B.E./B.Tech.Degree Examinations, November/December 2010

Regulations 2008

Second Semester

Common to all branches

PH2161 Engineering Physics II

Time: Three Hours Maximum: 100 Marks

Answer ALL Questions

Part A - (10 x 2 = 20 Marks)

1. De¯ne electrical conductivity. What i s its unit?2. De¯ne Fermi level.

3. The intrinsic carrier density at room temperature in Ge i s 2:37 £ 1019/m3. If the

electron and hole mobilities are 0.38 and 0.18 m2/v/s respectively, calculate the

resistivity.

4. Given an extrinsic semiconductor, how will you ¯nd whether it i s n-type or p-type.

5. What are `coercivity' and `retentivity' of magnetic materials?

6. What is isotope e®ect in superconductivity?

7. Calculate the electronic polarisability of Neon. The radius of Neon atom is 0.158

nm. Take "0 = 8:854 £ 10¡12 Fm¡1.

8. Distinguish between dielectric loss and dielectric breakdown.

9. What i s the basic principle of `solid-state amorphization' method of producing

metallic glass?

10. Write any two properties of carbon nano tubes.

Part B - (5 x 16 = 80 Marks)

11. (a) (i) Deduce expression for electrical conductivity and thermal conductivity ofa conductor and hence obtain Wiedemann-Franz law. (5 + 5 + 3)

(ii) The thermal conductivity of metal i s 123.92 W/m/K. Find the electrical

conductivity and Lorentz number, when the metal has relaxation time

10¡14 sec at 300 K. Density of electrons = 6 £ 1028 m¡3. (3)

OR

11. (b) (i) Derive an expression for electrical conductivity based on Quantum theory.

(8)

(ii) Write the expression for Fermi distribution function and explain with suit-

able diagram. How does it vary with temperature? (4)

(iii) Calculate the Fermi energy and Fermi temperature in a metal. The Fermi

velocity of electrons in the metal is 0:86 £ 106 m/s. (4)

12. (a) (i) Obtain an expression for the carrier concentration of electrons in an in-

trinsic semiconductor. (10)

(ii) Starting with the conductivity of charge carriers in an intrinsic semicon-

ductor, describe how will you determine the bandgap of an intrinsic semi-

conductor. (6)

OR

12. (b) (i) How does the carrier concentration vary with temperature in an extrinsic

semiconductor? Explain. (6)

(ii) Derive an expression for Hall coe±cient of an n-type semiconductor. (6)

(iii) The Hall coe±cient of a specimen of a doped silicon is found to be 3:66£ 10¡4 m¡3/C. The resistivity of the specimen is 8:93 £ 10¡3 m. Find the

mobility and density of the charge carriers. (4)

13. (a) (i) State the origin of magnetic moment. (4)

(ii) How are magnetic materials classi¯ed based on magnetic moments? Com-

pare their properties (susceptibility, temperature dependence). Give also

their characteristics and examples. (2 + 10)

OR

13. (b) (i) What i s Meissner e®ect? Prove that all the superconductors are perfect

diamagnets in the superconducting state. (2 + 2)

(ii) Brie°y explain the following :

(1) SQUID (4)

(2) BCS theory (4)

(3) High Temperature Super Conductors (4)

2 64017

132 132 132

14. (a) (i) De¯ne the following:

(1) Dielectric constant, "r

(2) Polarizability, ®

(3) Polarization vector, ¡!P

(4) Electric °ux density, D

(5) Electric susceptibility, Â

Give also the necessary equations relating the above quantities. (12)

(ii) Calculate the electronic polarizability of an argon atom whose "r = 1:0024

at NTP and N = 2:7 £ 1025 atoms=m3. (4)

OR

14. (b) (i) What are the factors which in°uence the dielectric loss in a material? (4)

(ii) What are the di®erent types of dielectric materials used in capacitors?

What will be the resulting characteristics? (6)

(iii) What i s the role of dielectric materials in electric transformers? Explain.

(6)

15. (a) (i) What are shape memory alloys? Describe the characteristics of shape

memory alloys. (8)

(ii) List out any four applications of shape memory alloys. (4)

(iii) Mention any two advantages and two disadvantages of SMAs. (4)

OR

15. (b) (i) How do nanomaterials di®er from bulk materials? Explain the preparation

of nanomaterials by Chemical Vapour Deposition method and give their

important properties. (2 + 6 + 3)

(ii) Explain how the carbon nanotubes are fabricated using arc method. (5)

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