Anna University Chennai 2005 B.E Electronic Instrumentation & Control Engineer /B.TECH:Electron Devices - Question Paper

B.E/B.TECH.DEGREE exam , NOV/DEC 2005
Second semester,E I
Electron Devices


Time taken : 3Hrs
Maximum marks : 100


PART A (10 x two =20)


1.What is deflecting defocusing?

2.What assumptions are made while analyzing the motion of an electron in an electric field?

3.The reverse saturation current of a silicon PN junction diode is 10?A .Calculate the diode current for the forward bias cottage of 0.6v at 25 degrees.

4.Why Schottky diode is switch off faster than bipolar diode?

5.Define the generalized hybrid parameters for a transistor .

6.Why are power transistors given with heat skins?

7.Find the Transconductance when the reverse gate voltage of JFET modifications form 4.0 to 3.9v, and the drain current charges from 1.3 to 1.6MA.Find the value of transconductance.

8.Define Latching current and holding current for a thyrister.

9.What are liquid crystal materials commomnly used?

10.What is the effect of light on semi conductors?


PART B (5 X 16 =80)

11.(i) discuss why an electron takes a cycloid path when it is exposed to perpendicular electrical and magnetic fields.

(ii)A charged particle having charge thrice that of an electron and mass twice as that of an electon is accelerated through a potential difference of 50v before it enters a uniform magnetic field of flux density of 0.02 Wb/m two at an angle of 25 degrees with the field.Find the

(1) Velocity of an charged particle before entering the field

(2) Radius of the helical path and

(3)Tinc of 1 revolution


12 (a) define the phenomenon of diffusion of cahrge carriers in semiconductors.

A sample of silicon at a temperature T is intrinsic condiction has a resistivity of
25 X 10 14 ohm -cm.The sample is now doped to the extent of four X 10 10 donor
atoms/cm three and the 10 10 acceptor atoms/cm 3.Find the total conduction current density if an electric field of four v/cm is applied across the sample.Given that ?n= 1250 cm 2/v-s ,?P =475 cm2/v-s at the provided comperature

OR

(b) Derive the diode current formula relating the voltage V and current I provided as
I=Io V/[e3vT-1] from 1st principles.The diode current is 0.6 mA when the applied voltage is 400v and 20 mA when the applied voltage is 500 mv.Determine whether the diode is made of silicon or germanium.Assume Room temperature.

13 (a) Compare he performance of a transistor in various configurations ,and raw the Ebers -Moll model for a PNP transistor and provide the formula for emitter current and collector current

OR

(b) Draw and discuss the 100 frequency and high frequency response of transistor .Discuss the effect of the coupling capacitance on the low frequency response.


14 (a) discuss how the transconductance of a JFET varies with drain current and gate voltage.

OR

(b) Draw the circuit of UJT and discuss its operation with the help of emitter characteristics.Draw the equivalent circuit.

15(a) elaborate the various change transfer devices?(CTD).Draw neat sketches and discuss the operator ,also listing their application.

OR

(b) How does an LED differ from an ordinary PN junction diode?Draw and discuss the 7 segment LED display.

Earning:   Approval pending.