www.sprengg4u.blogspot.in UNIT-I CONDUCTING MATERIALS 1. Define Mobility of electrons. It is defined as the velocity acquired by the electron per unit electric field µ=v/E 2. Define Wiedemann- Franz law. Give the value of Lorentz number. The ratio between the thermal conductivity and the electrical conductivity of a metal is directly proportional to the absolute temp of the metal. 3. Define Fermi energy level and Fermi energy with its importance. It is the highest reference energy level of a particle at absolute zero. It is the state at which the probability of electron occupation is 50% at any temp. 4. Define electrical conductivity. It is defined as the quality of electricity flowing per unit area per unit time maintained at unit potential gradient. 5. What are the drawbacks of classical free electron theory?  It is a macroscopic theory.  This theory cannot explain the Compton, photo – electric effect, paramagnetic, ferromagnetism, etc. The Lorentz number by classical theory does not have good agreement with the experimental value and is rectified by quantum theory.

6. Write the Fermi- Dirac distribution function. Fermi-dirac distribution function represents the probability of an electron occupying a given energy level. 7. Define density of states and given an example and state its importance. Density of states Z(E)dE is defined as the number of available energy states per unit volume in an energy interval dE. 8. Define mean free path. The average distance travelled between two successive collisions is called mean free path. It is denoted by the letter. ( λ ) 9. Define Drift velocity and give its formula. It defined as the average velocity acquired by the free electron in a particular direction, due to the application of electric field and is denoted by the letter vd

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www.sprengg4u.blogspot.in UNIT-II SEMI CONDUCTING MATERIALS 1. State the properties of a semiconductor.  They have negative temp coefficient of resistance.  The resistivity lies between 10-4 to 0.5 ohm-meter.  At OK they behave as insulators. 2. What are the applications of Hall Effect?  The mobility of charge carriers µe and µh  The sign of the current carrying charges.  It is used to find the power flow in an electromagnetic wave. 3. What is meant by Hall Effect? When a current carrying conductor is placed in a transverse magnectic field, an electric field is produced inside the conductor in a direction normal to both the current and the magnetic field. 4. Compare elemental semiconductors and compound semiconductor? S.No

Elemental semiconductor

1.

They are made of single element Ge,Si They are indirect band gap semiconductors. Heat is produced due to recombination.

2. 3.

Compound semiconductor Made of compounds GaP,MgO They are called as direct bandgap semiconductors. Photons are emitted during recombination.

5. What is meant by intrinsic semiconductor and extrinsic semiconductor? S.No

Intrinsic semiconductor

Extrinsic semiconductor

1.

Semi conductor in a pure form

2.

They have low electrical conductivity They have low operating temp.

Semiconductor which are doped with impurity They have high electrical conductivity They have high operating temp.

3.

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www.sprengg4u.blogspot.in 6. Compare n-type and p-type semiconductor. S.No

n- type

p- type

1. 2.

Pentavalent impurity Here electrons are majority and holes are minority Donar energy levels very to conduction band

Trivalent impurity. Here holes are majority and electrons are minority acceptor energy levels very to valence band

3.

UNIT-III MAGNETIC AND SUPERCONDUCTING MATERIALS 1. Compare type I and Type II super conductor. S.No 1.

2. 3.

Type I

Type II

Type I super conductor becomes a normal conductor abruptly at critical magnetic field Here we have only one critical field No mixed state

Type II super conductor loses its super conductor properly gradually due to increase in magnetic field Here we have two critical field Vortex state is present.

2. Explain Meissner effect. When a super conducting material is kept in an external magnetic field under the condition when T≤ Tc and H≤ Hc the magnetic flux lines are completely excluded from the material and this phenomenon is called meissner effect. 3. What are high temp super conductors? High temp superconductors are the one which has the transition temp above 77K , because cooling can be made by liquid nitrogen instead of liquid helium which is costly than nitrogen. 4. Give any two applications of super conductors  It is used in magnetic levitation  It is used in computers transmission lines  It is used in NMR  It is used in magneto hydrodynamic power generation to maintain plasma in the body.

