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Posted Date: 05 Jul 2008 Posted By:: jothi vignesh Member Level: Gold Points: 5 (Rs. 1)
2005 Anna University Chennai B.E. Electrical and Electronics Engineering Third Semester Question paper
B.E./B.Tech. DEGREE EXAMINATION
Electrical and Electronics Engineering
EC 253 — ELECTRON DEVICES
Time : Three hours Maximum : 100 marks
Answer ALL questions.
PART A — (10 ? 2 = 20 marks)
1. An electron is injected perpendicularly into a uniform magnetic field of flux
density 0.01 Wb/m2 with an initial speed of 107 m/s. What will be the radius of
the circular path that the electron describes?
2. An ideal Germanium diode has a reverse saturation current of 20 ? A. Find
the dynamic resistance for a forward bias of 0.1 V.
3. What is Hall effect? Give any two applications.
4. What are hybrid parameters?
5. Define diffusion current.
6. Give any two ways by which the transistors are protected from overheating
due to high power operation.
7. What are the advantages of FETs?
8. Mention any two applications of SCR.
9. What is an optoelectronic coupler?
10. Draw the basic structure of a CRT.
PART B — (5 ? 16 = 80 marks)
11. (i) Explain about magnetic deflection in a CRT. Derive the expression for
deflection sensitivity. (10)
2 D 033
(ii) Find the speed of an electron after it has moved through a potential
difference of 10,000 V. What would be the percentage change in its mass
at this speed? (6)
12. (a) (i) Explain the origin of depletion layer capacitance and diffusion
capacitance and discuss the importance of each. (8)
(ii) What is a Schottky diode? What is its application? (8)
(b) (i) You are given two different Ge diodes with their data at forward
bias as follows :
VD(on)1 = 0.7 V at 10 mA
VD(on)2 = 0.6 V at 0.1 mA.
If these diodes are placed in a series circuit and a current of 1 mA is
made to flow in them (forward bias), what will be the sum of voltage
drops across them? (8)
(ii) Explain with relevant diagrams, the function of a Zener diode.
Mention its important applications. (8)
13. (a) (i) Draw the hybrid ? model of a transistor in CE configuration and
discuss about each component of the model. (10)
(ii) Draw the Ebers–Moll model for a pnp transistor. (6)
(b) (i) With appropriate diagrams, discuss about various switching times
of a transistor. (8)
(ii) Compare the three configurations of a transistor. (8)
14. (a) Explain the function of depletion type MOSFET.
(b) (i) Describe the operation of UJT. What is its main application? (10)
(ii) Draw the low frequency small signal JFET model. (6)
15. (a) With neat sketches, discuss about the basic construction and operation of
a laser diode. Name the different types of lasers.
(b) What is a photo diode? With proper characteristic curves and relevant
diagrams, explain the operation of the device. What are its applications?
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