ANNA UNIVERSITY PART - A '2' Marks Q&A

1. What is a space lattice? (A.U. May 2008, Dec 2009)

It is an array of points in three dimensions in which every point has an identical
surrounding.

2. What is a unit cell? (A.U. May 2011, Jan 2009)

It is the smallest volume of a solid from which the entire crystal structure can be
constructed by repetition in three-dimension.

3. Name the seven crystal systems. (A.U. Jan 2010)

(i) Cubic (ii) Tetragonal (iii) Orthorhombic (iv) Monoclinic (v) Triclinic (vi)
Rhombohedral
(vii) Hexagonal

4. What is a primitive cell? (A.U. May 2011)

A primitive cell is the simplest type of unit cell which contains only one lattice
point per unit cell.

5. Name the crystal structure of the following: (a) Gold (b) Germanium (c)
Barium (d) Zinc
(A.U. Dec 2008)
(a) Gold - FCC (b) Germanium - Diamond cubic (c) Barium - BCC (d) Zinc – HCP

6. Bismuth has a = b = c = 4.74 Å and angles α = β = γ = 60°. What is its crystal

structure?
(A.U. Nov 2008)
Given a = b = c = 4.74 Å, α = β = γ = 60°
Since a = b = c and α = β = γ ≠ 90°
The crystal structure of Bismuth is trigonal (Rhombohcdral)

7. What are Bravais lattices? od (A.U. May 2010, Jan 2012)

There are only 14 ways of arranging points in 3 - dimensional space such that the
environment looks same from (010 D each point. ie., there are 14 possible types of
space lattices out dub of the seven crystal systems. These 14 space lattices are
called Bravais lattices.
8. Give the values of number of atoms in unit cell for SC, BCC, FCC. (A.U. Jan
2008, 2009)

9. Define coordination number. (A.U. Dec 2010)

It is the number of nearest neighbouring atoms that any atom has in the given
crystal structure.

10. Give the coordination numbers for SC, BCC, FCC, HCP and Diamond (A.U.
May 2009)

11. Define atomic radius. (A.U. Jan 2011)

The half of the distance between nearest neighbouring atoms in a crystal is known
as atomic radius. The atomic radius is denoted by 'r' and it is usually expressed in
terms of the cube edge 'a' (lattice parameter).

12. Obtain the formula for atomic radius 'r' in terms of (e lattice constant 'a' for
simple cubic.
(A.U. Dec 2009)
In simple cubic structure,
2r = a
r = a/2

Face of the SC unit cell

13. Arrive an expression for atomic radius in terms of lattice constant for BCC.
(A.U. May 2012)
In BCC, along the body diagonal AG,
r + 2r + r = a√3
4r = a √3
r = √3 a / 4

14. Derive an expression for atomic radius in terms of lattice parameter for FCC.
(A.U. Jan 2011)
For FCC, along any face diagonal,
r + 2r + r = a √2
4r = a √2
r = a√2 / 4
15. Define packing factor. What is its unit? (A.U. April 2011, May 2012, May
2013)
It is the ratio of volume of atoms in unit cell to the volume of the unit cell. It has no
unit, since it is a ratio of same physical quantity.

16. Calculate packing factor in the case of simple cubic structure. (A.U. Dec
2012)
Packing factor = Volume occupied by the atoms in a unit cell (v) / Volume of unit
cell (V)

17. Calculate packing factor of body centred cubic crystal. (A.U. May 2013)
Packing factor = Volume occupied by the atoms in a unit cell / Volume of the unit
cell
Number of atoms per unit cell = 2
For BCC, Atomic radius r = √3 a / 4

18. Calculate the packing factor of face centred cubic crystal. (A.U. May 2012)
Packing factor = Volume occupied by the atoms in a unit cell / Volume of unit cell
Number of atoms per unit cell = 4
19. What are Miller indice? (A.U. May 2010, Jan 2011)
A set of three numbers to designate a plane in a crystal is known as Miller indice of
the concerned plane, symbolised by (h k l)
The reciprocal of the intercepts made by the plane on the cryptallographic axes
which are reduced to smallest integers.

