# 2005 Anna University Chennai B E Electronics Tele Communication Engineering EC 1202 ELECTRON DEVICES Question paper

** University Question Papers **

**
**2005 Anna University Chennai B E Electronics Tele Communication Engineering EC 1202 ELECTRON DEVICES Question paper

BE/B.TECH DEGREE EXAMINATION,NOVEMBER/DECEMBER 2005

Third Semester

Electronics and Communication Engineering

EC 1202-ELECTRON DEVICES

(Regulations 2004)

Time: 3hrs Maximum:100marks

Answer ALL questions.

PART A-(10X2=20 marks)

1.What are the factors on which the electrostatic deflection sensitivity of a CRO depends?

2.What is mass action law?

3.What is the Fermi level in (a)in N type material and (b)a P type material?

4.A silicon diode has a saturation current of 7.5uA at room temperature.Calculate the saturation current at 400K.

5.What happens to the capacitance of a varactor diode when the reverse bias voltage across it is increased?Mention two applications of varactor diode.

6.What is the wavelength of (a)ultra violet and (b)infrared?

7.Derive the expression for common emitter current gain in terms of common base one.

8.What is early effect?By what other name, it is known?

9.When is metal semiconductor contact preferred?Mention a familiar device having this type of contact.

10.Define intrinsic stand off ratio of an UJT.What is its range?

PART B-(5X16=80 marks)

11.(i)How is drain current related to gate to source voltage and drain to source voltage in a JFET?(8)

(ii)Compate BJT and FET.(8)

12.(a)(i)Describe the motion of electron in a magnetic field(4)

(ii)Prove that the time taken by electron for one revolution is 2*pi/x/w, where w is the angular velocity of the

electron.(6)

(iii)Two plane parallel plates are placed 8mm apart and applied a voltage of 300V.An electron travels from the plate

of lower potential to the higher potential one with an initial velocity of 10^6m/s.Calculate the time taken by the

electron to reach the other plate.The charge of electron is 1.6*10^-19C and its mass is 9.1*10^-31kg.(6)

Or

(b)What is Fermi-Dirac distribution function?What is its significance?Draw this function applied to (i)intrinsic material

(ii)n type material and (iii)p type material and explain.(16)

13.(a)Discuss the electron and hole concentrations at thermal equilibrium with the help of schematic band diagram and

carrier concentrations for (i)intrinsic (ii)p type and (iii)n type semiconductors.(16)

Or

(b)(i)What is hall effect?Discuss its applications.(8)

(ii)Write about drift current and diffusion current.(8)

14.(a)What is tunnel diode?Explain its operation with the help of band diagrams and I-V characteristics for various

biasing conditions.(16)

Or

(b)(i)Discuss the switching characteristics of a junction diode for a pulse input.(10)

(ii)Write notes on photo diode and its characteristics.(6)

15.(a)Draw the basic structure and circuite symbol of an SCR.Draw the characteristic curve of this device and explain

for its nature.Derive the equation for the anode current and mention its significance.(16)

Or

(b)(i)Write detailed note on:(1)rectifying contact and (2)ohmic contact.(8)

(ii)Mention the applications of triac and diac.(8)