electronics let exam.2008.doc

7/27/2019 electronics let exam.2008.doc

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ELECTRONICS AND COMMUNICATIONS

TIME: 2hrs MAX;MARKS: 120

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1) The requirement of an oscillator using positive feedback amplifier as, is that

a) there must be positive feedback

b) initially the value of loop gain A must be greater than unity

c) after the desired level is reached the loop gain A must be decreased to unity

d) none of the above

2) In RC feedback oscillator the frequency depends on the values of

a) R

b) C

c) R and C

d) none of these

3) An oscillator using LC tuned circuit has L = 58.6H and C = 300pF. The frequency of

oscillations will be nearly

a)

b) 12KHz

c) 120 KHz

d) 1200 KHz

e) 12000 KHz

4) Positive feedback is the same as

a) Frequency synthesis

b) negative feedback

c) degeneration

d) regeneration

5) Which of the following is the most stable oscillator?

a) Wein bridge oscillator

b) Hartley oscillator

c) Colpitts oscillator

d) Crystal Controlled oscillator

6) A junction FET can operate in

a) depletion mode only

b) enhancement mode onlyc) Depletion and enhancement modes


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d) Neither depletion nor enhancement modes.

7) When n channel depletion type MOSFET are used in enhanced mode,

a) the gate will be +ve

b) the gate will be ve

c) the gate will be at ground level

d) none of these

8) The overall gain of multistage amplifier in dB is equal toa) the sum of all individual amplifier stage gains

b) product of all individual amplifier stage gains

c) both (a) & (b) d) none of these

9) A class A amplifier is that one in which

a) base is biased to cut off

b) Ic flows most of the time

c) Ie flows all the time

d) none of these

10) A complimentary symmetry amplifier has

a) 1 PNP and 1 NPN transistor

b) 2 PNP transistors

c) 2NPN transistors

d) 2 P channel FET

11) The gain of the amplifier with negative feed back is

a) Increased by

b) Decreased by

c) Increased by

d) Decreased by

12) Which of the following types of amplifier can corresponds to a half wave rectifier (for

voltage wave form

a) class A amplifier

b) class B amplifier

c) class C amplifier

d) class D amplifier

13) Then minimum gate voltage to operate a MOSFET is the

a) threshold voltage

b) pinch off voltage

c) saturation voltage


14) The process of converting ac to dc is called

a) amplification

b) rectification

c) modulation

d) alternation

15) The ripple frequency of a full wave rectifier is

a) Twice the supply frequency

b) Equal to supply frequency

c) Thrice the supply frequency

d) None of these

16) The peak inverse voltage (PIV) of half wave rectifier is


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a) Em b) 2Em c) 3Em d) 4Em

17) The disadvantage of bridge rectifier is that

a) it is costly

b) it used 4 diodes

c) it has high PIV

d) both (a) & (c)

18) The relation of a transistor current is

a) Ic = Ie + Ib

b) Ie = Ic + Ib

c) Ib = Ic + Ie

d) Ic = Ie x Ib

19) In CB transistor amplifier, the phase difference between output voltage and input voltage

is

a) Zero b) 180 c) 90 d) 45

20) A pn junction diode cannot be used for

a) Rectification

b) Amplification

c) obtaining light radiation

d) detecting light intensity

21) The depletion region of PN junction is one, that is depleted of

a)

b) Atoms

c) mobile charges

d) immobile charges

e) none

22) For Silicon, the energy gap at 300k is

a) 1.1 watt

b) 1.1 eV

c) 1.1 J

d) 0.72 eV

23) When forward bias is applied to a junction diode, it

a) increases the potential barrier

b) decreases the potential barrier

c) reduces the majority carrier current to zero

d) reduces the minority carrier current to zero


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24) The donor type impurity is

a) Phosphorous

b) Aluminium

c) Boron

d) Iron

25) Which of the following is an active component

a) Semiconductor devices

b) Resistors

c) Capacitors

d) inductors

26) Free electrons exist in

a) first band

b) second band

c) valence band

d) conduction band

27) In a semiconductor the forbidden energy gap is of the order of

a) 1 eV b) 5 eV c) 1 KeV d) 1 MeV

28) Holes are formed at

a) Depletion region

b) Conduction band

c) Valance band

d) Nucleu

29) The current gain of the transistor in CB mode is .995. its gain in CE mode is

a) 99.5 b) 100 c) 200 d) .995

30) What is the no: of junctions in a semiconductor diode

a) One

b) Two

c) Three

d) no junction

31) The circuit given below is functionally equivalent to

a) EXOR b) NOR


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c) Comparator d) Inhibit gate

