

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For a forward biased pn-junction diode diffusion capacitance varies

A

Linearly with current

B

Square of current

C

Inversely with Current

D

Does not vary with current

View Solution

ISRO Scientist or Engineer Electrical 2013 - Question 64

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In a multi-stage R-C coupled amplifier, the coupling capacitor

A

Limits the low frequency response

B

Limits the high frequency response

C

Does not affect the frequency response

D

Block the d.c. component without affecting the frequency response

View Solution

ISRO Scientist or Engineer Electrical 2013 - Question 65

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An operation amplifier should preferably have

A

Low out put impedance

B

High out put impedance

C

Infinite impedance

D

Impedance is insignificant

View Solution

ISRO Scientist or Engineer Electrical 2013 - Question 66

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The output voltage of an operational amplifieris ?

A

90 degree out of phase from the input.

B

180 degree out of phase from the input.

C

45 degree out of phase from the input.

D

-90 degree out of phase from the input.

View Solution

ISRO Scientist or Engineer Electrical 2013 - Question 67

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A class-A transformer coupled, transistor power amplifier is required to deliver a power output of 10 Watts. The maximum power rating of the transistor should be less than

A

5 W

B

10 W

C

20 W

D

40 W

View Solution

ISRO Scientist or Engineer Electrical 2013 - Question 68

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Which of the following Boolean algebra rules is correct?

A

$$A.\overline{A} = 1$$

B

$$A + AB = A + B$$

C

$$A + \overline{A}B = A + B$$

D

$$A(A + B) = B)$$

View Solution

ISRO Scientist or Engineer Electrical 2013 - Question 69

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In an all NOR gate realization of a combinational circuit all EVEN and ODD level gates behave like

A

OR and AND

B

AND and OR

C

OR and NOT

D

NOR and AND

View Solution

ISRO Scientist or Engineer Electrical 2013 - Question 70

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Use of a reverse conducting thyristor in place of antiparallel combination of thyristor and feedback diode in an inverter:

A

Effectively minimizes the peak commutating current

B

Decreases the operating frequency of operation

C

Minimizes the effects of load inductance on the commutation performance

D

Causes deterioration in the commutation performance

View Solution

ISRO Scientist or Engineer Electrical 2013 - Question 71

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In a resonance pulse inverter:

A

DC output voltage variation is wide

B

The frequency is low

C

The output voltage is never sinusoidal

D

DC saturation of transformer core is minimized

View Solution

ISRO Scientist or Engineer Electrical 2013 - Question 72

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The vectors $$x_1 = (1, 2, 4), x_2 = (2, -1, 3), x_3 = (0, 1, 2), x_4 = (-3, 7, 2)$$ are

A

Linearly independent

B

Linearly dependent

C

No relation

D

Exponentially dependent

View Solution

ISRO Scientist or Engineer Electrical 2013 - Question 73

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Characteristic roots of matrix $$A$$ and $$A^T$$ will be

A

Different

B

Same

C

Cannot say about roots

D

None of these

View Solution

ISRO Scientist or Engineer Electrical 2013 - Question 74

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The minimum point of the function $$\left(\frac{x^3}{3}\right) - x$$ is at

A

$$x = 1$$

B

$$x = -1$$

C

$$x = 0$$

D

$$x = \frac{1}{\surd{3}}$$

View Solution

ISRO Scientist or Engineer Electrical 2013 - Question 75

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The area bounded by the curves $$y^2 = 9x, x - y + 2 = 0$$ is given by

A

1

B

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

C

$$\frac{3}{2}$$

D

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

View Solution

ISRO Scientist or Engineer Electrical 2013 - Question 76

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The integrating factor of equation $$\sec^2 y \frac{dy}{dx} + x \tan y = x^3$$ is

A

$$[e]^{\frac{x^2}{2}}$$

B

$$[e]^{\frac{-x^2}{2}}$$

C

$$[e]^{\frac{x}{2}}$$

D

$$[e]^{\frac{-x}{2}}$$

View Solution

ISRO Scientist or Engineer Electrical 2013 - Question 77

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An urn contains 5 black and 5 white balls. The probability of drawing two balls of the same colour

A

$$\frac{2}{9}$$

B

$$\frac{4}{9}$$

C

$$\frac{1}{9}$$

D

$$\frac{5}{9}$$

View Solution

ISRO Scientist or Engineer Electrical 2013 - Question 78

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Ten percent of screws produced in a certain factory turn out to be defective. Find the probability that in a sample of 10 screws chosen at random, exactly two will be defective.

A

0.2

B

0.25

C

0.8

D

0.3

View Solution

ISRO Scientist or Engineer Electrical 2013 - Question 79

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The Equation $$x^3 - x^2 + 4x - 4 = 0$$ is is to be solved using the Newton-Raphson method. If $$x = 2$$ is taken as the initial approximation of the solution, then the next approximation using the method will be

A

$$\frac{2}{3}$$

B

$$\frac{4}{3}$$

C

$$\frac{1}{3}$$

D

$$\frac{5}{3}$$

View Solution

ISRO Scientist or Engineer Electrical 2013 - Question 80

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The unique polynomial P(x) of degree 2 such that: P(1) = 1, P(3) = 27, P(4) = 64 is

A

$$8x^2 - 19x + 12$$

B

$$8x^2 + 19x + 12$$

C

$$-8x^2 - 19x + 12$$

D

$$-8x^2 - 19x - 12$$

View Solution