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UGC NET DEC 2008 : ELECTRONIC SCIENCE PAPER II

16 pages, 50 questions, 50 questions with responses, 74 total responses,

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Signature and Name of Invigilator OMR Sheet No. : ...................................................... (To be filled by the Candidate) 1. (Signature) Roll No. (Name) (In figures as per admission card) Roll No. 2. (Signature) (In words) (Name) Test Booklet No. D 8 8 0 8 PAPER II ELECTRONIC SCIENCE Time : 1 hours] Number of Pages in this Booklet : 16 Number of Questions in this Booklet : 50 U Instructions for the Candidates 1. 2. 3. 4. 1. U DU U S U U U U Write your roll number in the space provided on the top of this page. This paper consists of fifty multiple-choice type of questions. At the commencement of examination, the question booklet will be given to you. In the first 5 minutes, you are requested to open the booklet and compulsorily examine it as below : (i) To have access to the Question Booklet, tear off the paper seal on the edge of this cover page. Do not accept a booklet without sticker-seal and do not accept an open booklet. (ii) Tally the number of pages and number of questions in the booklet with the information printed on the cover page. Faulty booklets due to pages/questions missing or duplicate or not in serial order or any other discrepancy should be got replaced immediately by a correct booklet from the invigilator within the period of 5 minutes. Afterwards, neither the question booklet will be replaced nor any extra time will be given. (iii) After this verification is over, the Test Booklet Number should be entered in the OMR Sheet and the OMR Sheet Number should be entered on this Test Booklet. Each item has four alternative responses marked (A), (B), (C) and (D). You have to darken the oval as indicated below on the correct response against each item. Example : A B C 2. - 3. U U U, - S U U U - S U (i) - S U U U U S U U- U S S U U (ii) U DU U U U - S DU U U U U U U S DU / U U U U U S S U U U U U S U U - S U U - S U UQ (iii) - S R OMR U U U U OMR R - S U U 4. U U (A), (B), (C) (D) U U U U U D A B C D (C) U 5. U U I U U- U where (C) is the correct response. 5. Your responses to the items are to be indicated in the Answer Sheet given inside the Paper I booklet only . If you mark at any place other than in the ovals in the Answer Sheet, it will not be evaluated. 6. Read instructions given inside carefully. 7. Rough Work is to be done in the end of this booklet. 8. If you write your name or put any mark on any part of the test booklet, except for the space allotted for the relevant entries, which may disclose your identity, you will render yourself liable to disqualification. 9. You have to return the test question booklet to the invigilators at the end of the examination compulsorily and must not carry it with you outside the Examination Hall. 10. Use only Blue/Black Ball point pen. 11. Use of any calculator or log table etc., is prohibited. 12. There is NO negative marking. D 8808 [Maximum Marks : 100 U U U S U U U , U 6. U U 7. (Rough Work) S DU U U 8. U- S U , U U U U 9. U # U U- S U U U U U # U U U / U Z U S U 11. U ( U U) U U 12. U U 10. 1 P.T.O. ELECTRONIC SCIENCE PAPER II Note : 1. This paper contains fifty (50) objective-type questions, each question carrying two (2) marks. Attempt all of them. Tunnel diode, with its negative resistance characteristics can be employed for : (A) (B) Voltage Amplification (C) 2. Current Amplification Power Amplification (D) All the above When a semiconductor is heavily doped in a range of 1017 to 1018 impurity atoms/cm3, then it behaves as : (A) (B) Extrinsic semiconductor (C) 3. Intrinsic semiconductor Simply as a semiconductor (D) Degenerate semiconductor In a series resonance circuit (RLC) : (A) (B) Maximum voltage occurs across the C and L above the resonance frequency (C) Maximum voltage occurs across C below resonance frequency and L above resonance frequency (D) 4. Maximum voltage occurs across the C and L below resonance frequency Maximum voltage occurs across C above resonance frequency and L below resonance frequency Which theorem states that in any network if the voltage sources, V1, V2..............Vn in series with internal resistances R1, R2..............Rn, respectively are in parallel, then the sources can be replaced by a single voltage source in series with single resistance R ? (A) (B) Tellegen s theorem (C) 5. Millmann s theorem Compensation theorem (D) Norton s theorem The ripple factor of a half-wave rectifier is found to be : (A) D 8808 1.57 (B) 1.21 (C) 2 1.12 (D) 1.41 6. The CMRR (Common Mode Rejection Ratio) for a differential amplifier should be : (A) 7. 5 (B) unity (C) small (D) large 15 (C) 10 (D) 20 A. B. C (C) A 1 B1C (D) A.B.C is equivalent to : A .B .C (A) 9. (B) The number of flip-flops required to divide a frequency by 32 is : (A) 8. zero A 1 B1C (B) The 8086 microprocessor can be made to operate in single stepping mode by setting : (A) (B) the overflow status flag (C) 10. the direction status flag the parity status flag (D) the trap status flag Which of the following ports of 8255 supports bi-directional data transfer function ? (A) (B) Port - B (C) 11. Port - A Port - C upper (D) Port - C lower For a statement DO 100 I 5 L, M, N, the number of iterations will be : (A) (C) 12. (M 2L) N 12 (M2L) N (B) 11 (M2L) N (D) 11 (M1L) N What is the error in the given code ? int*p; *p 5 12.9; (A) pointer p is of type int but is assigned real value (B) pointer p is un-initialized, thus can cause error while execution. (C) no error in code (D) all the above D 8808 3 P.T.O. 13. In a copper conductor the electromagnetic wave at 100 MHz penetrates to a depth of 7mm. The wavelength of the electromagnetic wave is : (A) 14. (C) 22 m m 1/r (B) 1/r 2 (C) 1/r 3 5 kHz (B) 105kHz (C) 10kHz OR gate (B) AND gate (C) NOT gate 44 m m (D) 1/r 4 (D) 20kHz (D) XOR gate The wavelength region 1.55mm is important in optical communication because : (i) it can be detected by a Si p-i-n diode (ii) it corresponds to minimum attenuation (iii) it corresponds to minimum dispersion (iv) it can be amplified optically (A) (i), (ii) are correct (B) (ii) and (iii) are correct (C) 18. (D) In high speed TDM, the channels are separated in the receiver by employing : (A) 17. 14 m m Given a carrier frequency of 100 kHz and a modulation of 5 kHz, the bandwidth of AM transmission is found to be : (A) 16. (B) The radiation field of an antenna at a distance r varies as : (A) 15. 7mm (iii) and (iv) are correct (D) (ii) and (iv) are correct Consider the following statements : Thyristors can be turned off by (i) reducing the current below the holding current value (ii) applying a negative voltage to the anode of the device (iii) reducing the gate current Of these statements : (A) (i) and (ii) are correct (B) (i) and (iii) are correct (C) (ii) and (iii) are correct (D) (i), (ii) and (iii) are correct D 8808 4 19. An increase in pH value above 7.0 indicates : (A) (B) decreasing alkalinity (C) 20. increasing alkalinity increasing basicity (D) decreasing basicity A causal discrete time system is stable if the poles of its transfer function lie : (A) outside the unit circle (B) on the unit circle (C) within the unit circle (D) anywhere over the unit circle Question (21 to 30) : The following items consist of two statements, one labelled the Assertion (A) and the other labelled the Reason (R) . You are to examine these two statements carefully and decide if the Assertion (A) and the Reason (R) 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 : (A) (B) Both (A) and (R) are