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ECIL Electronics Electrical exam paper

1. When a inductive coil connected to a 200 V, 50Hz ac supply with 10A current flowing through it dissipates 1000 watts then which of the following will have least value in ohms-

a.) Resistance

b.) Reactance

c.) Impedance

d.) None

2.

Oscillator crystal are made of –

a.) Silicon

b.) Germanium

c.) Quartz

d.) None
3.

For small size, high frequency coils, the most common core material is-

a. )Air

b. )Ferrite

c.) Powdered ion

d.) Steel
4.

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 thecapacitor at a distance from either of the two plates as shown in the given figure then the capacity of the capacitor will become –

a.)

b.) C

c.) 2C

d.) 4C
5.

A superconductor is a –

a.) A material showing perfect conductivity and Meissner effect below a critical temperature

b.) A conductor having zero resistance

c.) A perfect conductor with highest di-magnetic susceptibility

d.) A perfect conductor which becomes resistance when the current density through it exceeds a critical value

6.

When an inductor tunes at 200 KHz with 624 pF capacitor and at 600 KHz with 60.4 pF capacitor then the self capacitance of the inductor would be –

a) 8.05 pF

b) 10.05pF

c.) 16.01pF

d.) 20.01pF
7.

Sparking occur when a load is switched off because the circuit has high –

a.) Inductance

b.) Capacitance

c.) Resistance

d.) None
8.

Sparking between contacts can be reduced by inserting a –

a.) Resistance in the line

b.) Capacitor in series with contacts

c.) Capacitor in parallel with contacts

d.) None
9.

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

a.) Class ’A’

b.) Class ’b’

c.) Class ’C’

d.) None
10.

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
11.

The input gate current of a FET is –

a.) a few microamperes

b.) negligibly small

c.) a few milliamperes

d.) a few amperes
12.

In the following fig. with R = 30k, the value of current through 2 K resistor is –

a.) 25 mA

b.) 40 mA

c.) 25/16 mA

d.) 10 mA
13.

A step recovery diode –

a.) has on extremely short recovery time

b.) conducts equally well in both directions

c.) is mainly used as a harmonic generator

d.) is an ideal rectifiers of high frequency signals
14.

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
15.

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

a.) source

b.) drain

c.) gate

d.) none
16.

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
17.

A typical optical fibre has –

a.) High refractive index core and low refractive index cladding

b.) Low refractive index core and high refractive index cladding

c.) Both a and b

d.) None
18.

In the following figure circuit diagram of an op-amp based is shown. The ratio is equal to –

a.) 9

b.) 11

c.) 10

d.) 21
19.

When a loud speaker is connected across the terminals A and B of the network shown in the fig. then its impedance to obtain maximum power dissipation in it will be –

a.) 3 – j1

b.) 3 + j9

c.) 7.5 + j 2.5

d.) 7.5 – j 2.5
20.

In the lattice network, the value of R for the maximum power transfer to the load –

a.) 5

b.) 6.5

c.) 8

d.) 9

21.

For a lossy transmission line short circuited at the receiving end, the input impedance is given by (Z0 is the characteristic impedance, Ö is the propagation constant and l is the length of the line-

a.) Z0 cot h Öl

b.) Z0 cot Öl

c.) Z0 tan h.Ö l

d.) Z0 tan Öl
22.

The approximate thickness of the radome wall should be –

a.) l

b.) l/4

c.) l/2

d.) l/8
23.

A relatively permanent information is stored in

a. ) ROM

b.) RAM

c.) PROM

d.) Volatile memory

24.

The rise time of the RC network shown in the given figure is approximately equal to –

b.) RC

c.) 2RC

d.) 4RC
25.

If in the network shown in the fig. initially a steady state is attained by closing the switch ’s’ and then if the switch is opened at t = 0, then thecurrent i(t) through the inductor will be –

a.) cos50tA

b.) 2A

c.) 2cos100tA

d.) 2sin50tA
26.

When the p network of figure – I and T-network of figure – II are equivalent then the values of R1, R2 and R3 will be respectively –

a) 9W, 6W and 6W

b.) 6W, 6W and 9W

c.) 9W, 6W and 9W

d.) 6W, 9W and 6W
27.

When the impedance matrices of a two port networks are given by and , then if these two networks are connected in series then the impedance matrix of the resulting two-port network will be –

d.) indeterminate
28.

Joule/coulomb is the unit of -

a.) Electric field potential

b.) Potential

c .) Charge

d.) None of the above
29.

The electric field line and equipotential lines-

a.) Are parallel to each other

b.)Are one and same

c.) Cut each other orthogonally

d.)Can be inclined to each other at any angle
30.

For a lossy transmission line short circuited at the receiving end, the input impedance is given by (When Z0 is the characteristic impendence g is the propagation constant and L is the length of the line

31.

When two equal positive point charges are placed along X- axis at X1 and –X1 respectively then the electric field vector at a point P on the positive Y-axis will be directed-

a.) In the +x direction

b.) In the –x direction

c. ) In the +y direction

d.) In the –y direction
32.

The directions of and in TEM mode transmission line with respect to the direction of propagation are-

a.) Both and are transverse to the direction of propagation

b.) is and are transverse and h has a component in the direction of propagation

c.) is entirely transverse and has a component in the direction of propagation

d. ) is entirely transverse and has a component in the direction of propagation
33.