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www.sprengg4u.blogspot.in 5. What are the properties of a superconductor?  They have zero resistivity.  Perfect diamagnetism  The super conducting property can be destroyed due to the application of magnetic and electric fields. 6. What is meant by persistent current? When d.c current of large magnitude is once induced in a super conducting ring , then due to the diamagnetic property of the super conductor, the magnetic flux is trapped inside the ring . 7. Define cooper pairs? The pair of electrons formed due to the electron-lattice-electron interaction, with equal and opposite momentum and spins having the wave vectors K-q and k+q are called Cooper pairs. 8. Write a short note on SQUIDS. Super conducting quantum interference devices. A small change in magnetic field produces large variation in the quantum flux. 9. What are soft and hard magnetic materials? S.No

Soft

Hard

1.

They can be easily magnetised and demagnetized. Movement of domain wall is easy Hysteresis loop is very steep

They cannot be easily magnetised

2. 3.

Movement of domain wall is not easy Hysteresis loop is very broad.

10. What are ferrites? They are made by two or more different kinds of atoms. Its general formula is given by X2+ Fe23+ O4. 11. Define energy product The product of retentively and the coercivity is Known as energy product. It represents the maximum amount energy stored in the specimen. 12. State the applications of ferrites.  They are used in two port devices such as circulator  They are used in computers and data processing circuits.  They are used in switching circuits and parametric amplifiers.

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www.sprengg4u.blogspot.in 13. Define Bohr magneton. The orbital magnetic moment and the spin magnetic moment of an electron in an atom can be expressed in terms of atomic unit of magnetic moment 14. What are the four type’s magnetic domains?  Exchange energy  Anisotropy energy  Domain wall energy  Magneto- strictive energy

UNIT-IV DIELECTRIC MATERIALS 1. Define electronic polarization. When a dielectric material is kept in external field , the positive and negative charges in the dielectrics moves in opposite direction, thereby creating a dipole moment. 2. Define Local field (or) internal field. Long range of coulombs forces which are created due to the dipoles are called internal field or local field. 3. What is meant by dielectric loss? The dielectric and certain amount of electrical energy is dissipated in the form of heat energy, this loss in energy in the form of heat is called dielectric loss. 4. What is meant by dielectric break down? When external field applied to a dielectric material is greater than the critical field, the dielectric losses its insulating property and becomes conducting. Therefore a large current flows through the material. 5. List out the applications of ferro- electrics.  It is used to produce ultrasonics.  It is used in SONAR  It is used to bond the bones in the human body.  It is used production of piezo- electric materials.  6. Define ionic polarization. The process of displacement of cations and anions in the opposite directions, of a dielectric material kept in external in external electric field.

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www.sprengg4u.blogspot.in 7. What is meant by ferro electricity? When a dielectric material exhibits electric polarization even in the absence of external field, it is known as ferro electricity and these materials are termed as ferroelectrics. 8. What are differences between polar and non-polar molecules? S.No 1. 2. 3.

POLAR

NON POLAR

Molecules have permanent dipole moments Molecules are highly temp dependent. HCl

Molecules do not have permanent dipole moments Molecules are independent of temperature. CCl4

UNIT-V MODERN ENGINEERING MATERIALS 1. What are metallic glasses? Met glasses are the amorphous metallic solids which have high strength, good magnetic properties and better corrosion resistance and wil possess both the properties of metals and glasses. 2. What are shape memory alloys? When material is heated above the transformation temp, then there will be some change in the crystal structure. Such materials are called shape memory alloys. 3. What are nano materials? Give examples. Nano materials are the materials in which the atoms size is in the order of 1 to 100 nano and these atoms will not move away from each other. Ex: ZnO,Ni,Pt etc. 4. Mention properties of metglasses?  Metglasses have TCP structure rather than hexagonal closely packed structure.  Very strong in nature.  They possess malleability, ductility etc.  5. What are the properties of SMA?  They have pseudo- elastic and super elastic property  They exhibit hysteresis curve, during cooling and beating process.

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www.sprengg4u.blogspot.in 6. Give any three applications of SMA  It is used in Eye glass frames. Toys, helicopter blades.  They are also used in fire safety valves, coffer maker.  They are used in relays and activators. 7. What are the properties of nano particles?  The energy bands in these materials will be very narrow.  In nano materials a large number of atoms will be present at the surface.  Interparticles spacing is very less in nano- materials. 8. List out any recent applications of nano- meterials.  It is used in ICs,optical switches, mass sensors etc.  Recently nano-robots were designed, which are used to remove the damaged cancer cells  It is used in the production of DNA-chips, bio-sensors etc.

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