Anna University Chennai 2005 B.E Electrical and Electronics Engineering Third Semester - exam paper

B.E./B.Tech. DEGREE EXAMINATION,
Third Semester
Electrical and Electronics Engineering
EC 253 — ELECTRON DEVICES
Time : 3 hours Maximum : 100 marks
ans ALL ques..
PART A — (10 ? two = 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. obtain
the dynamic resistance for a forward bias of 0.1 V.
3. What is Hall effect? provide any 2 applications.
4. elaborate hybrid parameters?
5. describe diffusion current.
6. provide any 2 ways by which the transistors are protected from overheating
due to high power operation.
7. elaborate the advantages of FETs?
8. Mention any 2 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) discuss about magnetic deflection in a CRT. Derive the expression for
deflection sensitivity. (10)
D 033
2 D 033
(ii) obtain 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) discuss the origin of depletion layer capacitance and diffusion
capacitance and explain the importance of every. (8)
(ii) What is a Schottky diode? What is its application? (8)
Or
(b) (i) You are provided 2 various 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 one mA is
made to flow in them (forward bias), what will be the sum of voltage
drops across them? (8)
(ii) discuss 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
explain about every component of the model. (10)
(ii) Draw the Ebers–Moll model for a pnp transistor. (6)
Or
(b) (i) With improper diagrams, explain about different switching times
of a transistor. (8)
(ii) Compare the 3 configurations of a transistor. (8)
14. (a) discuss the function of depletion kind MOSFET.
Or
(b) (i) define 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, explain about the basic construction and operation of
a laser diode. Name the various kinds of lasers.
Or
(b) What is a photo diode? With proper characteristic curves and relevant
diagrams, discuss the operation of the device. elaborate its applications?

Earning:   Approval pending.