The lowest TM mode in a rectangular waveguide of cross –section a x b with a>b will be-

a.) TM01

b.)TE10

c.) TM112

d.)TE11

34.

When a transmitter in a free space radiates a mean power of ’p’ watts uniformly in all directions then at a distance d sufficiently far from the source in plane the electric field E should be related to p and d as –

35.

. When a dipole antenna was radiating with some excitation in free space radiating a certain amount of the power v if then this antenna is immersed in a lake where water is non-dissipative but has a dielectric constant of 81, then the radiated power with the same excitation will be

a.) Decrease to finite non-zero value

b.)Remain the same

c. )Increase

d.)Decrease to zero
36.

When a (75 – j40)W load is connected to a coaxial line of Z0 = 75 W at 6MHz then the load matching on the line can be accomplished by connecting-

a.) A short – circuited stub at the load

b.)An inductance at the load

c. )A short circuited stub at a specific distance from the load

d.)none of the above
37.

As compared to analog multimeters, digital multimeters are –

a.) less accurate

b.) more accurate

c.) equally accurate

d.) none.
38.

When a signal of 10 mV at 75 MHz is to be measured then which of the following instruments can be used –

a.) VTVM

b.) Cathode ray oscilloscope

c.) Moving iron voltmeter

d.) Digital multimeter
39.

Which of the following statement is true about two wattmeter method for power measurement in three phase current ?

a.) power can be measured using two wattmeter method only for star connected three phase circuits.

b.) when two meter show indentical readings, in the power factor is 0.5.

c.) when power factor is unit, one of the wattmeter reads zero

d.) when the reading of the two wattmeters are equal but of opposite sign, then the power factor is zero –
40.

When a capacitance transducer has two plates of area 5cm2 each, separated by an air gap of 2mm than the displacement sensitivity in pf/cm due to gap change would be –

a.) 11.1

b.) 44.2

c.) 52.3

d.) 66.3
41.

The Q of a radio coil –

a.) is independent of frequency

b.) increases monotonically as frequency increases

c.) decreases monotonically as frequency increases

d.) increases upto a certain frequency and then decreases beyond that frequency
42.

When a generator of internal impedance and operating at 1GHz feeds a load via a coaxial line of characteristic impedance 50 ohm then the voltage wave ratio on the feed line is –

a.) 0.5

b.) 1.5

c.) 2.5

d.) 1.75
43.

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)
44.

Radiation pyrometers are used for the measurement of temperature in the range of –

a.) -2000C to 5000C

b.) 00C to 5000C

c.) 5000C to 12000C

d.) 12000C to 25000C
45.

In the given figure band structure is shown. It is of –

a.) Gallium Avesenide (GaAs)

b.) Silicon (Si)

c.) Copper (Cu)

d.) Germanium (Ge)
46.

When anode is positive with respect to cathode in an SCR, the numbers of blocked p-n junction is –

a.) 1

b.) 2

c.) 3

d.) 4
47.

The circuit symbol for a GTO is

a. b.

c. d.

48.

In the given fig. mark out the type of Cyclo converters

a.) 1 phase to 1 phase with continuous conduction

b.) 1 phase to 1 phase with discontinuous conduction

c.) step up device

d.) 3 phase to 1 phase device

In the given fig. A-1, C=5, m H and C=20 m F, C is initially charged to 200 V. After the switch.

S is closed at t = 0 the

maximum value of current and the

time at which it reaches this value are respectively.

a.) 400 A, 15.707 mS
49.

b.) 50 A, 30 mS

c.) 100 A, 62.828 mS

d.) 400 A, 31.414 mS

50.

50. In the given circuit the maximum current in the main SCR M can be-

a.) 200 A

b.) 170.7 A

c.) 141.4 A

d.) 70.7 A

51.

The transfer function of an amplifier is given by

The high 3-db frequency of the amplifier will approximately

a.) 5850 KHZ

b.)585 KHZ

c.) 5850 HZ

d.)585HZ

52.

In comparison to full wave rectifier with two diodes the four divide bridge rectifier has the dominant advantage of -

a). Higher current carrying

b.)Lower ripple factor

c.) Higher efficiency

d.)Lower peak increase voltage require

53.

Power output increase in a class-c amplifier-

a.) If the conduction angle decrease

b).If the conduction angle increase

c.) Are not governed by the conduction angle

d.)None of the above
54.

A transistor with hie = 1.5 k and hfe = 75 is used in an emitter follower circuit where R1 and R2 are used for normal biasing . Approximate value of it’s current amplification is-

a.)75

b.)76

c.)75/76

d.)-75
55.

Amplifier of class B has high theoretical efficiency of 78.5 percent because-

a.) It is biased almost to saturation

b.)Its quiescent current is low

c.)It’s output is an exact replica of it’s input

d.)It is biased well below cut off
56.

The coupling that produces minimum interference with frequency response is-

a.) Direct coupling

b.)Impedance coupling

c.) R C coupling

d.)Transformer coupling
57.

In the circuit shown in the given figure Rf provides

a.) Current series feedback

b.)Current shunt feedback

c.) Voltage series feedback

d.)Voltage shunt feedback
58.

Mark the correct relation for the junction transistor

59.

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