20. Give the expression for interplanar spacing for a cubic system interms of
lattice constant and Miller indices. (A.U. Jan 2012)

Interplanar spacing d =
a - lattice constant
h, k, l Miller indice

21. Sketch the (101) plane in a cubic system. (A.U. May 2008, Jan 2009)
22. Sketch (111) plane for a cubic crystal. (A.U. May 2010, Jan 2011)

23. Obtain Miller indices of a plane whose intercepts are a, b/2, 3c in a simple
cubic unit cell.
(A.U. Jan 2010)
Actual intercepts are a, b/2, 3c
Numerical parameters are 1, 1/2, 3
Reciprocals of the above 1, 2, 1/3
Miller indices of the plane is (3 6 1)

UNIT-II
1. On the basis of spin how the materials are classified as para, ferro, antiferro
and ferri magnetic. (A.U. May 2012)

i. Paramagnetic materials have few unpaired electron spins of equal magnitudes.

ii. Ferro magnetic materials have many unpaired electron spins with equal
magnitudes.
iii. Anti ferro magnetic materials have equal magnitude of spins but in antiparallel
manner.

iv. Ferrimagnetic materials have spins in antiparallel manner but with unequal
magnitudes.

2. What is Curie constant? or What is Curie law? (A.U. May 2008)

It is found that susceptibility (x) is inversely proportional to the temperature (T)

where C is constant and it is known as Curie constant. This relation is known as

Curie law.

3. State Curie Weiss law and its importance. (A.U. May 2010)

Curie - Weiss law is given by

where C→ Curie constants

T → Absolute temperature

θ → Curie temperature
Importance: It determines the susceptibility of the magnetic materials in terms of
temperatures ie., If the temperature is less than curie temperature, a paramagnetic
material becomes diamagnetic.

If the temperature is greater than Curie Temperature, a ferromagnetic material

becomes paramagnetic material.

4. What is ferromagnetism? (A.U. May 2010)

Certain materials like Iron (Fe), Cobalt (Co), Nickel (Ni) and certain alloys exhibit
spontaneous magnetization i.e., they have a small amount of magnetisation (atomic
moments are aligned) even in the absence of an external magnetic field.

This phenomenon is known as ferromagnetism.

5. What are ferromagnetic materials? (A.U. Jan 2008)

The materials which exhibit ferromagnetism are called as ferromagnetic materials.

6. What are the properties of ferromagnetic materials? (A.U. June 2011)

i. All the dipoles are aligned parallel to each other due to the magnetic interaction
between any two dipoles.

ii. They have permanent dipole moment. They attract the magnetic field strongly.

iii. They exhibit magnetisation even in the absence of magnetic field. This property
of ferromagnetic materials is called as spontaneous magnetisation.

7. What is saturation magnetisation?

The maximum magnetisation in a ferromagnet when all the atomic magnetic

moments are aligned is called saturation magnetization.
8. What is Giant magnetoresistance?

It is a quantum mechanical magnetoresistance effect observed in multilayers

composed of alternating ferromagnetic and non-magnetic conductive layers.

The effect is observed as a significant change in the electrical resistance depending

on whether the magnetization of adjacent ferromagnetic layers are in a parallel or
an antiparallel alignment. The overall resistance is relatively low for parallel
alignment and relatively high for antiparallel alignment.

The magnetization direction can be controlled, for example, by applying an

external magnetic field. The effect is based on the dependence of electron
scattering on the spin orientation.

9. Mention application of GMR.

The main application of GMR is magnetic field sensors, which are used to read
data in hard disk drives, biosensors, microelectromechanical systems (MEMS) and
other devices. GMR multilayer structures are also used in magnetoresistive
random-access memory (MRAM) as cell that store one bit of information.

