2010 Anna University Chennai B.E Computer Science and Engineering Ec 2151 — Electric Circuits and Electron Devices Question paper

B.E./B.Tech. DEGREE EXAMINATION, NOVEMBER/DECEMBER 2010
Second Semester

Computer Science and Engineering

EC 2151 — ELECTRIC CIRCUITS AND ELECTRON DEVICES

(Common to Biomedical Engineering, Electronics and Communication Engineering
and Information Technology)

(Regulation 2008)
Time : Three hours Maximum : 100 Marks
Answer ALL questions

PART A — (10 × 2 = 20 Marks)

1. Find Req of the restive network .
2. Determine the current drawn by the source as shown in
3. For the circuit shown in fig.3 determine the value of Q at resonance and Bandwidth of the circuit.
4. A Series RC circuit consists of resistor of 10 and a capacitor of 0.1F as shown in Fig.4. A constant voltage of 20v is applied to the circuit at t=0. Determine voltage across resistor and capacitor.
5. State Mass-Action law.
6. Define diffusion capacitance.
7. Define Base width modulation and bring out its consequences.
8. Mention the advantages of MOSFET over JFET.
9. Draw the two transistor model of an SCR with its characteristic curve.
10. Under what principle does a photo voltaic cell work?

PART B — (5 × 16 = 80 Marks)

11. (a) (i) Use Thevenin's theorem to find the current through 5 resistor (Marks 8) (ii) Find the voltage across 2 resistor in fig.6 by using super position
theorem. (Marks 8)
Or
(b) (i) Determine current flowing through the 5 resistor in the circuit Norton theorem. (Marks 8)
(ii) Determine the maximum power delivered to the load in the circuit (Marks 8)

12. (a) (i) Find the complete solution for the current in a RLC circuit for a sinusoidal input. (Marks 8)
(ii) The circuit consists of R = 10, L = 0.5 H and C = 200 µ F. If the switch is closed when f = 30°. Determine the current equation. (Marks 8)
Or
(b) (i) Consider the single tuned circuit
1. Resonant frequency
2. Output voltage at resonance and
3. Maximum output voltage.
Assume Rs>>wrL, and k=0.9. (Marks 8)
(ii) With neat diagram, obtain gain of a double tuned amplifier with critical value of mutual inductance. (Marks 8)

13. (a) (i) State continuity equation and prove that concentration of changes is independent of time with zero electric field. (Marks 8)
(ii) With neat diagram, explain the formation of PN junction and derive its depletion width. (Marks 8)
Or
(b) (i) What is the breakdown mechanism found in Zener diode? Explain it with neat diagram. (Marks 8)
(ii) Write detailed notes on space charge and diffusion capacitance. (Marks 8)

14. (a) Explain the construction and working principle of a JFET and obtain its characteristic parameters. (Marks 16)
Or
(b) Explain the operation of a Depletion mode MOSFET and its comparison over enhancement MOSFET with neat diagrams. (Marks 16)

15. (a) Discuss the construction and operation of a Tunnel Diode with neat energy band diagram. (Marks 16)
Or
(b) Write detailed notes on:
(i) DIAC and TRIAC (Marks 5)
(ii) Photodiode and Phototransister (Marks 5)
(iii) LED and LCD (Marks 6)

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