true but (R) is not the correct explanation of (A). (C) (A) is true but (R) is false (D) 21. Both (A) and (R) are true and (R) is the correct explanation of (A). (A) is false but (R) is true Assertion (A) : The depletion mode MOSFET is widely used in digital switching circuits. Reason (R) : 22. Assertion (A) : A circuit containing reactances is said to be in resonance if the voltage across the circuit is inphase with the current through it. Reason (R) : 23. For depletion mode the region between the two heavily doped n+ regions of the MOSFET is made up of lightly doped n material. At resonance, the power factor of the circuit is zero. Assertion (A) : A monostable multivibrator can be used to alter the pulse width of a repetitive pulse train. Reason (R) : D 8808 Monostable multivibrator has a single stable state. 5 P.T.O. 24. Assertion (A) : The output of an 8-bit A to D convertor is 80H for an input of 2.5V. Reason (R) : 25. Assertion (A) : A ROM with an access time of the order of hundreds of nanoseconds is suitable for a control memory. Reason (R) : 26. The efficiency is higher because transistors are used between ON and OFF states. Assertion (A) : Optical Fibres offer a very large communication bandwidth. Reason (R) : 30. AM results in an increase in signal power. Assertion (A) : A switched mode power supply is a high efficiency dc-dc converter with an unregulated input dc voltage and a regulated output voltage. Reason (R) : 29. In a good dielectric the conduction current is very small. Assertion (A) : AM has better noise performance than FM. Reason (R) : 28. The time taken to execute an operation in a micro-programmed computer is critically dependant on the access time of the control memory. Assertion (A) : In a good conductor skin depth decreases with frequency as f21/2 while in a good dielectric it decreases as f21 Reason (R) : 27. ADC has an output range of 00 to FFH for an input range of 25V to 1 5V. Frequency of the optical carrier wave is hundreds of THz. Assertion (A) : A Routh-Hurwitz criterion can be applied for stability analysis of feedback control systems with transportation lag. Reason (R) : D 8808 The Routh-Hurwitz criterion is an analytical method for stability analysis. 6 31. The various microprocessor chips which operate at different speeds are : (i) P - III (ii) P - II (iii) 8085 (iv) 8086 The correct sequence according to their speed of operation in increasing order is : (A) (ii) (iii) (iv) (B) (iii) (iv) (ii) (i) (C) (iv) (iii) (i) (ii) (D) 32. (i) (ii) (i) (iii) (iv) Which is the correct sequence in the generation of pulse code modulation ? (i) (ii) converting to PAM (iii) Quantizing (iv) Encoding (A) (i) (ii) (iv) (iii) (B) (i) (iii) (ii) (iv) (C) (i) (ii) (iii) (iv) (D) 33. sampling (iv) (iii) (ii) (i) Below are listed some electromagnetic waves. (i) Microwaves (ii) Visible light (iii) X-Rays (iv) Radiowaves The correct sequence of their frequencies in increasing order is : (A) (i) (ii) (iii) (iv) (B) (i) (ii) (iv) (iii) (C) (iv) (i) (ii) (iii) (D) (iv) (i) (iii) (ii) D 8808 7 P.T.O. 34. Listed below are some communication systems. (i) Radar (ii) Telegraphy (iii) Satellite communication (iv) Telephony The correct sequence of their development in time, with earliest first, is : (A) (iv) (i) (iii) (B) (i) (iii) (ii) (iv) (C) (iii) (ii) (i) (iv) (D) 35. (ii) (ii) (iv) (iii) (i) Listed below are some semiconducting materials. (i) Silicon (ii) Germanium (iii) Gallium Arsenide (iv) Indium Phosphide The correct sequence in order of increasing band gap is : (A) (ii) (i) (iii) (iv) (B) (ii) (i) (iv) (iii) (C) (iv) (i) (ii) (iii) (D) (i) (ii) (iii) (iv) D 8808 8 Question No. 