ANNA UNIVERSITY B.E. DEGREE EXAMINATION

Second Semester E & I Engineering

ELECTRON DEVICES

(Common to Instrumentation and Control Engineering)

Time : Three hours Maximum : 100 marks

Answer ALL questions.

PART A — (10 ´ 2 = 20 marks)

1. Draw the basic structure of a CRT.

2. An electron is injected perpendicularly into a uniform magnetic field of flux density 0.01 Wb/m^{2} with an initial speed of 10^{7}m/s. What will be the radius of the circular path that the electron describes?

3. Draw the energy band diagram of *n* type and *p* type semiconductor.

4. Compute the value of diffusion length in a single crystal germanium having 100 if the diffusion constant is 47 cm^{2}/sec.

5. Mention the important features of power transistor.

6. What is Early effect?

7. Draw the equivalent circuit and the V–I characteristics of UJT. Mention the important characteristic of the same.

8. Draw the high frequency equivalent circuit of FET in common source configuration.

9. What is an LCD? Mention its merits and demerits.

10. Discuss briefly about the operation of photo diode.

PART B — (5 ´ 16 = 80 marks)

11. (i) Explain about electrostatic deflection employed in CRT. Derive the necessary expressions. (10)

** **(ii) An electron enters the space between two parallel plates A and B through a small hole in A with an energy of 200 eV at an angle of 60° to A. Calculate the uniform magnetic flux density required to cause the electrons return through another hole set in A at a distance of 0.08 mt from the point of entrance and lying in the same plane as the initial velocity. (6)

12. (a) (i) Derive continuity equation. What are its uses? (10)

** ** (ii) The resistivity of intrinsic germanium at 300°K is 0.47 ohm–mt. Calculate the intrinsic density of electrons and holes if the hole and electron mobilities in germanium are 3600 cm^{2}/volt–sec and

1700 cm^{2}/volt–sec. Also calculate the diffusion coefficient for holes and electrons in germanium at 300°K. (6)

Or

** **(b) (i) Explain about Schottky barrier diode. (10)

** ** (ii) The breakdown voltage of the diode is 10 V. Find the value of for the currents and voltage specified. (6)

13. (a) (i) A silicon transistor shown in circuit has an . Find the region of operation of transistor. Find the value of for which the transistor comes out of saturation. (10)

** ** (ii) Derive hybrid model of a transistor in common emitter configuration. (6)

Or

** ** (b) Describe the operation of a bipolar junction transistor as a switch. How will you improve its performance if it is to be used for high frequency applications? Suggest a method.

14. (a) Draw the volt–ampere characteristic of a JFET and explain about each of the regions of operations of the same with relevant equations.

Or

** **(b) What is a bilateral diode switch? Explain.

15. (a) What is a charge transfer device? From the basic principle, explain its operation.

Or

** **(b) With relevant diagrams, describe about the operation of a solar cell.

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