Anna University Chennai 2005 B.E Electronic Instrumentation & Control Engineer /B.TECH:Material science - exam paper

B.E/B.TECH.DEGREE exam ,APRIL/MAY 2005
Second semester,E I
Material science


Time taken : 3Hrs
Maximum marks : 100


PART A (10 x two =20)

1. find packing factor for f.cc. strucuture.

2. compute the largest wavelength of X rays that can be analysed by a crystal with a grating constant = 3.05 armstrong

3."Type I superconductor are perfect diamagnets".Justify this statement with proper reasoning.

4. Aluminium is alloyed with better conducting material like copper.Will the conductivity of alloy increase or decrease?Give cause for your ans

5.Carrier concentration of an intrensic semi-conductor increases with an increase in temperature.explain how this happens physically.

6.Name 1 compound semiconductor and mention its application.Justify its use for that apllicatio.

7.The dielectric constants of solids are ,in general ,higher than those of gases.Explain

8. elaborate ferrites?In what way they are superior to ferromagnetic materials?Give cause.

9.Distinguish ranging from phosphorescence and fluorescence.Name 1 material for every kind.

10 elaborate excitons?How do they change absorption spectra?

PART B ( five X 16 =80)

11(i) Write notes on trap levels and colour centres.

(ii) What is photoconductivity? provide a physical explanation for photoconductivity in semiconductors.

12 (a) (i) discuss the physical concepts involved in quantised free electron theory of metals and also the chnages in its predictions on electricla conductivity from those based on classical theory.

(ii)Discuss the insulator behavior of diamond on the consideration of energy bands

OR

(b) (i) elaborate kind II superconductors?Discuss the various parts of their magnetisation curve from the viewpoint of magnetic induction.Also,comment on their resistivity in these regeions

(ii) discuss D.C and A.C josephson effects

13 (a) (i)Derive expressions for carrier concentration and conductivity of an n-type semiconductor both at low and at high temperatures

(ii) obtain the resistance of an intrinsic Ge rod of one cm ,long one mm wide and one mm thick at 300 K when current is passing through lengthwise direction.Given ni = 2.5 X 10 ^19 /m ^3 ; ? e = 0.39 m ^2 V -s; ?h = 0.19 m ^2 /v -s at 300 K.Assume e = 1.6 X 10 ^-19 C

OR

(b) (i) Write notes on compound semiconductors

(ii)Hall effect can be applied to the construction of a gaussmeter.Explain

(iii) An elctrical filed of 100 V/m is applied to a semiconductor whose hall coefficient is 0.0125 m ^ three /c.Dtermine the current density in the sample assuming Meow =0.36 m^2/V -s and e =1.6 X 10 ^-19C

14 (a) (i)Derive Blausius -Mosotti relation

(ii)Assuming the genral expressions for dielectric polorisation ,obtain the realtion connecting the dielctric constant and polarisability = two X 10 ^ -40 F-m^2.Assuming that the internal field is provided by lorentz formula ,calculate the ratio of internal field to applied field.Also ,find the value of Er.(Assume E 0 = 8.8 X 10 ^-12 F/m

OR

(b) (i) provide the important features of ferromagnetism.

(ii) discuss domain theory of ferromagnetism.Account for the observed hysterisis curve on the baisi of theory.

15 (a) (i) Derive Bragg's legal regulations

(ii) Descirbe the poeder crystal method of X ray diffraction and discuss how it can be used for deducing crystal structure

OR

(b) explain all kinds of imperfections in crystals.

Earning:   Approval pending.