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 (a) Voltage controlled (i) Unijunction transistor (b) Current controlled (ii) Field Effect transistor (c) Conductivity modulation (iii) Bipolar transistor (d) Negative resistance (iv) IMPATT diode Code : (a) (b) (c) (d) (A) (iii) (ii) (iv) (i) (B) (iii) (ii) (i) (iv) (C) (ii) (iii) (i) (iv) (D) (ii) (iii) (iv) (i) 37. List - I List - II (a) Linearity (i) Superposition Theorem (b) Structure (ii) Norton s Theorem (c) Equivalent circuit (iii) Tellegen s Theorem (d) Bilateral (iv) Reciprocity Theorem Code : (a) (b) (c) (d) (A) (ii) (iv) (iii) (i) (B) (i) (iii) (ii) (iv) (C) (iii) (i) (iv) (ii) (D) (ii) (iii) (i) (iv) D 8808 9 P.T.O. 38. List - I List - II (a) Twisted pair (i) High bandwidth line communication (b) Coaxial cable (ii) Supports transmission radio and TV signals (c) Optical Fiber (iii) CATV systems (d) Broadcast system (iv) Point to point service Code : (a) (b) (c) (d) (A) (iv) (iii) (i) (ii) (B) (iii) (iv) (ii) (i) (C) (i) (ii) (iii) (iv) (D) (ii) (iv) (i) (iii) 39. List - I List - II (a) Multiplexer (i) Sequential memory (b) De-multiplexer (ii) Converts decimal number to binary (c) Shift Register (iii) Data selector (d) Encoder (iv) Routes out many data output with single input Code : (a) (b) (c) (d) (A) (i) (ii) (iii) (iv) (B) (iv) (iii) (ii) (i) (C) (iii) (iv) (i) (ii) (D) (ii) (iii) (iv) (i) D 8808 10 40. List - I List - II (a) Capacitive transducer (i) Pressure (b) Thermocouple (ii) Torque (c) Load cell (iii) Displacement (d) Diaphragm (iv) Temperature Code : (a) (b) (c) (d) (A) (i) (ii) (iii) (iv) (B) (ii) (iii) (i) (iv) (C) (iv) (ii) (iii) (i) (D) (iii) (iv) (ii) (i) 41. List - I List - II (a) Rectangular waveguide (i) TE/TM (b) Dielectric waveguide (ii) TE M (c) Coaxial line (iii) Quasi-TEM (d) Microstrip line (iv) Hybrid Code : (a) (b) (c) (d) (A) (ii) (i) (iii) (iv) (B) (i) (iv) (ii) (iii) (C) (iii) (ii) (i) (iv) (D) (iv) (iii) (i) (ii) D 8808 11 P.T.O. 42. List - I List - II (a) Pyro electric effect (i) Emission of electron from a cathode when light is incident on it (b) Piezo electric effect (ii) Change in colour of a hot body with temperature (c) Photovoltaic effect (iii) Generation of EMF under stress (d) Photo emissive effect (iv) Conversion of light energy into electrical power Code : (a) (b) (c) (d) (A) (ii) (iii) (iv) (i) (B) (ii) (iii) (i) (iv) (C) (i) (ii) (iii) (iv) (D) (iii) (i) (iv) (ii) 43. List - I List - II (a) Modem (i) Microprocessor (b) Pentium (ii) Programming Language (c) C++ (iii) Operating system (d) Linux (iv) Internet Code : (a) (b) (c) (d) (A) (iv) (i) (ii) (iii) (B) (i) (ii) (iii) (iv) (C) (ii) (i) (iii) (iv) (D) (i) (iii) (iv) (ii) D 8808 12 44. List - I List - II (a) Helical Antenna (i) Multiband HF (b) Yagi Antenna (ii) Circular polarisation (c) Log Periodic Antenna (iii) Waveguide (d) Horn Antenna (iv) High Gain Code : (a) (b) (c) (d) (A) (i) (ii) (iv) (iii) (B) (iii) (i) (ii) (iv) (C) (ii) (iv) (i) (iii) (D) (iv) (iii) (i) (ii) 45. List - I List - II (a) Rayleigh scattering (i) Pulse broadening in optical fibers (b) Dispersion (ii) Attenuation in optical fibers (c) Numerical Aperture (iii) Light gathering capacity of fibers (d) Splicing (iv) Joining of fibers Code : (a) (b) (c) (d) (A) (i) (ii) (iii) (iv) (B) (ii) (i) (iv) (iii) (C) (iii) (ii) (i) (iv) (D) (ii) (i) (iii) (iv) D 8808 13 P.T.O. Read the passage below and answer the questions that follow based on your understanding of the passage : Gunn effect is instrumental in the generation of microwave oscillations in bulk semiconductor materials. The effect was found by Gunn to be exhibited by gallium arsenide and indium phosphide. If a relatively small dc voltage is placed across a thin slice of gallium arsenide, then negative resistance will manifest itself under certain conditions. Basically, there consist merely of ensuring that the voltage gradient across the slice is in excess of about 3300 V/cm. Oscillations will then occur if the slice is connected to a suitably tuned circuit. It is