2005 Anna University E&I - Material Science Question paper

[ganeshbala]

B.E/B.TECH.DEGREE EXAMINATION ,APRIL/MAY 2005

Second semester,E I

[blink]Material science[/blink]


Time taken : 3Hrs
Maximum marks : 100


PART A (10 x 2 =20)

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

2. Calculate 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 reason for your answer

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

6.Name one 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. What are ferrites?In what way they are superior to ferromagnetic materials?Give reason.

9.Distinguish between phosphorescence and fluorescence.Name one material for each type.

10 What are excitons?How do they change absorption spectra?

PART B ( 5 X 16 =80)

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

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

12 (a) (i) Explain 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) What are type II superconductors?Discuss the different parts of their magnetisation curve from the viewpoint of magnetic induction.Also,comment on their resistivity in these regeions

(ii) Explain 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) Find the resistance of an intrinsic Ge rod of 1 cm ,long 1 mm wide and 1 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 ^ 3 /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 = 2 X 10 ^ -40 F-m^2.Assuming that the internal field is given 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) Give the important features of ferromagnetism.

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

15 (a) (i) Derive Bragg's law

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

OR

(b) Discuss all types of imperfections in crystals.