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UGC NET DEC 2008 : ELECTRONIC SCIENCE PAPER III

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Signature and Name of Invigilator Roll No. (In figures as per admission card) 1. (Signature) (Name) Roll No. 2. (Signature) (Name) Test Booklet No. D 8 8 0 8 Time : 2 hours] (In words) PAPER III ELECTRONIC SCIENCE Number of Pages in this Booklet : 32 [Maximum Marks : 200 Number of Questions in this Booklet : 26 Instructions for the Candidates U U 1. Write your roll number in the space provided on the top of this page. 1. U DU U S U U U U U 2. U U U, U S U U 2. Answers to short answer/essay type questions are to be given in the space provided below each question or after the questions in the Test Booklet itself. U U No Additional Sheets are to be used. 3. U U U, - S U U U - S U U 3. 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) - S U U U U U U U S U U- U S S U U (i) To have access to the Test 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) 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 (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. 4. U U 4. Read instructions given inside carefully. 5. One page is attached for Rough Work at the end of the booklet before the Evaluation Sheet. 5. U U- S (Rough Work) U U DU 6. If you write your name or put any mark on any part of the Answer Sheet, except for the space allotted for the relevant entries, which may disclose your identity, you will render yourself liable to disqualification. 6. U- S U , U U U U 7. U # U U- S U U U U U # U U U U 7. You have to return the Test booklet to the invigilators at the end of the examination compulsorily and must not carry it with you outside the Examination Hall. 8. / U Z U S U 8. Use only Blue/Black Ball point pen. 9. Use of any calculator or log table etc. is prohibited. 9. U ( U U) U U 10. There is NO negative marking. 10. U U D 8808 1 P.T.O. ELECTRONIC SCIENCE PAPER III NOTE : D 8808 This paper is of two hundred (200) marks containing four (4) sections. Candidates are required to attempt the questions contained in these sections according to the detailed instructions given therein. 2 SECTION - I Note : This section contains f ive (5) q uestions based on the following paragraph. Each question should be answered in about thirty (30) words and each carries five (5) marks. (5x5=25 marks) Modern communication systems essentially involve transmission of information available in the form of an electrical signal to a receiver located at another location. Most message signals are low frequency (< 20 kHz) and cannot be transmitted long ~ distances and have to be loaded on a high frequency carrier wave by modulation. The physical medium can be space, as in ionospheric propagation and satellite communication, or a guided channel, like copper cables (with loss ~ 20 dB /km) at low to RF frequency and optical fiber (with loss ~ 0.2 dB/km) for optical communication. The bandwidth at a high carrier frequency is roughly 10% of the carrier frequency and a typical audio and video signal requires a band of 8 kHz and 4.5 MHz respectively. 1. Define Amplitude Modulation and Frequency Modulation. D 8808 3 P.T.O. 2. Why is it difficult to transmit a low frequency signal over long distance as compared to a high frequency signal ? 3. What is ionosphere propagation and what is the typical frequency range in which it is possible ? D 8808 4 4. If 1 mW of power is launched into a copper cable and an optical fiber, estimate the power received after a propagation distance of 50 km in each case. 5. Consider optical communication at l51.5 mm. How many (i) audio and (ii) video channels can be accomodated on a single channel ? D 8808 5 P.T.O. SECTION - II Note : This section contains fifteen (15) questions each to be answered in about thirty (30) words. Each question carries five (5) marks. (5x15=75 marks) 6. For a CE tranistor in active region show that IC 5 b IB + ( b11 ) ICO where all symbols have conventional meanings. D 8808 6 7. State and prove the Superposition Theorem. 8. What is an ideal OP - AMP ? Compare the properties of a 741 IC to those of an ideal OP - AMP. D 8808 7 P.T.O. 9. What are Flags in a microprocessor ? Name four commonly used Flags. 10. Realise a digital circuit for the logic equation y 5A.B1A. B . D 8808 8 11. What is the race round condition in a Flip Flop ? 