ANNA UNIVERSITY SOLVED PROBLEMS

1. A magnetic field strength of 2× 10 5 amperes / metre is applied to a paramagnetic

material with a relative permeability of 1.01. Calculate the values of B and M
[A.U. May 2015]

Given data

Magnetic field strength H = 2 × 105 A/m

Relative permeability μr = 1.01

Solution

We know that

Substituting the given values, we have

2. Magnetic field intensity of a paramagnetic material is 10 4 ampere/metre. At

room temperature its susceptibility is 3.7 × 10 -3. Calculate the magnetization of the
material. [A.U. Dec 2014]

Given data

Magnetic field intensity H = 104 ampere / metre

Susceptibility χ = 3.7 x 10-3

Magnetization of the material = ?

Solution
We know that Magnetization = χ Η

Substituting the given values, we have

= 3.7 × 10-3 × 104

M = 37 ampere / metre

UNIT-III

1. What are elemental semiconductors? Give some important elemental

semiconductors. (A.U Dec 2014)

Elemental semiconductors are made from single element of the fourth group
elements of the periodic table.

Example : Germanium and silicon.

2. What are the properties of semiconductors? (A.U. June 2013)

i. They are formed by covalent bond.

ii. They have empty conduction band.

iii. They have almost filled valence band.

iv. These materials have comparatively narrow energy gap.

3. What are compound semiconductors? Give some important compound

semiconductors. (A.U April 2015)

Semiconductors which are formed by combining third and fifth group elements or
second and sixth group elements in the periodic table are called compound
semiconductors.
4. Mention any four advantages of semiconducting materials. (April 2013, April
2014)

i. It behaves as insulator at 0 K and as conductor at high temperatures.

ii. It has some properties of both conductor and insulator.

iii. On doping, n and p-type semiconductors are produced with charge carriers of
electrons and holes respectively.

iv. It has many applications in electronic field such as manufacturing of diodes,

transistors, LED's, IC etc.

5. What are the differences between elemental semiconductors and compound

semiconductors? (A.U June 2012, April 2014, Dec 2015)
6. Write an expression for the concentration of electrons in the conduction band
of an intrinsic semiconductor. (A.U. Jan 2014)

The concentration of electrons in the conduction band of an intrinsic

semiconductor is given by

where me* → effective mass of electron

EF → Fermi energy level

EC → Energy corresponds to the bottom of conduction band

T → Absolute temperature

7. Write an expression for the concentration of holes in the valence band of an

intrinsic semiconductor. (A.U. May 2015)

The concentration of holes in the valence band is given by

mh* → effective mass of hole

T → absolute temperature

EF → Fermi energy

Ev → Energy corresponds to the top of valence band

8. Write an expression for carrier concentration in n-type semiconductor. (A.U.
May 2015)

The carrier concentration in n-type semiconductor is given by

where

9. Write an expression for carrier concentration of holes in the valence band of

p-type semiconductor. (A.U. Jan 2014)

The carrier concentration in p-type is given by

10. Define Hall-effect and Hall voltage. (A.U. May 2015, Dec 2016)

When a conductor carrying a current (I) is placed in a transverse magnetic field

(B), a potential difference is produced inside the conductor in a direction normal to
the directions of the current and magnetic field.

This phenomenon is known as Hall-effect and the generated voltage is called Hall-
voltage.

11. Mention the uses of Hall effect. e uses of Hall effect (A.U. May 2013, June
2014)

i. It is used to find type of semiconductor.

ii. It is used to measure carrier concentration.

iii. It is used to find mobility of charge carrier.

iv. It is used to measure the magnetic flux density using a semiconductor sample of
known Hall coefficient.

12. What are the differences between intrinsic and extrinsic semiconductor?
(A.U 2008, June 2009, 2012)

13. What are the differences between n-type and p-type semiconductor?
UNIT-IV

1. What are optical materials?

The materials which are sensitive to light are known as Optical materials. These
optical materials exhibit a variety of optical properties.

2. What are the type of optical materials?

Generally, optical materials are classified into three types

based on the nature of propagation of light namely,

(i)Transparent

(ii) Translucent

(iii) Opaque

3. Define scattering of light.

It is a process by which the intensity of the wave attenuates as it travels through a

medium.
4. Define carrier generation and recombination.

