PAPER-II
ELECTRONIC SCIENCE


1. Which diode exhibits negative
resistance characteristics
Zener diode
Tunnel diode
Schottky diode
p-n junction diode
2. The effective mass of an electron in a
band with a given relationship
is given by
<img src='./qimages/2237-6.jpg'>

3. Transient response occurs in
resistive circuit
reactive circuit
steady state
open circuit
4. Superposition theorem is not valid
for
Voltage responses
Current responses
Power responses
Phase responses
5. A field effect transistor is a
current controlled device
voltage controlled device
gain controlled device
drain controlled device
6. A differential amplifier is invariably
in the input stage of all Op-Amps.
This is done basically to provide the
Op-Amps with a very high
CMRR
bandwidth
slew rate
open-loop gain


7. In a JK flip-flop the output state will
toggle only when
J K 0 J K 1
J K 0 J K 1
8. D to A converter is achieved by
ladder network
dual-slope conversion
astable multivibrator
voltage controlled oscillator
9. Which interrupt has highest priority
in 8085
RST 7.5 RST 6.5
RST 5.5 TRAP
10. A 4-bit data size is called
data bus baud
byte nibble
11. The storage medium for the static
storage class is
CPU register
memory
accumulator
stack
12. In executable program is created by
compiler only
linker only
compiler and linker
editor
13. The cut off frequency for TEM wave is
infinity
zero
arbitrary frequency
that of TE10
14. Depth of penetration of
electromagnetic wave in free space is
infinity
1
a
0 a



15. Which of the following communication modes support two-way traffic but in only one direction at a time

Simplex


Half-duplex


Three-quarter duplex


Full-duplex



16. Intermediate frequency is used in

AM transmitter


FM transmitter


Super heterodyne receiver


Frequency division multiplexing



17. Relaxation oscillator is made using

SCR FET


UJT BJT



18. Which can measure pressure directly

Thermistor


Bourdon tube


LVDT


Strain gauge



19. Bandwidth offered by optical fiber communication is of the order of

40 THz 40 GHz 1010 Hz


40 MHz



20. In feed-back control system, over-damped condition for damping ratio will be equal to

one


greater than one


less than one


zero



Directions Q. Nos. 21 to 30 Assertion Reasoning type.
The following questions consist of two statements one labelled as "Assertion and the other labelled as "Reason You are to examine these two statements carefully and decide if the Assertion and the Reason are individually true and if so, whether the Reason is a correct explanation of the Assertion. Select your answers to these items using the codes given below and mark your answer accordingly.

Codes

Both and are true and

is the correct explanation of



Both and are true, but

is not the correct explanation of



is true, but is false.


is false, but is true.


21.
Assertion At room temperature, the Fermi level in a p-type semiconductor lies above the valance band, whereas that in the n-type semiconductor lies below the conduction band.

Reason At room temperature, the p-type semiconductor is rich in holes whereas the n-type semiconductor is rich in electrons.

22.
Assertion Thevenin's theorem is normally used to find the equivalent voltage source and Thevenin's equivalent resistance of a complex network.

Reason Thevenin theorem holds good for d.c. voltages but not for a.c. voltages.

23.
Assertion In the normal operation of BJT the emitter diode and collector diode are forward biased.

Reason In the active region the BJT can provide class-A operation.

24.
Assertion R-2R ladder type D/A converter has a higher speed of conversion than a weighted resistance D/A converter.


Reason R-2R ladder type D/A converter uses a smaller number of passive components than the weighted resistance D/A converter.
25.
Assertion In Intel 8085, the lower type of address and data are multiplexed.

Reason This helps limit the number of external pin terminals.


26.
Assertion User defined functions are available as library functions in C compiler.

Reason User defined functions help to avoid repetition of same group of statements.


27.
Assertion Helical antenna can be used as feeder for large parabolic reflectors to obtain circular polarization.

Reason Parabolic reflectors reverse the sense of polarization of the wave during reflection.


28.
Assertion In Hall effect, the open circuit transverse voltage developed by a current carrying semiconductor with a steady magnetic field imposed perpendicular to the current direction has opposite signs of n-type and p-type semiconductors.

Reason The magnetic field pushes both the holes and the electrons in the same direction.


29.
Assertion Optical fiber have broader bandwidth compared to conventional copper cables.

Reason The information carrying capacity of optical fibers is limited by dispersion and non­linear effects.


30.
Assertion Routh-Hurwitz criter­ion deals with stability of the system.


Reason Change of sign in the first column of Routh array suggests stability of the system.

