# 2004 Anna University Chennai B E Electronics Tele Communication Engineering EC 141 ELECTRONIC DEVICES Question paper

** University Question Papers **

**
**2004 Anna University Chennai B E Electronics Tele Communication Engineering EC 141 ELECTRONIC DEVICES Question paper

BE/B.TECH EXAMINATION,NOVEMBER/DECEMBER 2004

Second Semestor

Electronics and Communication Engineering

EC 141-ELECTRONIC DEVICES

(Common to Biomedical Engineering)

Time:3 hrs Maximum:100marks

Answer ALL questions

PART A-(10X2=20 marks)

1.Calculate the time taken by an electron which has been accelerated through a potential difference of 1000V to

traverse a distance of 2cm.Given q=1.6X10^-19 and m=.9.1X10^-31kg.

2.State two applications of magnetic deflection.

3.Write down the expression for drift current density due to electrons.

4.Draw the resistance-temperature characteristics of thermistor and comment on it.

5.Define tunneling phenomenon.

6.Calculate the values of Ic and Ie for a transistor alpha(dc)=0.97 and Icbo=10uA and Ib is measured as 50uA.

7.Depletion MOSFET is commonly known as “Normally-ON-MOSFET”why?

8.What are all internal capacitance in MOSFET?

9.What is “interbase resistance “ of UJT?

10.What is ion implantation process?

PART B-(5X16=80 marks)

11.(i)The electron bean in a CRT is displayed vertically by a magnetic field of flux density 2X10^-4wb/m2 The length

of the magnetic field along the tube axis is the same as that of the electrostatic deflection plates.The final anode

voltage is 800V.Derive and calculate the voltage which should be applied to the Y-deflection plates 1cm apart,

to return the spot back to the centre of the screen.(10)

(ii)Describe with neat diagram the principle of operation of Dynamic scattering type LCD.(6)

12.(a)Derive the continuity equation from the first principle and also derive 3 special cases of continuity equation.(16)

Or

(b)(i)Derive the Ebers-Moll model for a PNP transistor and give equation for Ie and Ic.(8)

(ii)The diode current is 0.6mA when the applied voltage is 400mV and 20mA when the applied voltage is 500mV.

Determine n (eta) .Assume kT/a=25mA.(8)

13.(a)Explain Hill effect.How can Hll effect be used to determine some of the properties of a semiconductor and

also discuss it's applications.(16)

Or

(b)Describe with the help of a relevant diagram,the construction of a LED and explain it's working.(16)

14.(a)With the help of suitable diagram explain the working of different types of MOSFET.(16)

Or

(b)(i)Draw and explain the energy band diagram for conductors,insulators and semiconductors.(4)

(ii)Sketch the energy band diagram for P-N junction under open circuit condition and obtain the expression for

contact difference of potential Eo.(12)

15.(a)(i)With volt-ampere characteristics describe the working principle of an SCR.Also explain it's construction details.(14)

(ii)Draw the two transistor model of an SCR.(2)

Or

(b)With necessary diagrams explain the fabrication process of NMUS devices.(16)