The carrier generation is the process whereby electrons and holes are created. The
recombination is the process whereby electrons and holes are annihilated.

5. What are types of carrier generations?

(i) Photogeneratione

(ii) Phonon generation

(iii) Impact ionization

6. What are types of recombination process?

(a) Radiative Recombination

(b) Shockley-Read-Hall Recombination

(c) Auger Recombination

7. What is solar cell?

It is a P-N junction diode which converts solar energy (light energy) into electrical
energy.

8. What is LED?

It is a p-n junction diode which emits light when it is forward biased.

9. What is the basic principle behold LED?

The injection of electrons into the p- region from n- region makes a direct
transition from the conduction band to valence band. Then, the electrons
recombine with holes and emits holes and photons of energy

The forbidden gap energy is given by

Eg = hv
10. What are the advantages of LEDs?

i. LEDs are smaller in size. A number of LEDs can be stacked together in a small
space to form numerical display.

ii. LED's can be turned ON and OFF in less than 1 nanosecond (10 -9 second). So,
they are known as fast devices.

iii. Variety of LEDs are available which emit light in bas so different colours like
red, green, yellow etc.

iv. Light modulation can be achieved with pulse supply

v. It has long life time.

vi. It has low drive voltage and low noise.

vii. It is easily interfaced to digital logic circuits.

viii. It can be operated over a wide range of temperatures.

11. What are the disadvantages of LEDs?

i. They require high power.

ii. Their preparation cost is high when compared to LCD.

12. What are the applications uses of LEDs?

i. Because of their miniature size, they are widely used in numeric and
alphanumeric display devices.

ii. They are used as indicator lamps.

iii. They are used in light sources in fiber-optic communication system.

iv. They are used Infrared LEDs are used in burglar alarms.
v. They are used in image sensing circuits used for picture phone.

13. What is an organic light emitting diodes?

Organic light emitting diodes (OLEDs) are solid state devices made up of thin
films of organic molecules that produce light with the application of electricity.

14. What are advantages of OLED?

i. OLED's are tough enough to use in portable devices such ons I as cellular
phones, digital video cameras, DVD players, car audio equipment etc.,

ii. Can be viewed up to 160 degrees.

iii. High information applications including videos and graphics (Active matrix)

iv. OLEDs are paper-thin.

v. Upto 20% to 50% cheaper than LCD processes.

vi. They hold the ability to handle streamlined video, which could revolutionize the
display and cellular phone market.

vii. Takes less power.

15. What are drawbacks of OLED?

i. The biggest technical problem for OLEDs is the limited lifetime of the organic
materials.

ii. The intrusion of water into displays can damage or destroy the organic
materials.

iii. Color - The reliability of the OLED is still not upto the mark. After a month of
use, the screen becomes non-uniform.

16. What are the applications of OLED?

i. OLED technology is used in commercial applications such novels small screens f
as small screens form phones and portable digital audio players (MP3 players), car
radios, digital cameras and high-resolution micro displays for head-mounted
displays.

ii. They can be used in television screens, computer displays, advertising,

information and indication.

iii. OLEDs can also be used in light sources for general space illumination and
large-area light-emitting elements.

17. What is a laser diode?

It is a specially fabricated pn junction diode. This diode emits laser light when it is
forward - biased.

18. What are the advantages of Laser diodes?

This laser is very small in size and compact.

i. It has high efficiency.

ii. The laser output can be easily increased by increasing the junction current.

iii. It is operated with less power than ruby and CO2 lasers.

iv. It requires very little additional equipment.

v. It emits a continuous wave output or pulsed output.

19. What are the applications of Laser diodes?

i. Used in fibre optic communication.

ii. Used in various measuring devices such as range finders, bar-code readers.

iii. Used in printing industry both as light sources for scanning images and for
resolution printing plate manufacturing.
iv. Infrared and red laser diodes are common in CD players, CD-ROM and DVD
technology. Violet lasers are used in HD - DVD and Blue-ray technology.

v. High power laser diodes are used in industrial applications such as heat treating,
cladding, seam welding and for pumping other lasers.

vi. Used in laser medicine especially, dentistry.