31. Consider the devices.
1. JFET 2. MOSFET
3. BJT 4. CMOS The correct sequence in which the input impedance decreases is

3 2


3 3


32. Consider the following steps
1.
Etching

2.
Exposure of ultra violet radiation

3.
Stripping

4.
Developing After a wafer has been coated with photoresist, the correct sequence of these steps in photolithography is



1 3


3 1


33. Voltage regulator ICs are mentioned below
1. 7809 2. 7805
3. 7815 4. 7812 The correct sequence in which the output increases is

3 4


2 1


34. Consider the following communication systems
1.
Telephony

2.
Radio communication

3.
Microwave communication

4.
Optical communication The correct sequence of these systems from the point of view of increasing order of base band channels each one of them can accommodate is



1 2


4 3


35. Given below is a data size
1. Byte 2. Nibble
3. Double Word 4. Word
The correct sequence in decreasing order of data size is

2 2


1 1


Direction Q. Nos. 36 to 45
In the following question, match List-I
with List-II and select the correct answer
using the codes given below the lists


36. List I List II

BJT Trans­conductance


JFET Breakdown diodes


Avalanche (iii) Photo masking effect


IC Emitter fabrication follower


Codes





(iii)










37. List I List II

Laplace stability


Poles and current zeros source


Norton's short circuit theorem


y-parameters transient analysis


Codes





(iii)










38. List I List II

Positive voltage voltage series regulators


JFET 78 XX


Feedback (iii) Regenerative feedback


Multivibrator Voltage variable resistor


Codes





(iii)










39. List I List II

Fan out of 10 Mod-2 addition


XOR Counter


Dual slope TTL


Modular-10 A-D conversion


Codes



(iii)












40. List I List II

8085 Handshake mode


8031 2-key lockout


8279 SID


8255 O-KBROM


Codes



(iii)












41. List I List II

x Post increment


while character


x infinite loop


hex


Codes












(iii)



42. List I List II

Capacitive Pressure transducer


Thermocouple Strain


Load cell Displacement


Diaphragm Temperature


Codes
















43. List I

Frequency Modulation


Double side suppressed carrier


PCM


Amplitude modulation


Codes
















44. List I

LASER


Solar cell


Photo diode


LED


Codes
















45. List I

Proportional control


On-off control


Bode plot


Routh-(iv) Hurwitz


Codes
















List II
Envelop
detection
Companding
Balanced
modulator
Pre­
emphasis
and de­
emphasis











List II Emits light of low intensity Consumes electrical power due to the incident light Delivers power to load Emits high energy coherent beam













List II
hysteresis
stability
variable gain amplifier frequency response












Read the paragraph and answer the questions 46 to 50. Power devices with pnpn layers such as SCR, SCS and GTO belong to thyristor series. However, UJT is also a member of this group. The most popular pnpn device the SCR was introduced in 1956 by Bell Telephone Laboratories. It has capability to control power as high as 10 MW with individual ratings upto 2000 A at 1800 V. The frequency range of its application has also been extended upto 50 KHz hence it is used in induction heating and ultrasonic cleaning. A simple p-n junction diode is a rectifier without control action. SCR is a rectifier with control action. The third element called gate enables the controlled rectification gate is used to turn the SCR on but not to turn it off. In the off state the resistance of SCR is large upto 100 KO while in the on state its dynamic resistance is typically 0.01 to 0.1 O. As it has to handle high power and high temperature, SCR is made of Si. To turn the SCR on a positive pulse of suitable amplitude must be applied to the gate terminal when the anode is positive with respect to the cathode. However, removal of gate signal does not turn the SCR off. The general methods used for turning the SCR off are anode current interruption and forced commutation. It is not recommended to turn the SCR on with zero gate signal. The specifications of SCR given in the data sheet include forward break-over voltage, latching current, holding current, reverse break-down voltage, turn-on time, turn-off time, gate ratings and junction temperature Tj.
Some of the applications of SCR are motor controls, relay controls, inverters, cycloconverters, preventive circuits, regulated power supplies and phase control. Another pnpn device having characteristic similar to that of SCR is SCS silicon controlled switch. However it has two gate terminals. The additional gate at the anode side can be used to turn SCS off. The turn off time of SCS is 1 to 10 µs as against 5 to 30 µs for that of SCR. Other advantages of SCS over SCR are
1.
increased control

2.
triggering sensitivity and

3.
more predictable firing


At present SCS is limited to low power current and voltage ratings. It can dissipate 100 to 500 mW power. Some of the applications of SCS are pulse generation, voltage sensing and oscillators. Gate turn off switch is one more pnpn device which can be turned on or off with cathode gate. The gate current requirement of GTO is greater than that for SCR but its turn off time µs) is much smaller than that for SCR. This makes GTO a faster device. Some of the applications of GTO are counters, pulse generators, multivibrators and voltage regulators.
Light activated SCR is turned on by the light falling on the gate. It is used as a relay, optical light controller, phase controller and motor control device. An interesting application of LASCR is in AND and OR circuits. One more pnpn device is Shockley diode which can be used as trigger switch for SCR like UJT. A diac is also used for triggering and it provides triggering in either direction.

A device that can control ac power to the load during the positive and negative cycles of input is called triac. It is basically a diac with a gate terminal for bilateral turn on.
46. In the ON state the voltage drop across the SCR is approximately equal to

Anode voltage


Cathode voltage


1 to 1.5 V


Gate voltage


47. For complete isolation between load and signal which device is preferred

Diac LASCR


SCR Triac


48. Which device is useful for high frequency application

SCS GTO


Triac SCR


di

49. There is a danger of failure of SCR
dt

if it is triggered with gate
current.

positive


negative


zero


sinusoidal


50. Forced commutation is employed when anode voltage is

dc


ac


pulsating


triangular


Space For Rough Work