32) Which of the following Boolean algebra statements represents distributive law

a) (A+B)+C=A(B+C)

b) A.(B+C)=AB+AC

c) A.(B.C)=(AB).C

d) AB=BA

33) Decimal equivalent of binary 1010.01 is

a) 12.25

b) 10.25

c) 10.01

d) 10.12

34) F= represents Gate

a) NAND

b) NOR

c) OR

d) EXOR

35) Excess 3 code is also

a) Weighted code

b) Cyclic redundancy code

c) Self complimenting code

d) Both a and c

36) Decimal number 85 is encoded as 1100 0101 it is in

a) 8421 b) 4421 c) 2421 d) 2221

37) The process of superimposing signal frequency on the carrier frequency is called

a) Transmission

b) Modulation

c) Detection

d) Reception

38) The max. Frequency applied to a CRO is limited by

a) Vertical amplifier

b) the horizontal amplifier


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c) the sync signal frequency

d) Coating material of the screen

39) A 1 m.A, 50 meter movement is used to make a voltmeter of range 50 v. The series

resistance to be connected is

a) 10 k

b) 49.95 k

c) 50 k

d) 499.95 k

40) Lissajous patterns obtained on a CRO can be used to determine

a) phase shift

b) voltage amplitude

c) amplitude distortion


41) To measure the current in an electric device

a) put an ammeter in parallel with it

b) put an voltmeter in parallel with it

c) put an ammeter in series with it

d) put a voltmeter in series with it

42) The resistance of an ideal volt meter is

a) Zero

b) Infinite

c) > 1 k

d) 1

43) Which one is the active transducer

a) RTD

b) Thermister

c) Thermocouple

d) LV

44)LVDT is a

a) inductive transducer

b) capacitor transducer

c) resistive transducer

d) None of the above

45) The scale of voltmeter is uniform. Its type is

a) Moving iron

b) Induction

c) Moving coil permanent magnet

d) Moving coil dynamometer

46) A digital signal processesa) continuously varying values b) only two discrete values


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c) only 4 discrete values d) none of the above

47) Modern communication systems use

a) analog circuits

b) digital circuits

c) combination of analog & digital circuitsd) none of the above

48) RADAR is the acronym for

a) Radiation and Direction Apparatus

b) Radio Detection and Ranging

c) Receiver and Detector Apparatus

d) None of these

49) The frequency deviation of an FM signal

a) increases with the frequency of modulating signal

b) decreases with the frequency of modulating signal

c) remains the same even when the frequency of modulating signal changes

d) none of these

50) Modulation index for an FM signal is

a) The ratio of max frequency deviation to the highest modulation frequency

b) the ratio of max. frequency deviation to the lowest modulation frequency

c) the ratio of min. frequency deviation to the highest modulation frequency

d) None of these

51) The maximum frequency deviation standard for FM broadcast

a) 75KHz

b) 75 Hz

c) 75 MHz

d) 50 KHz52) If in an FM signal, the maximum frequency deviation is 37.5 KHz, the modulation is

a) 100% b) 0% c) 50% d) 25%

53) When the percentage of modulation falls in AM

a) power in the carrier band falls

b) power in the carrier increase rapidly

c) power in the side band falls

d) power in the side bands increase

54) Most of the power in an AM modulated signal resides with the

a) upper side band

b) lower side band

c) carrier signal band


55) Which of the following is desirable in narrow band FM

a) Higher modulation percentage

b) Lower modulation percentage

c) zero modulation percentage

d) none of these

56) If modulation is more than 100%, the modulation is called

a) over modulation

b) percentage modulation

c) modulation index

d) none of these

57) Percentage of modulation is expressed as

a) Emax Emin / Emax + Emin) x100

b) (Emax / Emin ) x 100

c) (Emax + Emin / Emax Emin ) x100

d) (Emin / Emax ) x100


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58) If the highest modulation frequency is 5 kHz, the bandwidth isa) 5KHz

b) 2.5 KHz

c) 10 KHz

d) None of the above

59) An fm modulation signal containing the sound intelligence to a television broadcast has amaximum frequency deviation of 50 KHz. The depth of modulation is

a) 66.66%

b) 100%

c) 50%

d) None of these

60) In the spectrum of an amplitude modulated wave :

a) consists of 2 sidebands and a carrier band

b) The number of significant bands depends upon modulation index.

c) carrier frequency vanishes when modulation index is large

d) None of the above.