seen that the voltage gradient across the slice of GaAs is very high. Hence, the electron velocity is also high so that oscillations will occur at microwave frequencies. The Gunn effect is a bulk property of semiconductors and does not depend, as do other semiconductor effects, on either junction or contact properties. The effect is independent of total voltage or current and is not affected by magnetic fields or different type of contacts. Further, it occurs in n-type materials only so that it must be associated with electrons rather than holes. Since the voltage required was proportional to sample length, it was concluded that the electric field, in volts per centimeter, was the factor determining the presence or absence of oscillations. The frequency of oscillations correspond closely to the time that electrons would take to traverse such a slice of n-type material as a result of the voltage applied. Gallium arsenide is one of a fairly small number of semiconductor materials which, in an n-doped sample, have an empty energy band higher in energy than the highest filled band and the size of the forbidden gap between these two is relatively small. This does not apply to other semiconductor materials such as silicon and germanium. When voltage is applied across the slice, it behaves like a normal positive resistance. However, when the gradient becomes extremely high, the electrons, instead of travelling faster, slow down because they have acquired enough energy to be transferred to the higher band in which the mobility is lower. This gives rise to the name transferred electron effect. Thus the classical case of negative resistance is exhibited as the applied voltage rises past the threshold negative resistance value. The oscillations produced are compatible with the formation and transit time of electron bunches, called domains. These domains are formed due to non-uniform distribution of the doping material throughout the sample of gallium arsenide and the negative resistance phenomenon. Gunn diodes are employed frequently as low and medium power oscillators in microwave receivers and instruments. The majority of parametric amplifiers use Gunn diodes as pump sources. They have the advantage over IMPATT diodes of having much lower noise. High power Gunn oscillators are used as power output oscillators, generally frequency modulated, in a variety of low-power transmitter applications. These include police radar, CW doppler radar etc. 46. Gunn effect is seen in : (A) Silicon (B) Germanium (C) Indium Phosphide (D) metal semiconductor junction D 8808 14 47. For Gunn diodes, gallium arsenide is preferred to silicon because the former : (A) (B) has a higher ion mobility (C) has a suitable band gap (D) 48. has a suitable energy band at a higher level is capable of handling higher powers Negative resistance is obtained with a Gunn diode because of : (A) (B) Avalanche breakdown with the high-voltage gradient (C) electron domain formation at the cathode (D) 49. electron transfer to a less mobile energy level tunnelling across the contact junction Gunn effect in gallium arsenide slice depends on : (A) (B) the applied magnetic field (C) 50. the total applied voltage the total current (D) the applied electric field Which of the following statements are correct ? (i) Gunn effect occurs only in n-type materials (ii) Both electrons and holes participate in Gunn effect (iii) Domain formation is essential for oscillations (iv) Gunn effect is seen in all bulk semiconductors (A) (i) only (B) (i) and (iv) (C) (i), (ii) and (iii) (D) (i) and (iii) -oOo- D 8808 15 P.T.O. Space For Rough Work D 8808 16

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Additional Info : Ugc Net December 2008 Question Paper - Electronic Science Paper II
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