12. What is a pointer in C language and how is it related to the address operator and indirection operator ? D 8808 9 P.T.O. 13. Define Directive Gain and Directivity of an Antenna. 14. What modulation index would produce the lowest bandwidth FM signal according to Bessel Functions ? D 8808 10 15. What is Responsity R of a p-i-n photodectector ? How is it related to quantum efficiency h ? 16. Distinguish between spontaneous emission and stimulated emission. D 8808 11 P.T.O. 17. 18. Explain how bunching takes place in a Reflex Klystron. Draw the schematic symbols used for a n-channel and p-channel enhancement mode MOSFET. D 8808 12 19. 20. What is measured by a Venturi Tube ? What is the principle of operation ? What is the Routh - Hurwitz criterion for stability ? D 8808 13 P.T.O. SECTION - III Note : 21. 22. 23. (a) (b) (a) (b) (a) (b) 24 This section contains f ive (5) q uestions. Each question carries twelve (12) marks and is to be answered in about two hundred (200) words. (12x5=60 marks) Explain with necessary diagrams the characteristics of bipolar junction transistors. What is the differnce between Avalanche and Zener breakdown. What is the working principle of a phase-shift oscillator ? Use De Morgan s Theorem to prove that a NOR gate with inverted inputs is equivalent to an AND gate. What is an interrupt ? Discuss the various hardware interrupts of the 8085 miscroprocessor. Explain briefly the 8051 miscrocontroller. What is the relationship between Strain and Stress ? Why are strain measurement s of importance ? (b) Explain with necessary diagram the working principle of any one strain gauge. (a) Write down Maxwell s Equations in a nonconducting medium and show that (b) 25. (a) H and E satisfy the wave equation. The electric field of a plane wave in a dielectric medium with < S > = 3.77 W/m2 is given by E 5 y Eo exp [ j (at - bx - dz ) ] V/m. 2 6 1 with a56p31014 s21, b52 3 p310 m and d52p3106 m21. Obtain the following : (i) frequency and wavelength of the wave. (ii) dielectric constant of the medium. (iii) direction of propagation and polarization of the wave. (iv) D 8808 the corresponding H . 14 D 8808 15 P.T.O. D 8808 16 D 8808 17 P.T.O. D 8808 18 D 8808 19 P.T.O. D 8808 20 D 8808 21 P.T.O. D 8808 22 D 8808 23 P.T.O. SECTION - IV Note : This section consists of one essay type question of forty (40) marks to be answered in about one thousand (1000) words, [each part carries ten (10) marks]. (40x1=40 marks) 26. (a) What is a shift register ? What are the differences between parallel loading and serial loading in shift registers ? (b) What are different types of address modes available in the 8085 microprocessor ? Explain with examples. (c) What is a thyristor ? Draw and explain the v-i characteristics of a thyristor. (d) Explain with simple ray theory light guidance in a multimode step index fiber. Obtain the expression for time delay between the fastest and slowest ray and explain how this effects the transmission data rate. OR (a) With a suitable sketch describe the construction of a microwave pin diode. Breifly explain its operation for microwave detection. (b) Draw the block diagram of a Ripple Counter. Sketch the waveforms at the output of each FLIP FLOP for a three stage counter. (c) Explain amplitude, frequency and phase modulation. What is the modulation index in each case ? (d) Explain the use of an UJT as a relaxation oscillator. What is the term intrinsic stand-off ratio ? D 8808 24 D 8808 25 P.T.O. D 8808 26 D 8808 27 P.T.O. D 8808 28 D 8808 29 P.T.O. D 8808 30 D 8808 31 P.T.O. FOR OFFICE USE ONLY 1 26 51 76 2 27 52 77 3 28 53 78 4 29 54 79 5 30 55 80 6 31 56 81 7 32 57 82 8 33 58 83 9 34 59 84 10 35 60 85 11 36 61 86 12 37 62 87 13 38 63 88 14 39 64 89 15 40 65 90 16 41 66 91 17 42 67 92 18 43 68 93 19 44 69 94 20 45 70 95 21 46 71 96 22 47 72 97 23 48 73 98 24 49 74 99 25 50 75 Marks Obtained Question Number Marks Obtained Question Number Marks Obtained Question Number Marks Obtained Question Number Marks Obtained 100 Total Marks Obtained (in words) ..................................... (in figures) .................................... Signature & Name of the Coordinator ............................... (Evaluation) D 8808 Date ............................. 32

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