61) Oscillator crystal are made of

a) Silicon

b) Germanium

c) Quartz

d) None

62) 3. For small size, high frequency coils, the most common core material is-

a) Air

b) Ferrite

c) Powdered ion

d) Steel

63) If we have a parallel plate capacitor of plate area 'A' and plate separatoin t and having

a capacity C and a metallic plate r of area A and of negligible thickness is introduced in

the capacitor at a distance from either of the two plates then the capacity of the capacitor

will become

a) c/2 b) C c) 2C d) 4C

64) RF amplifier of an A.M. receiver is normally biased in

a) Class 'A' b) Class 'b' c) Class 'C' d) None

65) The value of gate voltage for the operation of enhancement of only N channel MOSFET

has to be

a) High positive

b) High negative

c) Low positive

d) Zero


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66) The input gate current of a FET is a) a few microamperes

b) negligibly small

c) a few mill amperes

d) a few amperes

67) Which one of below used D/A converter

a) PCM modulator

b) PAM modulator

c) PCM demodulator

d) PWM

68) In order to get maximum undistorted output signal from CE amplifier with VCC 10V, the

value of VCE (Q) should be approximately

a) 0.1V b) 5V c) 10V d) V

69) In a FET the electrode, which corresponds to collector in bipolar transistor, is

a) source b) drain c) gate d) none

70) The device which acts like an NPN and a PNP transistor connected base to base and

emitter to collector is

a) Triac b) UJT c) Diac d) SCR

71) The maximum power will transfer when the source connected with a load of

a) Same impedance

b) Les impedance

c) Higher impedance

d) Medium impedance

72) RC time constant indicates

a) Time taken to fully charge

b) Time taken to charge 50%

c) Time taken to charge 69%

d) Time taken to charge 80%

73) For A doplar radar duplexer used to

a) Protect radar from enemies

b) Protect receiver

c) Protect transmitter

d) Protect from mixing of transmitting and receiving signals

74) Wave guide is a

a) Soft ware b) Oscillator


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c) Hollow conductor d) Duplexer

75) Number of frame per second used in modern TV IS

a) 25 b) 50 c) 24 d) 30

76) The coding system typically used in digital telemetry is

a) PPM (pulse position modulation)

b) PAM (pulse amplitude modulation)

c) PCM (pulse code modulation)

d) PDM (pulse duration modulation)

77) The energy band of atoms are formed by

a) A single atom

b) Several atoms

c) Nucleus

d) Protons

78) The velocity of X ray is_________ in m/s

a) 2.58x1023

b) 3x 108

c) 30000

d) 258956

79) Direct coupling is used for

a) Low frequency

b) High frequency

c) Medium frequency

d) Very high frequency

80) Op amps can be used as a

a) Comparator

b) Differentiator

c) Adder

d) All of the above

81) Data in the serial form can be converted into parallel form by using

a) PISO shift register

b) SOIP shift register

c) SIPO shift register

d) POIS shift register

82) PROMs are used to store-

a) bulk information

b) information to be accessed rarely

c) sequence information


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d) relatively permanent information

83) 'Not allowed' condition in NAND gate SR flip flop is

a) s = 0, R = 0

b) s = 1, R = 1

c) s = 0, R = 1

d) s = 1, R = 0

84) Name the fastest logic family-

a) TTL b) RTL c) DCTL d) ECL

85) For the signal g (t) = 10 cos (50 t) cos2 (150t) The Nyquist sampling state in one

second is

a) 150 samples per second

b) samples per second

c) 300 samples per second

d) 350 samples per second

86) Compander is used in PCM for

a) Reduce the %error in high value

b) Reduce the %error in low value

c) For linear quantizer

d) Not used in PCM

87) In a terrestrial microwave system transmission of signals is achieved through-

a) reflection from the ionosphere

b) line of sight mode

c) reflection from the ground

d) diffraction from the stratosphere

88) (10110011)2 = (?)8

a) 253 b) 263 c) 273 d) 283

89) A Not gate at the output of AND gate converts AND gate into-

a) NAND b) NOR c) AND d) NOPE.

90) Varactor diode is a

a) Variable inductor

b) Variable capacitor

c) Variable rectifier

d) Variable amplifier


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91) One of the following material which has negative temperature coefficient of resistance is-

a) Brass

b) Copper

c) Aluminium

d) Carbon

92) One of the following, which is not a transducer in the true sense, is

a) )Thermocouple

b) Piezoelectric pick up

c) )Photo-Voltaic cell

d) LCD

93) The resistance of a metallic wire would

a) Increase as the operating frequency increases.

b) Decrease as the operating frequency increases

c) Remain unaffected on increasing the operating frequency

d) None

94) The antenna most commonly used for TV broadcasting in the UHF band is

a) Turnstile antenna

b) Dipole antenna

c) Yagi antenna

d) Rhombic antenna

95) In a FM receiver, the channel bandwidth is around-

a) 10 KHz b) 20 KHz c) 75 KHz d) 200 KHz

96) A digital frequency counter can be converted to a DVM by addition of a stage of suitable

a) voltage controlled oscillator

b) D/A converter to it

c) power amplifier to it

d) Operational amplifier to it.

