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?
(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)
(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)