**MODEL PAPER**

**B.E. DEGREE EXAMINATION.**

**Second Semester**

**Electronics and Instrumentation Engineering**

**PH 137 — MATERIALS SCIENCE**

**(Common to Instrumentation and Control Engineering)**

Time : Three hours Maximum : 100 marks

Answer ALL questions.

PART A — (10 ´ 2 = 20 marks)

- Show that for a simple cubic lattice .
- Name the types of structure and sketch the unit cell of Copper and Chromium.
- The Fermi energy of sodium is 3.2 eV. Calculate the Fermi wave vector.
- Explain Meissner effect.
- Give two examples of an intrinsic semiconductor.
- How the magnetic materials are classified on the basis of their spin?
- Differentiate between direct and indirect band gap.
- What are the different polarisation mechanisms in dielectric?
- What are excitons?
- What are the different phosphors used in CRO screens?

PART B — (5 ´ 16 = 80 marks)

- What is super conductivity? Mention the important property changes that occur in materials when they change from normal to super conducting state. Explain Type I and Type II super conductor. Discuss two applications. The critical temperature for Hg with isotopic mass 199.5 is 4.185 K. Calculate the critical temperature when its mass changes to 203.4.
- (a) Define packing fraction. Prove that the close packing of atoms in hcp structure demands an ratio c/a = 1.633.

** ** Show that the atomic packing fraction for fcc and hcp metals are the same. What is meant by crystal imperfections?

Or

** **(b) On the basis of free electron theory derive an expression for the electrical conductivity. What are the main sources of electrical resistance in metals? Discuss the effect of impurity and temperature on the conductivity.

- (a) Distinguish between intrinsic and extrinsic semiconductor. Obtain an expression for the carrier concentration for an extrinsic semiconductor.

Or

** **(b) What is Hall effect? Show that for a *p*–type semiconductor the Hall coefficient R_{H} is given by R_{H} = 1/pe.

** ** Describe an experimental set up for the measurement of the Hall voltage.

- (a) Draw a B–H curve for a ferromagnetic material. Identify retentivity and coercive field on the curve. What is the energy loss per cycle? What are ferrites? Mention their applications.

Or

** **(b) Explain internal field in a solid dielectric and obtain an expression for crystals possessing cubic symmetry. Obtain Clausius Mosotti equation. What is dielectric loss?

- (a) What are colour centres? What are the different types? Explain F and V centres. What is photoconductivity?

** ** Calculate the number of photons from the green light of mercury required to do one joule of work.

Or

** **(b) Explain the theory and working of LCD. Explain the advantages of using LCD.

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