DipIETE – ET (NEW SCHEME) – Code: DE54

Subject: ENGINEERING MATERIALS

Time: 3 Hours Max. Marks: 100

NOTE: There are 9 Questions in all.

· Question 1 is compulsory and carries 20 marks. Answer to Q.1 must be written in the space provided for it in the answer book supplied and nowhere else.

· Out of the remaining EIGHT Questions answer any FIVE Questions. Each question carries 16 marks.

· Any required data not explicitly given, may be suitably assumed and stated.

Q.1 Choose the correct or the best alternative in the following: (210)

a. A material which can store electrical energy is

(A) Capacitor (B) Inductor

(C) Resistor (D) Dielectric material.

b. The main purpose of a capacitor is to

(A) block current flow (B) help current flow

(C) store energy (D) dissipate heat

c. Materials which provide path to the magnetic flux are classified as

(A) insulating materials (B) semiconducting materials

(C) magnetic materials (D) dielectric materials

d. A pure semiconductor under ordinary conditions behave like

(A) a conductor (B) an insulator

(C) magnetic materials (D) a ferroelectric material

e. Which of the following materials have maximum magnetic permeability?

(A) Pure iron (B) 4% silicon steel

(C) Grain oriented Si-Fe (D) Ni-Fe

f. The temperature at which a ferromagnetic material becomes a paramagnetic is called

(A) Curie temperature (B) Maximum temperature

(C) Minimum temperature (D) All the above

g. In photo emission of electrons the energies of electrons emitted depend on the

(A) intensity (B) wavelength

(C) velocity of light (D) frequency

h. The Fermi level is

(A) an average value of all available energy levels

(B) the highest occupied energy level at 0º K

(C) an energy level at the top of the valence band

(D) the largest available energy level

i. In a p-n junction in equilibrium with zero bias

(A) no holes or electrons cross the junction

(B) only electrons cross the junction

(C) equal number of electrons and holes cross the junction

(D) only holes cross the junction

j. The Hall voltage across an impurity semiconductor crystal can be increased by

(A) increasing the concentration of impurity atoms in the crystal

(B) increasing the thickness of the crystal

(C) increasing the width of the crystal

(D) increasing the current flowing through the crystal

Answer any FIVE Questions out of EIGHT Questions.

Each question carries 16 marks.

Q.2 a. Explain the effect of temperature on electrical conductivity of metals. (8)

b. The resistivity of pure copper is 1.56 micro ohm cm. An alloy of copper containing one atomic percent of nickel has a resistivity of 2.81 micro ohm cm. An alloy of copper containing three atomic percent silver has a resistivity of 1.98 micro ohm cm. What is the resistivity of an alloy containing two atomic percent nickel and two atomic percent of silver? (8)

Q.3 a. Explain, the phenomenon of polarisation. (8)

b. Derive Clausius-Mossotti relation for dielectric constant Î_r and Polarisability a. (8)

Q.4 a. Explain the dielectric properties of polymeric system. (8)

b. Write a note on ferroelectricity and piezoelectricity. (8)

Q.5 a. Explain the phenomenon of Magnetostriction. (8)

b. Write a note on Silicon iron and Nickel iron alloy. (8)

Q.6 a. Derive the relation between diffusion constant and mobility. (8)

b. Explain device potting, susceptor materials, reactors envelopes, plastic and pump fluids. (8)

Q.7 a. Explain zener breakdown and avalanche breakdown. (8)

b. What are the different types of resistors? Explain metal oxide film resistors. (8)

Q.8 a. Explain the two transistor analogue of an SCR. (8)

b. What are relays? Explain thermal type of relay. (8)

Q.9 a. Explain zone refining technique used for the purification of semiconductors. (8)

b. Draw and explain the drain and transfer characteristics of JFET. (8)