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Posted By: jothi vignesh Member Level: Gold Posted Date: 04 Jul 2008
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2007 Anna University B.E Electronics and Communication semester 2 Question paper
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MODEL PAPER
B.E. DEGREE EXAMINATION.
Second Semester
ECE
EC 141 — ELECTRONIC DEVICES
Time : Three hours Maximum : 100 marks
Answer ALL questions.
PART A — (10 ? 2 = 20 marks)
1. What is a flat panel display?
2. 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?
3. Define drift current.
4. Compute the value of diffusion length in a single crystal germanium having
100 ?s if the diffusion constant is 47 cm2/sec.
5. Name the hybrid parameters of a bipolar junction transistor.
6. Write about the mechanisms of breakdown in a pn diode.
7. What is a power MOSFET?
8. What do you mean by direct band gap and indirect band gap materials? Give
examples.
9. Draw the V–I characteristics of UJT and mark the regions of importance.
10. Name the processes involved in the fabrication of ICs.
PART B — (5 ? 16 = 80 marks)
11. (i) Derive continuity equation. What are its uses? (10)
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(ii) Show that the resistivity of intrinsic germanium is 45 ? –cm at 300?K. If
a donor type impurity is added to the extent of 1 atom per 108 germanium
atoms, prove that the resistivity drops to 3.7 ? –cm. (6)
12. (a) (i) Explain about magnetic deflection in a 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 to 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)
Or
(b) (i) Describe about focusing system employed in CRT. (10)
(ii) A CRT has to the Y deflection plates a sinusoidal 5 Hz voltage of
35 V rms value. The observed deflection is a vertical line 0.045 m
long.
(1) Calculate deflection sensitivity
(2) If the acceleration voltage on this tube were increased to
double value, what would be the observed deflection for the
above voltage? (6)
13. (a) (i) Explain basewidth modulation with the aid of potential and
minority concentration throughout the base region. (10)
(ii) In a silicon transistor circuit, collector is given to a 10 V supply
through a 3 K ? resistance and the base is given to +5 V DC supply
through a 190 K? resistance. The emitter and negative terminals
of the supplies are connected together. The transistor with ? ? 90
is having CO I equal to 25 nA. Determine the region in which the
above transistor is working. (6)
Or
(b) (i) Draw the volt ampere characteristics of a JFET and explain about
each of the regions of operations of the same with relevant
equations. (10)
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(ii) An ideal germanium diode at room temperature has a static
resistance of 4.57 ? at a point where I = 45.6 mA. Find the
dynamic resistance at a feedback of 0.2 V. (6)
14. (a) Describe the operation of depletion type MOSFET.
Or
(b) With relevant diagrams, explain about Schottky barrier diodes.
15. (a) What is a MOS capacitor? Explain. How is it useful in charge transfer
devices?
Or
(b) What is a bilateral diode switch? Explain
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