PH 2161 Engineering Physics 2 Nov/Dec 2010

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. Defne electrical conductivity. What i s its unit?
2. Defne 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 of
a 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)

PH 2161 Engineering Physics 2 Nov/Dec 2009

B.E./B.Tech. DEGREE EXAMINATION, NOVEMBER/DECEMBER 2009

Second Semester

Civil Engineering

PH 2161 — ENGINEERING PHYSICS — II

(Regulation 2008)

(Common to all branches)

Time : Three hours Maximum : 100 Marks

Answer ALL Questions

PART A — (10 × 2 = 20 Marks)

1. Find the drift velocity of the copper wire whose cross sectional area is 1 mm2
when the wire carries a current of 10 A. Assume that each copper atom
contributes one electron to the electron gas. Given 3 28 m 10 8.5 n × = .
2. State Wiedemann-Franz Law.
3. Define Hall effect and Hall voltage.
4. What is the difference between n-type and p-type semiconductor?
5. What do you mean by energy product?
6. What is domain theory of ferromagnetism?
7. Define ionic and orientation polarization.
8. What is discharge breakdown?
9. What are shape memory alloys? Give examples.
10. Explain the importance of mechanical properties of nano phase materials.

PART B — (5 × 16 = 80 Marks)

11. (a) (i) Explain Fermi-Dirac distribution function and how it varies with
temperature. (8)
(ii) Derive an expression for the density of states and based on that
calculate the carrier concentration in metals. (8)


Or
(b) Discuss classical free electron theory of metals. Obtain the expression for
electric resistivity in terms of well known microscopic quantities. Discuss
its dependence on temperature. (16)
12. (a) Obtain an expression for density of electrons in the conduction band of an
n-type and density of holes in the valence band of an p-type intrinsic
semiconductor. (16)
Or
(b) (i) Explain Hall effect in p-type and n-type semiconductors. (6)
(ii) Derive an expression of Hall coefficient. (4)
(iii) Describe the experimental setup for the measurement of Hall
coefficient. (6)
13. (a) (i) Explain hysteresis on the basis of domain theory of ferromagnetism.
(8)
(ii) Distinguish between soft and hard magnetic materials. (8)
Or
(b) (i) Explain in detail high C T , superconductors with examples. (6)
(ii) Write a note on isotope effect. Describe type I and type II
superconductors with suitable diagrams. (10)
14. (a) (i) Briefly explain the effects of frequency and temperature on
polarization of dielectrics. (10)
(ii) Deduce the Clausius-Mosotti relation. (6)
Or
(b) (i) Explain ferroelectric materials and their properties. (10)
(ii) Write any five applications of ferroelectric materials. (6)
15. (a) (i) Discuss the applications of nanomaterials in various fields. (6)
(ii) Discuss any two techniques of synthesis of carbon nanotubes and
mention its properties. (10)
Or
(b) Give a detailed account on metallic glasses, their method of production,
types, properties and applications. (16)

PH 2161 Engineering Physics 2 Nov/Dec 2011

B.E./B.Tech. DEGREE EXAMINATION, NOVEMBER/DECEMBER 2011.

Common to All B.E./B.Tech.

Second Semester

182202 — ENGINEERING PHYSICS – II

(Regulation 2010)

Time : Three hours Maximum : 100 marks

Answer ALL questions.

PART A — (10 ´ 2 = 20 marks)

1. A wire has a resistivity of 1.54 ´ 10–8 ohm-m at room temperature. There are
5.8 ´ 1028 electrons per m3. Calculate the relaxation time.
2. Define fermi energy.
3. Find the resistance at 300K of an intrinsic Ge rod which is 1 cm long, 1 cm wide and 1 cm thick. The intrinsic carrier density at 300K is 2.5 ´ 1019 m–3 and the mobilities of electron and hole are 0.39 and 0.19 m2 V–1 s–1 respectively.
4. State the Hall effect.
5. Give any two properties of hard magnetic materials.
6. What are the properties of superconductors?
7. How does temperature affect electronic and ionic polarizations?
8. An elemental dielectric material has a relative dielectric constant of 12. It contains 28 10 5 ´ atoms /m3. What is its electronic polarizability if Lorentz field is assumed.
9. Mention any two applications of metallic glasses.
10. What are shape memory alloys?

PART B — (5 ´ 16 = 80 marks)

11. (a) (i) State the postulates of classical free electron theory of metals. (8)
(ii) Obtain the expressions for electrical and thermal conductivities and hence prove Wiedemann-Franz law. (8)

Or

(b) (i) Explain Fermi distribution function. (4)
(ii) Obtain an expression for the Fermi energy at T = 0K in a good conductor and hence the average energy of an electron. (12)
12. (a) (i) Obtain an expression for the intrinsic carrier concentration in an intrinsic semiconductor. (12)
(ii) Show that the Fermi level is exactly at the middle of the forbidden energy gap of an intrinsic semiconductor at T = 0K. (4)

Or

(b) (i) Obtain an expression for the carrier concentration in a n – type semiconductor. (12)
(ii) How conductivity varies with temperature in an n-type extrinsic semiconductor? (4)
13. (a) Describe the ferromagnetic domain theory in detail. How does it account for hysteresis phenomenon? (16)
Or
(b) (i) Distinguish between Type I and Type II superconductors. (8)
(ii) Explain the Meissner effect. (4)
(iii) State and explain any two applications of super conductors. (4)
14. (a) (i) Obtain an expression for the internal field inside the dielectric. (12)
(ii) Deduce Claussius – Mosotti equation from local field expression for a dielectric having contribution due to electrical polarizability alone. (4)

Or

(b) Write a note on :
(i) Space charge polarisation. (8)
(ii) Dielectric break down. (8)


15. (a) (i) What are nanomaterials? Describe any two methods of production of nanomaterials. (8)
(ii) Discuss atleast two important applications of nanomaterials. (8)

Or

(b) Write a note on :
(i) Shape memory alloys. (8)
(ii) Carbon nanotubes. (8)

PH 2161 Engineering Physics 2 May/June 2009

B.E./B.Tech. DEGREE EXAMINATION, MAY/JUNE 2009.