97) The temperature coefficient of resistance for a thermistor is

a) low and negative

b) low and positive

c) high and negative

d) high and positive

98) Which of the following types of transducers can be used for measurement of an angular

position is

a) Circular potentiometer

b) Synchro

c) E-pick off

d) both a and b


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99) A 300V full-scale deflection voltmeter has an accuracy of 2 %. When it reads 222V.

The actual voltage

a) Lies between 217.56V and 226.44V

b) Lies between 217.4V and 226.6V

c) )Lies between 216V and 228V

d) )Is exactly 222V

100) For signal amplitude modulated to a depth of 100 % by a sinusoidal signal power is-

a) Same as the power of unmodulated carrier

b) Twice as the power of unmodulated carrier

c) 3/2 times the power of unmodulated carrier

d) 2/3 times the power of unmodulated carrier

101) Identify the false statement about MOSFET. It can operate in-

a) Depletion mode

b) Enhancement modes

c) Depletion and enhancement modes

d) Depletion only mode

102) Identity wrong rule for binary subtraction ?

a) 0 0 = 0

b) 1 0 = 1

c) 1 1 = 0

d) 0 1 = -1 with borrow of 1

103) In a PCM system, the number of quantization level are 16 and the maximum signal

frequency is 4KHz. The bit transmission rate is-

a) 64 K bits / sec

b) 32 bits / sec

c) 32 K bits /sec

d) 16K bits /sec

104) The reverse saturation Current ICO in a transistor amplifier-

a) doubles for every 100C rise in temperature

b) doubles for every 50C rise in temperature

c) doubles for every 10C rise in temperature

d) increases linearly with temperature


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105) Synchro is a

a) Transducers

b) Amplifier

c) Motor

d) Transformer

106) Modulation is not used to-

a) Reduce the bandwidth used

b) Separate differing transmissions

c) Ensure that intelligence may be transmitted over long distances

d) Allow the use of practicable antennas

107) In active low logic, the logic I state corresponds to-

a) high voltage level

b) low voltage level.

c) negative voltage

d) ground level.

108) If JK inputs are tied together, the circuit reduces to-

a) SR FF

b) D FF

c) T FF

d) JK FF

109) For designing half adder are require-

a) a NOT gate and a OR gate

b) a AND gate and a OR gate

c) two AND gate

d) AND gate and a EXOR gate

110) In a semiconductor the measurement of Hall coefficient provides information on the

a) Sign and mass of charge carriers

b) Mass and concentration of charge carriers

c) Sign of charge carries alone

d) Sign and concentration of charge carriers

111) The series equivalent resistance value in case of a lossy capacitor will be

a) Very small

b) Small

c) Large

d) None


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112) Resistivity of a conductor depends upon its

a) Resistance

b) Length

c) Area of cross section


113) Length of a conductor is halved. Its conductivity will be

a) Halved

b) Unchanged

c) Doubled

d) Quadrupled

114) 3 resistance of 10 , 5, 2 are connected in parallel .Net resistance will be

(a) More than 10 (b) Between 10 and 5 (c )Between 5and2 (d) less

than 2

115) Which of the following is true when cells are connected in series

a) Current capacity increases

b) Current capacity decreases

c) EMF increases

d) Current capacity decreases

116) A heater is marked 1000 w. the energy consumed by it in 1 hour is

(a) 1J (b) 1KJ (c) 1KWh (d) 1Wh

117) The length and area of cross section of a conductor are doubled, its resistance

a) Halved

b) Unchanged

c) Doubled

d) Quadrupled

118) Two unequal resistances are connected in parallel across a cell. Which of the

following statement is true ?a) Same current is set up in both resistors.

b) Current through smaller resistor is more

c) current through larger resistor is more

d) Any of the above

119) Diodes are used in rectifier circuits because

a) they have unidirectional conducting properties

b) they have bidirectional conducting properties

c) they have no conducting property


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120) Which one is the most sensitive device to light.

a) Photodiode

b) Phototransistor

c) pn junction diode

d) Bipolar junction transistor


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electronics let exam.2008.doc