20. What is electro optic effect?

Changing the refractive index and other optical characteristics of a medium by the
application of electric field is called electro-optic effect.

UNIT-V

1. Define nano materials.

Nanophase materials are newly developed materials with grain size at the
nanometre range (10-9 m), i.e., in the order of 1 - 100 nm. The particle size in a
nano material is 1 - 100 nm.

2. Define density of states.

It is defined as the number of available electron states per unit volume in an energy
interval E and E + dE. It is denoted by Z (E).

3. Define Fermi energy.

It is defined as the highest energy level occupied by the electron at OK in metal.

4. What is a quantum confinement?

It is a process of reduction of the size of the solid such that the energy levels inside
become discrete.

5. What is quantum structure?

When a bulk material is reduced in its size, atleast one of its dimension, in the
order of few nanometres, then the structure is known as quantum structure.

6. What is quantum size-effect?

When the size of a nanocrystal becomes smaller than the de Broglie wavelength,
electrons and holes get spatially confined, electrical dipoles get generated, the
discrete energy levels are formed.

As the size of the material decreases, the energy separation between adjacent levels
increases. The density of states of nanocrystals is positioned in between discrete
(as that of atoms and molecules) and continuous (as in crystals).

Quantum size effect is most significant for semiconductor nanoparticles.

7. What is single electron phenomena?

Present day, transistors require 10,000 electrons. Rather than moving many
electrons through transistors, it may very well be practical and necessary to move
electrons one at a time. The phenomena in known as single electron phenomena.

8. Define Coulomb - Blockade effect.

The charging effect which blocks the injection or rejection. of a single charge into
or from a quantum dot is called Coulomb blockade effect.

9. What is single electron tunneling?

The quantization of charge can dominate and tunneling of single electrons across
leaky capacitors carries the current. This is called single electron tunneling.

10. What is a Single Electron Transistor?

SET is three-terminal switching devices which can transfer electrons from source
to drain one by one.

11. What are the advantages of single electron transistor?

i. The fast information transfer velocity between cells (almost near optic velocity)
is carried out via electrostatic interactions only.

ii. No wire is needed between arrays. The size of each cell guille can be as small as
2.5 nm. This made them very suitable for high density memory.

iii. This can be used for the next generation quantum computer.

12. What are the limitations of single electron transistor?

i. In order to operate SET circuit at room temperature, the size of the quantum dot
should be smaller than 10 nm.

ii. It is very hard to fabricate by traditional optical lithography and semiconductor

process.

iii. The methods must be developed for connecting the individual structures into
logic circuits and these circuits must be arranged into larger 2D patterns.

13. What are the applications of single electron Transistor?

i. A variety of digital logic functions, including AND or NOR gates, is obtained

based on SET operating at room temperature.

ii. It is used for mass data storage.

iii. It is used in highly sensitive electrometer.

iv. SET can be used as a temperature probe, particularly aidTo in the range of very
low temperatures.

v. SET is a suitable measurement set-up for single electron spectroscopy.

vi. It is used for the fabrication of a homo-dyn receiver operating at frequencies

between 10 and 300 MHz.

14. What is a carbon nano tube?

The carbon nanotubes are the wires of pure carbon like rolled sheets of graphite or
like soda straws.

15. What are the types of carbon nano tube structure?

Three types of nanotube structures are considered by rolling a graphite sheet with
different orientations about the axis.

They are

(i) Armchair structure

(ii) Zig-zag structure

(iii) Chiral structure luc

16. How carbon nanotubes are classified

Based on the number of layers, the carbon nanotubes are classified as

(i) Single-walled (SWNTs)

(ii) Multi-walled (MWNTs).

In multi-walled nanotubes, more than one CNTs are coaxially arranged.