Second Semester

Civil Engineering

PH 2161 — ENGINEERING PHYSICS — II

(Common to all branches of B.E./B.Tech.)

(Regulation 2008)

Time : Three hours Maximum : 100 marks

Answer ALL questions.

PART A — (10 × 2 = 20 marks)

1. Define the terms
(a) relaxation time and
(b) mobility.
2. What are the main drawbacks of classical free electron theory of metals?
3. What is meant by Fermi energy? What is physical significance?
4. What is meant by Hall effect? Write an expression for the Hall coefficient.
5. Distinguish between intrinsic and extrinsic semiconductors.
6. What do you understand by the terms “ critical temperature “and “ critical
field” of a superconductor?
7. Distinguish between soft and hard magnets.
8. Mention four types of polarization mechanisms that can take place in the
presence of an electric field in dielectric materials.
9. What are shape memory alloys ? What are their properties?
10. What are the applications of carbon nanotubes?

PART B — (5 × 16 = 80 marks)

11. (a) (i) State the assumption of the classical free electron model. (4)
(ii) Obtain an expression for the electrical conductivity of a metal on
the basis of classical free electron theory. (8)
(iii) The mobility of electron in copper is 3 × 10–3 m2/Vs. Assuming
e = 1.6 × 10–19 C and me = 9.1 × 10–31 kg, calculate the mean free
time. (4)
Or
(b) (i) Explain the meaning of ‘density of states’. Derive an expression for
the number of allowed states per unit volume of a solid. (8)
(ii) Write an expression for the Fermi energy distribution function,
( ) E fFD and discuss its behaviour with change in temperature. Plot
( ) E fFD versus E for T = 0 K, and T > 0 K. (8)
12. (a) (i) Describe the energy band theory of solids with the help of neat band
diagrams. Distinguish between metals, insulators and
semiconductors on the basis of band theory. (8)
(ii) Derive an expression for the charge density in terms of Hall voltage
and further explain how the mobility of the charge carriers can be
evaluated by knowing the conductivity. (8)
Or
(b) (i) Derive an expression for the electrical conductivity of an intrinsic
semiconductor. (8)
(ii) The electron mobility and hole mobility in silicon are 0.135 m2/V.s
and 0.048 m2/V.s respectively at room temperature. If the carrier
concentration is 1.5 × 1016 m–3, calculate the resistivity of silicon at
room temperature. (4)
(iii) A sample of silicon doped with 1023 phosphorous atoms/m3. Find the
Hall voltage in a sample with thickness = 100 m µ , current,
Ix = 1mA and magnetic field, Bz = 0.1 Wb/m2. (Assume electron
mobility, e µ = 0.07 m2/V.s) (4)
13. (a) (i) Distinguish between Type I and Type 11 superconductors. (4)
(ii) What are Cooper pairs? Give an outline of BCS theory of
superconductivity. (8)
(iii) Write a short note on SQUIDs. (4)
Or
(b) (i) Give the classification of magnetic materials on the basis of
magnetic susceptibility. Briefly discuss the domain theory of
ferromagnetism. (8)
(ii) Calculate the energy loss per hour in the iron core of a transformer,
if the area of the B-H loop is 250 J/m3 and the frequency of the
alternating current is 50 Hz. The density of the iron core is
7.5 ×103 kg/m3 and mass of the core is 10 kg. (4)
(iii) A magnetic field of 2000 A/m is applied to a material which has a
susceptibility of 1000. Calculate the
(1) intensity of magnetization and
(2) flux density. (4)
14. (a) (i) Derive an expression for the internal field in a dielectric solids
material. (8)
(ii) The dielectric constant of a helium gas at NTP is 1.0000684.
Ca1culate the electronic polarizability of He atoms if the gas
contains 2.7 × 1025 atoms /m3 and hence evaluate the radius of the
helium atom. ( 0 ε = 8.85 × 10–12 F/m). (4)
(iii) Calculate the polalization produced in a dielectric medium of
dielectric constant 6 when it is subjected to an electric field of
100 V/m. ( 0 ε = 8.85 × 10–12 F/m). (4)
Or
(b) (i) What is ferroelectricity? Explain the hysteresis curve exhibited by a
ferroelectric material with a suitable sketch. Give examples for
ferroelectric materials. (8)
(ii) A capacitor consists of two conducting plates of area 200 cm2 each
separated by a dielectric constant, ε = 3.7 of thickness 1 mm. Find
the capacitance and the electric flux density when a potential of
300 V is applied. ( 0 ε = 8.854 × 10–12 F/m). (4)
(iii) Write a short note on uses of dielectric materials. (4)
15. (a) (i) What are nanotubes ? Describe their synthesis and properties. (8)
(ii) Write a short note on pulsed laser deposition. (8)
Or
(b) (i) Describe the preparation and properties of metallic glasses. (8)
(ii) Write short notes on nanoparticles and their applications. (8)